The Xpand generator framework provides textual languages, that are useful in different contexts in the MDSD process (e.g. checks, extensions, code generation, model transformation). Each language (Check, Xtend, and Xpand) is built up on a common expression language and type system. Therefore, they can operate on the same models, metamodels and meta-metamodels and you do not need to learn the syntax again and again, because it is always the same.
The expressions framework provides a uniform abstraction layer over different meta-meta-models (e.g. EMF Ecore, Eclipse UML, JavaBeans, XML Schema etc.). Additionally, it offers a powerful, statically typed expressions language, which is used in the various textual languages.
The abstraction layer on API basis is called a type system. It provides access to built-in types and different registered metamodel implementations. These registered metamodel implementations offer access to the types they provide. The first part of this documentation describes the type system. The expression sub-language is described afterwards in the second part of this documentation. This differentiation is necessary because the type system and the expression language are two different things. The type system is a kind of reflection layer, that can be extended with metamodel implementations. The expression language defines a concrete syntax for executable expressions, using the type system.
The Java API described here is located in the org.eclipse.xpand.type package and is a part of the subproject core.expressions.
Every object (e.g. model elements, values, etc.) has a type. A type contains properties and operations. In addition it might inherit from other types (multiple inheritance).
Types have a simple name (e.g. String
)
and an optional namespace used to distingish between two types with
the same name (e.g. my::metamodel
). The
delimiter for name space fragments is a double colon
"::
". A fully qualified name looks like this:
my::fully::qualified::MetaType
The namespace and name used by a specific type is defined by the
corresponding MetaModel
implementation. The EmfMetaModel
, for instance, maps
EPackages
to namespace and
EClassifiers
to names. Therefore, the name of the Ecore element
EClassifier
is called:
ecore::EClassifier
If you do not want to use namespaces (for whatever reason), you can always implement your own metamodel and map the names accordingly.
The built-in type system also contains the following collection
types: Collection
,
List
and Set
. Because
the expressions language is statically type checked and we do not like
casts and ClassCastExceptions
, we introduced
the concept of parameterized types. The type
system does not support full featured generics, because we do not need
them.
The syntax is:
Collection[my::Type] List[my::Type] Set[my::Type]
Each type offers features. The type (resp. the metamodel) is responsible for mapping the features. There are three different kinds of features:
Properties
Operations
Static properties
Properties are straight forward: They have a name and a type. They can be invoked on instances of the corresponding type. The same is true for Operations. But in contrast to properties, they can have parameters. Static properties are the equivalent to enums or constants. They must be invoked statically and they do not have parameters.
As mentioned before, the expressions framework has several built-in types that define operations and properties. In the following, we will give a rough overview of the types and their features. We will not document all of the operations here, because the built-in types will evolve over time and we want to derive the documentation from the implementation (model-driven, of course). For a complete reference, consult the generated API documentation (http://www.openarchitectureware.org/api/built-ins/).
The Void
type can be specified as the
return type for operations, although it is not recommended, because
whenever possible expressions should be free of side effects whenever
possible.
The type system doesn't have a concept data type. Data types are
just types. As in OCL, we support the following types:
String
, Boolean
,
Integer
, Real
.
String
: A rich and convenient
String
library is especially important
for code generation. The type system supports the '+' operator
for concatenation, the usual
java.lang.String
operations
(length()
, etc.) and some special
operations (like toFirstUpper()
,
toFirstLower()
, regular expressions,
etc. often needed in code generation templates).
Boolean
: Boolean
offers the usual operators (Java syntax): &&, ||, !,
etc.
Integer
and
Real
: Integer
and Real
offer the usual compare
operators (<,>,<=,>=) and simple arithmetics
(+,-,*,/). Note that Integer
extends Real
!
The type system has three different Collection types.
Collection
is the base type, it provides several operations known
from java.util.Collection
. The other two types
(List
, Set
) correspond to their
java.util equivalents, too.
The type system describes itself, hence, there are types for the
different concepts. These types are needed for reflective programming.
To avoid confusion with metatypes with the same name (it is not
unusual to have a metatype called Operation
,
for instance) we have prefixed all of the types with the namespace
xpand
. We have:
xpand2::Type
xpand2::Feature
xpand2::Property
xpand2::StaticProperty
xpand2::Operation
By default, the type system only knows the built-in types. In
order to register your own metatypes (e.g. Entity
or State
), you need to register a respective
metamodel implementation with the type system. Within a metamodel
implementation the Xpand type system elements (Type, Property, Operation) are mapped to an arbitrary other type system (Java
reflections, Ecore or XML Schema).
For instance, if you want to have the following JavaBean act as a metatype (i.e. your model contains instances of the type):
public class Attribute { private String name; private String type; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getType() { return type; } public void setType(String type) { this.type = type; } }
You need to use the JavaMetaModel
implementation which uses the ordinary Java reflection
layer in order to map access to the model.
So, if you have the following expression in e.g. Xpand:
myattr.name.toFirstUpper()
and myattr
is the name of a local variable
pointing to an instance of Attribute
. The Xpand
type system asks the metamodel implementations, if they 'know' a type
for the instance of Attribute. If you have the
JavaMetaModel
registered it will return an
xpand2::Type
which maps to the underlying Java
class. When the type is asked if it knows a property
'name
', it will inspect the Java class using the
Java reflection API.
The JavaMetaModel implementation shipped with Xpand can be configured with a strategy [GOF95-Pattern] in order to control or change the mapping. For instance, the JavaBeansStrategy maps getter and setter methods to simple properties, so we would use this strategy for the example above.
You should know that for each Metamodel
implementation you use at runtime, you need to have a so
called MetamodelContributor
extension for the
plugins to work with. If you just use one of the standard metamodel
implementations (EMF, UML2 or Java) you don't have to worry about it,
since Xpand is shipped with respective MetamodelContributors (see the
corresponding docs for details). If you need to implement your own
MetamodelContributor
you should have a look at the Eclipse plug-in reference
doc.
You need to configure your Xpand language components with the respective metamodel implementations.
A possible configuration of the Xpand2
generator component looks like this:
<component class="org.eclipse.xpand2.Generator"> <metaModel class="org.eclipse.type.emf.EmfMetaModel"> <metaModelPackage value="my.generated.MetaModel1Package"/> </metaModel> <metaModel class="org.eclipse.type.emf.EmfMetaModel"> <metaModelFile value="my/java/package/metamodel2.ecore"/> </metaModel> ... </component>
In this example the EmfMetaModel
implementation is configured two times. This means that we want to use
two metamodels at the same time, both based on EMF. The
metaModelPackage property is a property that is
specific to the EmfMetaModel
(located in the
core.emftools
project). It points to the
generated EPackages
interface. The second meta
model is configured using the Ecore file. You do no need to have a
generated Ecore model for Xpand in order to work. The
EmfMetaModel
works with dynamic EMF models just
as it works with generated EMF models.
With Xpad you can work on different kinds of Model representations at the same time in a transparent manner. One can work with EMF models, XML DOM models, and simple JavaBeans in the same Xpand template. You just need to configure the respective MetaModel implementations.
If you want to do so you need to know how the type lookup works. Let us assume that we have an EMF metamodel and a model based on some Java classes. Then the following would be a possible configuration:
<component class="org.eclipse.xpand2.Generator"> <metaModel class="org.eclipse.internal.xtend.type.impl.java.JavaMetaModel"/> <metaModel class="org.eclipse.xtend.typesystem.emf.EmfMetaModel"> <metaModelFile value="my/java/package/metamodel.ecore"/> </metaModel> ... </component>
When the runtime needs to access a property of a given object,
it asks the metamodels in the configured order. Let us assume that our
model element is an instance of the Java type
org.eclipse.emf.ecore.EObject
and it is a dynamic
instance of an EMF EClass MyType
.
We have three Metamodels:
The first one will return the type Object
(not java.lang.Object
but
Object
of Xpand). At this point the type
Object
best fits the request, so it will act as
the desired type.
The second metamodel returns a type called
org::eclipse::emf::ecore::EObject
The type system
will check if the returned type is a specialization of the current
'best-fit' type (Object
). It is, because it
extends Object
(Every metatype has to extend
Object
). At this time the type system assumes
org::eclipse::emf::ecore::EObject
to be the
desired type.
The third metamodel will return
metamodel::MyType
which is the desired type. But
unfortunately it doesn't extend
org::eclipse::emf::ecore::EObject
as it has
nothing to do with those Java types. Instead it extends
emf::EObject
which extends
Object
.
We need to swap the configuration of the two metamodels to get the desired type.
<component class="org.eclipse.xpand2.Generator"> <metaModel class="org.eclipse.xtend.typesystem.emf.EmfMetaModel"> <metaModelFile value="my/java/package/metamodel.ecore"/> </metaModel> <metaModel class="org.eclipse.internal.xtend.type.impl.java.JavaMetaModel"/> ... </component>
The expression sub-language is a syntactical mixture of Java and OCL. This documentation provides a detailed description of each available expression. Let us start with some simple examples.
Accessing a property:
myModelElement.name
Accessing an operation:
myModelElement.doStuff()
simple arithmetic:
1 + 1 * 2
boolean expressions (just an example:-)):
!('text'.startsWith('t') && ! false)
There are several literals for built-in types:
There are naturally no literals for object, but we have two operators:
equals:
obj1 == obj2
not equals:
obj1 != obj2
The literal for types is just the name of the type (no '.class' suffix, etc.). Example:
String // the type string my::special::Type // evaluates to the type 'my::special::Type'
The literal for static properties (aka enum literals) is correlative to type literals:
my::Color::RED
There are two different literal syntaxes (with the same semantics):
'a String literal' "a String literal" // both are okay
For Strings the expression sub-language supports the plus operator that is overloaded with concatenation:
'my element '+ ele.name +' is really cool!'
Note, that multi-line Strings are supported.
The boolean literals are:
true false
Operators are:
true && false // AND true || false // OR ! true // NOT
The syntax for integer literals is as expected:
// integer literals 3 57278 // real literals 3.0 0.75
Additionally, we have the common arithmetic operators:
3 + 4 // addition 4 - 5 // subtraction 2 * 6 // multiplication 3 / 64 // divide // Unary minus operator - 42 - 47.11
Furthermore, the well known compare operators are defined:
4 > 5 // greater than 4 < 5 // smaller than 4 >= 23 // greater equals than 4 <= 12 // smaller equals than
Like OCL, the Xpand expression sub-language defines several special operations on collections. However, those operations are not members of the type system, therefore you cannot use them in a reflective manner.
Sometimes, an expression yields a large collection, but one is
only interested in a special subset of the collection. The expression
sub-language has special constructs to specify a selection out of a
specific collection. These are the select
and
reject
operations. The select specifies a
subset of a collection. A select
is an
operation on a collection and is specified as follows:
collection.select(v | boolean-expression-with-v)
select
returns a sublist of the
specified collection. The list contains all elements for which the
evaluation of boolean-expression-with-v results is
true
. Example:
{1,2,3,4}.select(i | i >= 3) // returns {3,4}
A special version of a select expression is
typeSelect
. Rather than providing a boolean
expression a class name is here provided.
collection.typeSelect(classname)
typeSelect
returns that sublist of the
specified collection, that contains only objects which are an instance
of the specified class (also inherited).
The reject
operation is similar to the
select
operation, but with
reject
we get the subset of all the elements
of the collection for which the expression evaluates to
false
. The reject
syntax
is identical to the select
syntax:
collection.reject(v | boolean-expression-with-v)
Example:
{1,2,3,4}.reject(i | i >= 3) // returns {1,2}
As shown in the previous section, the
select
and reject
operations always result in a sub-collection of the original
collection. Sometimes one wants to specify a collection which is
derived from another collection, but which contains objects that are
not in the original collection (it is not a sub-collection). In such
cases, we can use a collect
operation. The
collect
operation uses the same syntax as the
select
and reject
and is written like this:
collection.collect(v | expression-with-v)
collect
again iterates over the target
collection and evaluates the given expression on each element. In
contrast to select
, the evaluation result is
collected in a list. When an iteration is finished the list with all
results is returned. Example:
namedElements.collect(ne | ne.name) // returns a list of strings
As navigation through many objects is very common, there is a shorthand notation for collect that makes the expressions more readable. Instead of
self.employee.collect(e | e.birthdate)
one can also write:
self.employee.birthdate
In general, when a property is applied to a collection of
Objects, it will automatically be interpreted as a
collect
over the members of the collection
with the specified property.
The syntax is a shorthand for collect
,
if the feature does not return a collection itself. But sometimes we
have the following:
self.buildings.rooms.windows // returns a list of windows
This syntax works, but one cannot express it using the
collect
operation in an easy way.
Often a boolean expression has to be evaluated for all elements
in a collection. The forAll
operation allows specifying a Boolean expression, which
must be true
for all objects in a collection in
order for the forAll
operation to return
true
:
collection.forAll(v | boolean-expression-with-v)
The result of forAll
is
true
if
boolean-expression-with-v
is true
for all the elements contained in a collection. If
boolean-expression-with-v
is
false
for one or more of the elements in the
collection, then the forAll
expression
evaluates to false
.
Example:
{3,4,500}.forAll(i | i < 10) // evaluates to false (500 < 10 is false)
Often you will need to know whether there is at least one
element in a collection for which a boolean is
true
. The exists operation allows you to specify a
Boolean expression which must be true
for at least
one object in a collection:
collection.exists(v | boolean-expression-with-v)
The result of the exists operation is true
if
boolean-expression-with-v
is
true
for at least one element of collection. If the
boolean-expression-with-v
is
false
for all elements in collection, then the
complete expression evaluates to false
.
Example:
{3,4,500}.exists(i | i < 10) // evaluates to true (e.g. 3 < 10 is true)
sortBy
[1]If you want to sort a list of elements, you can use the higher
order function sortBy
. The list you invoke the
sortBy
operation on, is sorted by the results
of the given expression.
Example:
myListOfEntity.sortBy(entity | entity.name)
In the example the list of entities is sorted by the name of the
entities. Note that there is no such Comparable
type in Xpand. If the values returned from the expression are instances
of java.util.Comparable
the
compareTo
method is used, otherwise
toString()
is invoked and the the result is
used.
More Examples â all the following expressions return
true
:
{'C','B','A'}.sortBy(e | e) == {'A','B','C'} {'AAA','BB','C'}.sortBy(e | e.length) == {'C','BB','AAA'} {5,3,1,2}.sortBy(e | e) == {1,2,3,5} {5,3,1,2}.sortBy(e | e - 2 * e) == {5,3,2,1} ...
There are two different forms of conditional expressions. The first one is the so-called if expression. Syntax:
condition ? thenExpression : elseExpression
Example:
name != null ? name : 'unknown'
The other one is called switch expression. Syntax:
switch (expression) { (case expression : thenExpression)* default : catchAllExpression }
The default part is mandatory, because
switch
is an expression, therefore it needs to
evaluate to something in any case. Example:
switch (person.name) { case 'Hansen' : 'Du kanns platt schnacken' default : 'Du kanns mi nech verstohn!' }
There is an abbreviation for Boolean expressions:
switch { case booleanExpression : thenExpression default : catchAllExpression }
Expressions and functional languages should be free of side
effects as far as possible. But sometimes there you need invocations
that do have side effects. In some cases expressions even don not have a
return type (i.e. the return type is Void
). If
you need to call such operations, you can use the chain expression.
Syntax:
anExpr -> anotherExpr -> lastExpr
Each expression is evaluated in sequence, but only the result of the last expression is returned. Example:
pers.setName('test') -> pers
This chain expression will set the name
of the
person first, before it returns the person object itself.
The let
expression lets you define local
variables. Syntax is as follows:
let v = expression : expression-with-v
This is especially useful together with a chain- and a create expressions. Example:
let p = new Person : p.name('John Doe') -> p.age(42) -> p.city('New York') -> p
Sometimes you don't want to pass everything down the call stack by
parameter. Therefore, we have the GLOBALVAR
expression. There are two things you need to do, to use
global variables.
Each workflow component using the expression framework (Xpand, Check and Xtend) can be configured with global variables. Here is an example:
<workflow> .... stuff <component class="org.eclipse.xpand2.Generator"> ... usual stuff (see ref doc) <globalVarDef name="MyPSM" value="slotNameOfPSM"/> <globalVarDef name="ImplClassSuffix" value="'Impl'"/> </component> </workflow>
If you have injected global variables into the respective component, you can call them using the following syntax:
GLOBALVAR ImplClassSuffix
Note, we don't have any static type information. Therefore
Object
is assumed. So, you have to down cast
the global variable to the intended type:
((String) GLOBALVAR ImplClassSuffix)
It is good practice to type it once, using an Extension and then always refer to that extension:
String implClassSuffix() : GLOBALVAR ImplClassSuffix; // usage of the typed global var extension ImplName(Class c) : name+implClassSuffix();
The expressions language supports multiple dispatching . This means that when there is a bunch of overloaded
operations, the decision which operation has to be resolved is based on
the dynamic type of all parameters (the implicit
'this
' included).
In Java only the dynamic type of the 'this
'
element is considered, for parameters the static type is used. (this is
called single dispatch)
Here is a Java example:
class MyClass { boolean equals(Object o) { if (o instanceof MyClass) { return equals((MyClass)o); } return super.equals(o); } boolean equals(MyType mt) { //implementation... } }
The method equals(Object o)
would not
have to be overwritten, if Java would support multiple dispatch.
The expression language is statically type checked. Although there are many concepts that help the programmer to have really good static type information, sometimes. one knows more about the real type than the system. To explicitly give the system such an information casts are available. Casts are 100% static, so you do not need them, if you never statically typecheck your expressions!
The syntax for casts is very Java-like:
((String)unTypedList.get(0)).toUpperCase()
Xpand also provides a language to specify constraints
that the model has to fulfill in order to be correct. This
language is very easy to understand and use. Basically, it is built around
the expression syntax that has been discussed in detail in the previous
section. Constraints specified in the Check
language have to be stored in files with the file extension
.chk
. Furthermore, these files have to be on the Java classpath,
of course, in order to be found. Let us look at an example, in order to
understand, what these constraints look like and what they
do:
import data; context Attribute ERROR "Names have to be more than one character long." : name.length > 1;
Now, let us look at the example line by line:
First, the metamodel has to be imported.
Then, the context is specified for which the constraint
applies. In other words, after the context
keyword, we
put the name of the metaclass that is going to be checked by the
constraint. Then, there follows either ERROR
or
WARNING
, These keywords specify what kind of action
will be taken in case the constraint fails:
Table 1.1. Types of action for Check constraints
WARNING | If the constraint fails, the specified message is printed, but the workflow execution is not stopped. |
ERROR | If the constraint fails, the specified message is printed and all further processing is stopped. |
Now, the message that is put in case that the constraint fails is specified as a string. It is possible to include the value of attributes or the return value of functions into the message in order to make the message more clear. For example, it would be possible to improve the above example by rewriting it like this:
import data; context Attribute ERROR "Name of '" + name + "too short. Names have to be more than one character long." : name.length > 1;
Finally, there is the condition itself, which is specified by
an expression, which has been discussed in detail in the previous
section. If this expression is true
, the
constraint is fulfilled.
![]() | |
Please always keep in mind that the message that is associated
with the constraint is printed, if the condition of the constraint is
|
The Check language of Xpand also provides so called . These conditions allow to apply a check constraint only to model elements that meet certain criteria. Specifying such a guard condition is done by adding an if clause to the check constraint. The if clause has to be added after the context clause as demonstrated by the following example:
import data; context Attribute if name.length > 1 ERROR "Attribute names have to start with an 'a'" : name.startsWith("a");
Like the expressions sublanguage that summarizes the syntax of expressions for all the other textual languages delivered with the Xpand framework, there is another commonly used language called Xtend.
This language provides the possibility to define rich libraries of independent operations and non-invasive metamodel extensions based on either Java methods orXtend expressions. Those libraries can be referenced from all other textual languages, that are based on the expressions framework.
An extend file must reside in the Java class path of the
used execution context. Additionally it is file extension must be
*.ext
. Let us have a look at an extend file.
import my::metamodel;extension other::ExtensionFile; /** * Documentation */ anExpressionExtension(String stringParam) : doingStuff(with(stringParam)) ; /** * java extensions are just mappings */ String aJavaExtension(String param) : JAVA my.JavaClass.staticMethod(java.lang.String) ;
The example shows the following statements:
import statements
extension import statements
expression or java extensions
We have single- and multi-line comments. The syntax for single line comments is:
// my comment
Multi line comments are written like this:
/* My multi line comment */
Using the import statement one can import name spaces of different types.(see expressions framework reference documentation).
Syntax is:
import my::imported::namespace;
Extend does not support static imports or any similar concept. Therefore, the following is incorrect syntax:
import my::imported::namespace::*; // WRONG! import my::Type; // WRONG!
You can import another extend file using the extension statement. The syntax is:
extension fully::qualified::ExtensionFileName;
Note, that no file extension (*.ext
) is
specified.
The syntax of a simple expression extension is as follows:
ReturnType extensionName(ParamType1 paramName1, ParamType2...): expression-using-params;
Example:
String getterName(NamedElement ele) : 'get'+ele.name.firstUpper();
There are two different ways of how to invoke an extension. It can be invoked like a function:
getterName(myNamedElement)
The other way to invoke an extension is through the "member syntax":
myNamedElement.getterName()
For any invocation in member syntax, the target expression (the member) is mapped to the first parameter. Therefore, both syntactical forms do the same thing.
It is important to understand that extensions are not members of the type system, hence, they are not accessible through reflection and you cannot specialize or overwrite operations using them.
The expression evaluation engine first looks for an appropriate operation before looking for an extension, in other words operations have higher precedence.
For most extensions, you do not need to specify the return type, because it can be derived from the specified expression. The special thing is, that the static return type of such an extension depends on the context of use.
For instance, if you have the following extension
asList(Object o): {o};
the invocation of
asList('text')
has the static type List[String]. This means you can call
asList('text').get(0).toUpperCase()
The expression is statically type safe, because its return type is derived automatically.
There is always a return value, whether you specify it or not,
even if you specify explicitly 'Void
'.
See the following example.
modelTarget.ownedElements.addAllNotNull(modelSource.contents.duplicate())
In this example duplicate() dispatches polymorphically. Two of the extensions might look like:
Void duplicate(Realization realization): realization.Specifier().duplicate()-> realization.Realizer().duplicate() ; create target::Class duplicate(source::Class): ... ;
If a 'Realization
' is contained in the
'contents
' list of
'modelSource
', the
'Realizer
' of the
'Realization
' will be added to the
'ownedElements
' list of the
'modelTarget
'. If you do not want to add in the
case that the contained element is a 'Realization' you might change
the extension to:
Void duplicate(Realization realization): realization.Specifier().duplicate()-> realization.Realizer().duplicate() -> {} ;
There is only one exception: For recursive extensions the return type cannot be inferred, therefore you need to specify it explicitly:
String fullyQualifiedName(NamedElement n) : n.parent == null ? n.name : fullyQualifiedName(n.parent)+'::'+n.name ;
Recursive extensions are non-deterministic in a static context, therefore, it is necessary to specify a return type.
If you call an extension without side effects very often, you
would like to cache the result for each set of parameters, in order
improve the performance. You can just add the keyword
'cached
' to the extension in order to achieve this:
cached String getterName(NamedElement ele) : 'get'+ele.name.firstUpper() ;
The getterName
will be computed only
once for each NamedElement
.
In some rare cases one does want to call a Java method from inside an expression. This can be done by providing a Java extension:
Void myJavaExtension(String param) : JAVA my.Type.staticMethod(java.lang.String) ;
The signature is the same as for any other extension. The implementation is redirected to a public static method in a Java class.
Its syntax is:
JAVA fully.qualified.Type.staticMethod(my.ParamType1, my.ParamType2, ...) ;
Note that you cannot use any imported namespaces. You have to specify the type, its method and the parameter types in a fully qualified way.
Example:
If you have defined the following Java extension:
Void dump(String s) : JAVA my.Helper.dump(java.lang.String) ;
and you have the following Java class:
package my; public class Helper { public final static void dump(String aString) { System.out.println(aString); } }
the expressions
dump('Hello world!') 'Hello World'.dump()
both result are invoking the Java method void dump(String aString)
Since Version 4.1 the Xtend language supports additional support for model transformation. The new concept is called create extension and it is explained a bit more comprehensive as usual.
Elements contained in a model are usually referenced multiple times. Consider the following model structure:
P / \ C1 C2 \ / R
A package P contains two classes C1 and C2. C1 contains a reference R of type C2 (P also references C2).
We could write the following extensions in order to transform an Ecore (EMF) model to our metamodel (Package, Class, Reference).
toPackage(EPackage x) : let p = new Package : p.ownedMember.addAll(x.eClassifiers.toClass()) -> p; toClass(EClass x) : let c = new Class : c.attributes.addAll(x.eReferences.toReference()) -> c; toReference(EReference x) : let r = new Reference : r.setType(x.eType.toClass()) -> r;
For an Ecore model with the above structure, the result would be:
P / \ C1 C2 | R - C2
What happened? The C2 class has been created 2 times (one time for the package containment and another time for the reference R that also refers to C2). We can solve the problem by adding the 'cached' keyword to the second extension:
cached toClass(EClass x) : let c = new Class : c.attributes.addAll(c.eAttributes.toAttribute()) -> c;
The process goes like this:
start create P
start create C1 (contained in P)
start create R (contained in C1)
start create C2 (referenced from R)
end (result C2 is cached)
end R
end C1
start get cached C2 (contained in P)
end P
So this works very well. We will get the intended structure. But what about circular dependencies? For instance, C2 could contain a Reference R2 of type C1 (bidirectional references):
The transformation would occur like this:
start create P
start create C1 (contained in P)
start create R (contained in C1)
start create C2 (referenced from R)
start create R2 (contained in C2)
start create C1 (referenced from R1)... OOPS!
C1 is already in creation and will not complete until the stack is reduced. Deadlock! The problem is that the cache caches the return value, but C1 was not returned so far, because it is still in construction. The solution: create extensions
The syntax is as follows:
create Package toPackage(EPackage x) : this.classifiers.addAll(x.eClassifiers.toClass()); create Class toClass(EClass x) : this.attributes.addAll(x.eReferences.toReference()); create Reference toReference(EReference x) : this.setType(x.eType.toClass());
This is not only a shorter syntax, but it also has the needed semantics: The created model element will be added to the cache before evaluating the body. The return value is always the reference to the created and maybe not completely initialized element.
The previous section showed how to implement Extensions in Java. This section shows how to call Extensions from Java.
// setup XtendFacade f = XtendFacade.create("my::path::MyExtensionFile"); // use f.call("sayHello",new Object[]{"World"});
The called extension file looks like this:
sayHello(String s) : "Hello " + s;
This example uses only features of the BuiltinMetaModel, in this
case the "+
" feature from the
StringTypeImpl.
Here is another example, that uses the
JavaBeansMetaModel
strategy. This strategy provides as additional feature:
the access to properties using the getter and setter methods.
For more information about type systems, see the Expressions reference documentation.
We have one JavaBean-like metamodel class:
package mypackage; public class MyBeanMetaClass { private String myProp; public String getMyProp() { return myProp; } public void setMyProp(String s) { myProp = s;} }
in addition to the built-in metamodel type system, we register the
JavaMetaModel
with the
JavaBeansStrategy
for our facade. Now, we can use also this strategy in our
extension:
// setup facade XtendFacade f = XtendFacade.create("myext::JavaBeanExtension"); // setup additional type system JavaMetaModel jmm = new JavaMetaModel("JavaMM", new JavaBeansStrategy()); f.registerMetaModel(jmm); // use the facade MyBeanMetaClass jb = MyBeanMetaClass(); jb.setMyProp("test"); f.call("readMyProp", new Object[]{jb}));
The called extension file looks like this:
import mypackage; readMyProp(MyBeanMetaClass jb) : jb.myProp ;
With the additional support for model transformation, it makes sense to invoke Xtend within a workflow. A typical workflow configuration of the Xtend component looks like this:
<component class="org.eclipse.xtend.XtendComponent"> <metaModel class="org.eclipse.xtend.typesystem.emf.EmfMetaModel"> <metaModelFile value="metamodel1.ecore"/> </metamodel> <metaModel class="org.eclipse.xtend.typesystem.type.emf.EmfMetaModel"> <metaModelFile value="metamodel2.ecore"/> </metaModel> <invoke value="my::example::Trafo::transform(inputSlot)"/> <outputSlot value="transformedModel"/> </component>
Note that you can mix and use any kinds of metamodels (not only EMF metamodels).
Using the workflow engine, it is now possible to package (e.g. zip) a written generator and deliver it as a kind of black box. If you want to use such a generator but need to change some things without modifying any code, you can make use of around advices that are supported by Xtend.
The following advice is weaved around every invocation of an extension whose name starts with 'my::generator::':
around my::generator::*(*) : log('Invoking ' + ctx.name) -> ctx.proceed() ;
Around advices let you change behaviour in an non-invasive way (you do not need to touch the packaged extensions).
Aspect orientaton is basically about weaving code into different points inside the call graph of a software module. Such points are called join points. In Xtend the join points are the extension invocations (Note that Xpand offers a similar feature, see the Xpand documentation).
One specifies on which join points the contributed code should be executed by specifying something like a 'query' on all available join points. Such a query is called a point cut.
around [pointcut] : expression;
A point cut consists of a fully qualified name and a list of parameter declarations.
The extension name part of a point cut must match the fully qualified name of the definition of the join point. Such expressions are case sensitive. The asterisk character is used to specify wildcards. Some examples:
my::Extension::definition // extensions with the specified name org::eclipse::xpand2::* //extensions prefixed with 'org::eclipse::xpand2::' *Operation* // extensions containing the word 'Operation' in it. * // all extensions
![]() | |
Be careful when using wildcards, because you will get an endless recursion, in case you weave an extension, which is called inside the advice. |
The parameters of the extensions that we want to add our advice to, can also be specified in the point cut. The rule is, that the type of the specified parameter must be the same or a supertype of the corresponding parameter type (the dynamic type at runtime) of the definition to be called.
Additionally, one can set the wildcard at the end of the parameter list, to specify that there might be none or more parameters of any kind.
Some examples:
my::Templ::extension() // extension without parameters my::Templ::extension(String s) // extension with exactly one parameter of type String my::Templ::extension(String s,*) // templ def with one or more parameters, // where the first parameter is of type String my::Templ::extension(*) // templ def with any number of parameters
Inside an advice, you might want to call the underlying
definition. This can be done using the implicit variable
ctx
, which is of the type
xtend::AdviceContext and provides an operation
proceed()
which invokes the underlying definition with the
original parameters (Note that you might have changed any mutable
object in the advice before).
If you want to control what parameters are to be passed to the
definition, you can use the operation
proceed(List[Object] params)
. You should be
aware, that in advices, no type checking is done.
Additionally, there are some inspection properties (like
name
, paramTypes
, etc.)
available.
To weave the defined advices into the different join
points, you need to configure the
XtendComponent
with the qualified names of the Extension files
containing the advices.
Example:
<component class="org.eclipse.xtend.XtendComponent"> <metaModel class="org.eclipse.xtend.typesystem.emf.EmfMetaModel"> <metaModelFile value="metamodel1.ecore"/> </metamodel> <metaModel class="org.eclipse.xtend.typesystem.emf.EmfMetaModel"> <metaModelFile value="metamodel2.ecore"/> </metaModel> <invoke value="my::example::Trafo::transform(inputSlot)"/> <outputSlot value="transformedModel"/> <advices value="my::Advices,my::Advices2"/> </component>
This example uses Eclipse EMF as the basis for model-to-model transformations.
The idea in this example is to transform the data model introduced in the EMF example into itself. This might seem boring, but the example is in fact quite illustrative.
By now, you should know the role and structure of workflow
files. Therefore, the interesting aspect of the workflow file below is
the XtendComponent
.
<workflow> <property file="workflow.properties"/> ... <component class="org.eclipse.xtend.XtendComponent"> <metaModel class="org.eclipse.xtend.typesystem.emf.EmfMetaModel"> <metaModelPackage value="data.DataPackage"/> </metaModel> <invoke value="test::Trafo::duplicate(rootElement)"/> <outputSlot value="newModel"/> </component> ... </workflow>
As usual, we have to define the metamodel that should be used,
and since we want to transform a data model into a data model, we need
to specify only the data.DataPackage
as the
metamodel.
We then specify which function to invoke for the transformation.
The statement
test::Trafo::duplicate(rootElement)
means to
invoke:
the duplicate
function taking the
contents of the rootElement
slot as a
parameter
the function can be found in the
Trafo.ext
file
and that in turn is in the classpath, in the test. I hope this is what is meant here. The former text was broken XML.
The transformation, as mentioned above, can be found in the
Trafo.ext
file in the test
package in the src
folder. Let us walk through
the file.
So, first we import the metamodel.
import data;
The next function is a so-called create extension. Create extensions, as a side effect when called,
create an instance of the type given after the
create
keyword. In our case, the
duplicate
function creates an instance of
DataModel
. This newly created object can be
referred to in the transformation by this
(which is why
this
is specified behind the type). Since
this
can be omitted, we do not have to mention
it explicitly in the transformation.
The function also takes an instance of
DataModel
as its only parameter. That object is
referred to in the transformation as s
. So, this
function sets the name of the newly created
DataModel
to be the name of the original one,
and then adds duplicates of all entities of the original one to the
new one. To create the duplicates of the entities, the
duplicate()
operation is called for each
Entity
. This is the next function in the
transformation.
create DataModel this duplicate(DataModel s): entity.addAll(s.entity.duplicate()) -> setName(s.name);
The duplication function for entities is also a create
extension. This time, it creates a new Entity
for each old Entity
passed in. Again, it copies
the name and adds duplicates of the attributes and references to the
new one.
create Entity this duplicate(Entity old): attribute.addAll(old.attribute.duplicate()) -> reference.addAll(old.reference.duplicate()) -> setName(old.name);
The function that copies the attribute is rather straight forward, but ...
create Attribute this duplicate(Attribute old): setName(old.name) -> setType(old.type);
... the one for the references is more interesting. Note that a
reference, while being owned by some Entity
,
also references another Entity as its target. So, how do you make sure
you do not duplicate the target twice? Xtend
provides explicit support for this kind of situation. Create
extensions are only executed once per tuple of parameters!
So if, for example, the Entity behind the target
reference had already been duplicated by calling the
duplicate
function with the respective
parameter, the next time it will be called the exact same
object will be returned. This is very useful for graph
transformations.
create EntityReference this duplicate(EntityReference old): setName( old.name ) -> setTarget( old.target.duplicate() );
For more information about the Xtend language please see the Xtend reference documentation.
The Xpand language is used in templates to control the output generation. This documentation describes the general syntax and semantics of the Xpand language.
Typing the guillemets (« and ») used in the templates is supported by the Eclipse editor: which provides keyboard shortcuts with Ctrl+< and Ctrl+>.
Templates are stored in files with the extension
.xpt
. Template files must reside on the Java classpath of the generator
process.
Almost all characters used in the standard syntax are part of
ASCII and should therefore be available in any
encoding. The only limitation are the tag brackets
(guillemets), for which the characters "«" (Unicode
00AB
) and "»" (Unicode 00BB
) are
used. So for reading templates, an encoding should be used that supports
these characters (e.g. ISO-8859-1
or
UTF-8
).
Names of properties, templates, namespaces etc. must only contain letters, numbers and underscores.
Here is a first example of a template:
«IMPORT meta::model» «EXTENSION my::ExtensionFile» «DEFINE javaClass FOR Entity» «FILE fileName()» package «javaPackage()»; public class «name» { // implementation } «ENDFILE» «ENDDEFINE»
A template file consists of any number of IMPORT statements, followed by any number of EXTENSION statements, followed by one or more DEFINE blocks (called definitions).
If you are tired of always typing the fully qualified names of your types and definitions, you can import a namespace using the IMPORT statement.
«IMPORT meta::model»
This
one imports the namespace meta::model
. If your
template contains such a statement, you can use the unqualified names
of all types and template files contained in that namespace. This is
similar to a Java import statement import
meta.model.*
.
Metamodels are typically described in a structural way (graphical, or hierarchical, etc.) . A shortcoming of this is that it is difficult to specify additional behaviour (query operations, derived properties, etc.). Also, it is a good idea not to pollute the metamodel with target platform specific information (e.g. Java type names, packages, getter and setter names, etc.).
Extensions provide a flexible and convenient way of defining additional features of metaclasses. You do this by using the Xtend language. (See the corresponding reference documentation for details)
An EXTENSION import points to the Xtend file containing the required extensions:
«EXTENSION my::ExtensionFile»
Note that extension files have to reside on the Java classpath, too. Therefore, they use the same namespace mechanism (and syntax) as types and template files.
The central concept of Xpand is the
DEFINE
block, also called a template. This is the
smallest identifiable unit in a template file. The tag consists of a name, an optional
comma-separated parameter list, as well as the name of the metamodel
class for which the template is defined.
«DEFINE templateName(formalParameterList) FOR MetaClass» a sequence of statements «ENDDEFINE»
To some extent, templates can be seen as special
methods of the metaclass â there is always an implicit
this parameter which can be used to address the
"underlying" model element; in our example above, this model element
is "MetaClass
".
As in Java, a formal parameter list entry consists of the type followed by the name of that parameter.
The body of a template can contain a sequence of other statements including any text.
A full parametric polymorphism is available for templates. If there are two templates with the same name that are defined for two metaclasses which inherit from the same superclass, Xpand will use the corresponding subclass template, in case the template is called for the superclass. Vice versa, the template of the superclass would be used in case a subclass template is not available. Note that this not only works for the target type, but for all parameters. Technically, the target type is handled as the first parameter.
So, let us assume you have the following metamodel:
Assume further, you would have a model which contains a
collection of A
, B
and
C
instances in the property
listOfAs
. Then, you can write the following
template:
«DEFINE someOtherDefine FOR SomeMetaClass» «EXPAND implClass FOREACH listOfAs» «ENDDEFINE» «DEFINE implClass FOR A» // this is the code generated for the superclass A «ENDDEFINE» «DEFINE implClass FOR B» // this is the code generated for the subclass B «ENDDEFINE» «DEFINE implClass FOR C» // this is the code generated for the subclass C «ENDDEFINE»
So for each B
in the list,
the template defined for B
is executed, for
each C
in the collection the template defined
for C
is invoked, and for
all others (which are then instances of A
) the
default template is executed.
The FILE
statement redirects the output
generated from its body statements to the specified target.
«FILE expression [outletName]» a sequence of statements «ENDFILE»
The target is a file in the file system whose name is specified by the expression (relative to the specified target directory for that generator run). The expression for the target specification can be a concatenation (using the + operator). Additionally, you can specify an identifier (a legal Java identifier) for the name of the outlet. (See the configuration section for a description of outlets).
The body of a FILE
statement can contain any
other statements. Example:
«FILE InterfaceName + ".java"» package «InterfacePackageName»; /* generated class! Do not modify! */ public interface «InterfaceName» { «EXPAND Operation::InterfaceImplementation FOREACH Operation» } «ENDFILE» «FILE ImplName + ".java" MY_OUTLET» package «ImplPackageName»; public class «ImplName» extends «ImplBaseName» implements «InterfaceName» { //TODO: implement it } «ENDFILE»
The EXPAND
statement "expands" another
DEFINE
block (in a separate variable context),
inserts its output at the current location and continues with the next
statement. This is similar in concept to a subroutine call.
«EXPAND definitionName [(parameterList)] [FOR expression | FOREACH expression [SEPARATOR expression] ]»
The various alternative syntaxes are explained below.
If the definitionName is a simple
unqualified name, the corresponding DEFINE
block
must be in the same template file.
If the called definition is not contained in the same template file, the name of the template file must be specified. As usual, the double colon is used to delimit namespaces.
«EXPAND TemplateFile::definitionName FOR myModelElement»
Note
that you would need to import the namespace of the template file (if there is one). For instance,
if the template file resides in the java package
my.templates
, there are two alternatives. You
could either write
«IMPORT my::templates» ... «EXPAND TemplateFile::definitionName FOR myModelElement»
or
«EXPAND my::templates::TemplateFile::definitionName FOR myModelElement»
If FOR
or FOREACH
is
omitted the other template is called FOR this
.
«EXPAND TemplateFile::definitionName»
equals
«EXPAND TemplateFile::definitionName FOR this»
If FOR
is specified, the definition is executed for
the result of the target expression.
«EXPAND myDef FOR entity»
If
FOREACH
is specified, the target expression must
evaluate to a collection type. In this case, the specified definition is executed for
each element of that collection.
«EXPAND myDef FOREACH entity.allAttributes»
If a definition is to be expanded FOREACH
element of the target expression it is possible to specify a
SEPARATOR
expression:
«EXPAND paramTypeAndName FOREACH params SEPARATOR ','»
The result of the separator expression will be written to the output between each evaluation of the target definition (not after each one, but rather only in between two elements. This comes in handy for things such as comma-separated parameter lists).
An EvaluationException
will be thrown if
the specified target expression cannot be evaluated to an existing
element of the instantiated model or no suitable
DEFINE
block can be found.
This statement expands the body of the
FOREACH
block for each element of the target
collection that results from the expression. The current element
is bound to a variable with the specified name in the current context.
«FOREACH expression AS variableName [ITERATOR iterName] [SEPARATOR expression]» a sequence of statements using variableName to access the current element of the iteration «ENDFOREACH»
The body of a FOREACH
block
can contain any other statements; specifically
FOREACH
statements may be nested. If
ITERATOR
name is specified, an object of the type
xpand2::Iterator (see API doc for details) is
accessible using the specified name. The SEPARATOR
expression works in the same way as the one for
EXPAND
.
Example:
«FOREACH {'A','B','C'} AS c ITERATOR iter SEPARATOR ','» «iter.counter1» : «c» «ENDFOREACH»
The evaluation of the above statement results in the following text:
1 : A, 2 : B, 3 : C
The IF
statement supports conditional
expansion. Any number of ELSEIF
statements are allowed. The ELSE
block is optional. Every IF
statement must be
closed with an ENDIF
. The body of an IF
block can contain
any other statement, specifically, IF
statements
may be nested.
«IF expression» a sequence of statements [ «ELSEIF expression» ] a sequence of statements ] [ «ELSE» a sequence of statements ] «ENDIF»
Protected Regions are used to mark sections in the generated code that shall not be overridden again by the subsequent generator run. These sections typically contain manually written code.
«PROTECT CSTART expression CEND expression ID expression (DISABLE)?» a sequence of statements «ENDPROTECT»
The values of CSTART and CEND expressions are used to enclose the protected regions marker in the output. They should build valid comment beginning and end strings corresponding to the generated target language (e.g. "/*" and "*/" for Java). The following is an example for Java:
«PROTECT CSTART "/*" CEND "*/" ID ElementsUniqueID» here goes some content «ENDPROTECT»
The ID is set by the ID
expression and must be globally unique (at least for one complete pass
of the generator).
Generated target code looks like this:
public class Person { /*PROTECTED REGION ID(Person) ENABLED START*/ This protected region is enabled, therefore the contents will always be preserved. If you want to get the default contents from the template you must remove the ENABLED keyword (or even remove the whole file :-)) /*PROTECTED REGION END*/ }
Protected regions are generated in enabled state by default. Unless you manually disable them, by removing the ENABLED
keyword, they will always be preserved.
If you want the generator to generate disabled protected
regions, you need to add the DISABLE
keyword inside
the declaration:
«PROTECT CSTART '/*' CEND '*/' ID this.name DISABLE»
LET
lets you specify local
variables:
«LET expression AS variableName» a sequence of statements «ENDLET»
During the expansion of the body of the
LET
block, the value of the expression is bound to the
specified variable. Note that the expression will only be evaluated
once, independent from the number of usages of the variable within the
LET
block. Example:
«LET packageName + "." + className AS fqn» the fully qualified name is: «fqn»; «ENDLET»
The ERROR
statement aborts the evaluation of
the templates by throwing an
XpandException
with the specified message.
«ERROR expression»
Note that you should use this facility very sparingly, since it is better practice to check for invalid models using constraints on the metamodel, and not in the templates.
Comments are only allowed outside of tags.
«REM» text comment «ENDREM»
Comments may not contain a REM tag, this implies that comments are not nestable. A comment may not have a white space between the REM keyword and its brackets. Example:
«REM»«LET expression AS variableName»«ENDREM» a sequence of statements «REM» «variableName.stuff» «ENDLET»«ENDREM»
Expressions support processing of the information provided by
the instantiated metamodel. Xpand provides powerful expressions for
selection, aggregation, and navigation. Xpand uses the expressions
sublanguage in almost any statement that we have seen so far. The
expression statement just evaluates the contained expression and
writes the result to the output (using the
toString()
method of
java.lang.Object
). Example:
public class «this.name» {
All expressions defined by the oArchitectureWare expressions sublanguage are also available in Xpand. You can invoke imported extensions. (See the Expressions and Xtend language reference for more details).
If you want to omit the output of superfluous whitespace you can add a minus sign just before any closing bracket. Example:
«FILE InterfaceName + ".java"-» «IF hasPackage-» package «InterfacePackageName»; «ENDIF-» ... «ENDFILE»
The generated file would start with two new lines
(one after the FILE
and one after the
IF
statement) if the minus characters had not been
set.
In general, this mechanism works as follows: If a statement (or comment) ends with such a minus all preceding whitespace up to the newline character (excluded!) is removed. Additionally all following whitespace including the first newline character (\r\n is handled as one character) is also removed.
Using the workflow engine it is now possible to package
(e.g. zip) a written generator and deliver it as a
kind of black box. If you want to use such a generator but need to
change some small generation stuff, you can make use of the
AROUND
aspects.
«AROUND qualifiedDefinitionName(parameterList)? FOR type» a sequence of statements «ENDAROUND»
AROUND
lets you add templates
in an non-invasive way (you do not need to touch the generator
templates). Because aspects are invasive, a template file containing
AROUND
aspects must be wrapped by configuration (see
next section).
AOP is basically about weaving code into different points inside the call graph of a software module. Such points are called Join Points. In Xpand, there is only one join point so far: a call to a definition.
You specify on which join points the contributed code should be executed by specifying something like a 'query' on all available join points. Such a query is called a point cut.
«AROUND [pointcut]» do stuff «ENDAROUND»
A pointcut consists of a fully qualified name, parameter types and the target type.
The definition name part of a point cut must match the fully qualified name of the join point definition. Such expressions are case sensitive. The asterisk character is used to specify wildcards.
Some examples:
my::Template::definition // definitions with the specified name org::eclipse::xpand2::* // definitions prefixed with 'org::eclipse::xpand2::' *Operation* // definitions containing the word 'Operation' in it. * // all definitions
The parameters of the definitions we want to add our advice to, can also be specified in the point cut. The rule is that the type of the specified parameter must be the same or a supertype of the corresponding parameter type (the dynamic type at runtime!) of the definition to be called.
Additionally, one can set a wildcard at the end of the parameter list, to specify that there might be an arbitrary number of parameters of any kind.
Some examples:
my::Templ::def() // templ def without parameters my::Templ::def(String s) // templ def with exactly one parameter // of type String my::Templ::def(String s,*) // templ def with one or more parameters, // where the first parameter is of type String my::Templ::def(*) // templ def with any number of parameters
Inside an advice, you might want to call the underlying
definition. This can be done using the implicit variable
targetDef
, which is of the type
xpand2::Definition and which provides an operation
proceed()
that invokes the underlying
definition with the original parameters (Note that you might have
changed any mutable object in the advice before).
If you want to control, what parameters are to be passed to the
definition, you can use the operation
proceed
(Object
target
, List
params
). Please keep in mind that no type checking
is done in this context.
Additionally, there are some inspection properties (like
name
, paramTypes
, etc.)
available.
This section describes the workflow component that is provided to perform the code generation, i.e. run the templates. You should have a basic idea of how the workflow engine works. A simple generator component configuration could look as follows:
<component class="org.eclipse.xpand2.Generator"> <fileEncoding value="ISO-8859-1"/> <metaModel class="org.eclipse.xtend.typesystem.emf.EmfMetaModel"> <metaModelPackage value="org.eclipse.emf.ecore.EcorePackage"/> </metaModel> <expand value="example::Java::all FOR myModel"/> <!-- aop configuration --> <advices value='example::Advices1, example::Advices2'/> <!-- output configuration --> <outlet path='main/src-gen'/> <outlet name='TO_SRC' path='main/src' overwrite='false'/> <beautifier class="org.eclipse.xpand2.output.JavaBeautifier"/> <beautifier class="org.eclipse.xpand2.output.XmlBeautifier"/> <!-- protected regions configuration --> <prSrcPaths value="main/src"/> <prDefaultExcludes value="false"/> <prExcludes value="*.xml"/> </component>
Now, let us go through the different properties one by one.
The first thing to note is that the qualified Java name of the
component is
org.eclipse.xpand2.Generator
.
For Xpand, it is important to have the file
encoding in mind because of the
guillemet characters used to delimit keywords and property access. The
fileEncoding
property specifies the file encoding to use for reading the
templates, reading the protected regions and writing the generated
files. This property defaults to the default file encoding of your
JVM.
The property metaModel
is used to tell the generator engine on which
metamodels the Xpand templates should be
evaluated. One can specify more than one metamodel here. Metamodel
implementations are required by the expression framework (see
Expressions) used
by Xpand2. In the example above we configured the
Ecore metamodel using the EMFMetaModel
implementation shipped with the core part of the Xpand release.
A mandatory configuration is the expand
property. It expects a syntax similar to that of the
EXPAND
statement (described above). The only
difference is that we omit the EXPAND
keyword. Instead, we specify the name of the property.
Examples:
<expand value="Template::define FOR mySlot"/>
or:
<expand value="Template::define('foo') FOREACH {mySlot1,mySlot2}"/>
The
expressions are evaluated using the workflow context. Each slot is
mapped to a variable. For the examples above the workflow context
needs to contain elements in the slots 'mySlot'
,
'mySlot1'
and 'mySlot2'
. It is
also possible to specify some complex expressions here. If, for
instance, the slot myModel
contains a collection of
model elements one could write:
<expand value="Template::define FOREACH myModel.typeSelect(Entity)"/>
This
selects all elements of type Entity contained in
the collection stored in the myModel
slot.
The second mandatory configuration is the specification of so called outlets (a concept borrowed from AndroMDA). Outlets are responsible for writing the generated files to disk. Example:
<component class="org.eclipse.xpand2.Generator2"> ... <outlet path='main/src-gen'/> <outlet name='TO_SRC' path='main/src' overwrite='false'/> ... </component>
In the example there are two outlets configured. The first one has no name and is therefore handled as the default outlet. Default outlets are triggered by omitting an outlet name:
«FILE 'test/note.txt'» # this goes to the default outlet «ENDFILE»
The configured base path is
'main/src-gen
', so the file from above would go
to 'main/src-gen/test/note.txt
'.
The second outlet has a name
('TO_SRC')
specified. Additionally the flag overwrite
is set
to false
(defaults to true
). The
following Xpand fragment
«FILE 'test/note.txt' TO_SRC» # this goes to the TO_SRC outlet «ENDFILE»
would cause the generator to write the contents to
'main/src/test/note.txt
' if the file does not
already exist (the overwrite
flag).
Another option called append
(defaults to
false
) causes the generator to append the generated
text to an existing file. If overwrite
is set to
false
this flag has no effect.
Beautifying the generated code is a good idea. It is very important that generated code looks good, because developers should be able to understand it. On the other hand template files should look good, too. It is thus best practice to write nice looking template files and not to care how the generated code looks â and then you run a beautifier over the generated code to fix that problem. Of course, if a beautifier is not available, or if white space has syntactical meaning (as in Python), you would have to write your templates with that in mind (using the minus character before closing brackets as described in a preceding section).
The Xpand workflow component can be configured with multiple beautifiers:
<beautifier class="org.eclipse.xpand2.output.JavaBeautifier"/> <beautifier class="org.eclipse.xpand2.output.XMLBeautifier"/>
These
are the two beautifiers delivered with Xpand. If
you want to use your own beautifier, you would just need to implement
the PostProcessor
Java interface:
package org.eclipse.xpand2.output; public interface PostProcessor { public void beforeWriteAndClose(FileHandle handle); public void afterClose(FileHandle handle); }
The beforeWriteAndClose
method is called
for each ENDFILE
statement.
Finally, you need to configure the protected region resolver, if you want to use protected regions.
<prSrcPaths value="main/src"/> <prDefaultExcludes value="false"/> <prExcludes value="*.xml"/>
The prSrcPaths property points to a comma-separated list of directories. The protected region resolver will scan these directories for files containing activated protected regions.
There are several file names which are excluded by default:
RCS, SCCS, CVS, CVS.adm, RCSLOG, cvslog.*, tags, TAGS, .make.state, .nse_depinfo, *~, #*, .#*, ',*', _$*,*$, *.old, *.bak, *.BAK, *.orig, *.rej, .del-*, *.a, *.olb, *.o, *.obj, *.so, *.exe, *.Z,* .elc, *.ln, core, .svn
If you do not want
to exclude any of these, you must set
prDefaultExcludes
to false.
<prDefaultExcludes value="false"/>
If you want to add additional excludes, you should use the prExcludes property.
<prExcludes value="*.xml,*.hbm"/>
![]() | |
It is bad practice to mix generated and non-generated code in one artifact. Instead of using protected regions, you should try to leverage the extension features of the used target language (inheritance, inclusion, references, etc.) wherever possible. It is very rare that the use of protected regions is an appropriate solution. |
The Xpand engine will generate code for each processed FILE statement. This implies that files are written that might not have changed to the previous generator run. Normally it does not matter that files are rewritten. There are at least two good reasons when it is better to avoid rewriting of files:
The generated source code will be checked in. In general it is not the recommended way to go to check in generated code, but sometimes you will have to. Especially with CVS there is the problem that rewritten files are recognized as modified, even if they haven't changed. So the problem arises that identical files get checked in again and again (or you revert it manually). When working in teams the problem even becomes worse, since team members will have conflicts when checking in.
When it can be predicted that the generator won't produce different content before a file is even about to be created by a FILE statement then this can boost performance. Of course it is not trivial to predict that a specific file won't result in different content before it is even created. This requires information from a prior generator run and evaluation against the current model to process. Usually a diff model would be used as input for the decision.
Case 1) will prevent file writing after a FILE statement has been evaluated, case 2) will prevent creating a file at all.
To achieve this it is possible to add Veto Strategies to the
generator, which are implementations of interface
org.eclipse.xpand2.output.VetoStrategy
or
org.eclipse.xpand2.output.VetoStrategy2
.
Use VetoStrategy2
if you implement your
own.
VetoStrategy2
declares two
methods:
boolean hasVetoBeforeOpen
(FileHandle)
This method will be called before a file is being opened and generated. Return true to suppress the file creation.
boolean hasVeto (FileHandle)
This method will be called after a file has been produced and after all configured PostProcessors have been invoked. Return true to suppress writing the file.
Veto Strategies are configured per Outlet. It is possible to add multiple stratgy instances to each Outlet.
<component id="generator" class="org.eclipse.xpand2.Generator" skipOnErrors="true">
<metaModel class="org.eclipse.xtend.typesystem.uml2.UML2MetaModel"/>
<expand value="templates::Root::Root FOR model"/>
<fileEncoding value="ISO-8859-1"/>
<outlet path="src-gen">
<postprocessor class="org.eclipse.xpand2.output.JavaBeautifier"/>
<vetoStrategy class="org.eclipse.xpand2.output.NoChangesVetoStrategy"/>
</outlet>
</component>
One VetoStrategy
is already provided.
The
org.eclipse.xpand2.output.NoChangesVetoStrategy
is a simple implementation that will compare the
produced output, after it has been postprocessed, with the target
file. If the content is identical the strategy vetoes the file
writing. This strategy is effective, but has two severe
drawbacks:
The file has been created at least in memory before. This consumes time and memory. If applying code formatting this usually implies that the file is temporarily written.
The existing file must be read into memory. This also costs time and memory.
Much better would be to even prevent the creation of files by
having a valid implementation for the
hasVetoBeforeOpen()
method. Providing an
implementation that predicts that files do not have to be created
requires domain knowledge, thus a standard implementation is not
available.
The number of skipped files will be reported by the Generator component like this:
2192 INFO - Generator(generator): generating <...>
3792 INFO - Skipped writing of 2 files to outlet [default](src-gen)
This example shows how to use aspect-oriented programming techniques in Xpand templates. It is applicable to EMF based and Classic systems. However, we explain the idea based on the emfExample â hence you should read that before.
There are many circumstances when template-AOP is useful. Here are two examples:
Scenario 1: Assume you have a nice generator that generates certain artifacts. The generator (or cartridge) might be a third party product, delivered in a single JAR file. Still you might want to adapt certain aspects of the generation process â without modifying the original generator.
Scenario 2: You are building a family of generators that can generate variations of the generate code, e.g. Implementations for different embedded platforms. In such a scenario, you need to be able to express those differences (variabilities) sensibly without creating a non-understandable chaos of if statements in the templates.
To illustrate the idea of extending a generator without "touching"
it, let us create a new project called
org.eclipse.demo.emf.datamodel.generator-aop
. The idea
is that it will "extend" the original
org.eclipse.demo.emf.datamodel.generator
project
introduced in the emfExample. So this new projects
needs to have a project dependency to the former one.
An AOP system always needs to define a join point model; this is, you have to define, at which locations
of a (template) program you can add additional (template) code. In
Xpand, the join points are simply templates (i.e. DEFINE ..
ENDDEFINE) blocks. An "aspect template" can be declared
AROUND previously existing templates. If you take a look at
the org.eclipse.demo.emf.datamodel.generator
source
folder of the project, you can find the Root.xpt
template file. Inside, you can find a template called
Impl
that generates the implementation of the
JavaBean.
«DEFINE Entity FOR data::Entity» «FILE baseClassFileName() » // generated at «timestamp()» public abstract class «baseClassName()» { «EXPAND Impl» } «ENDFILE» «ENDDEFINE» «DEFINE Impl FOR data::Entity» «EXPAND GettersAndSetters» «ENDDEFINE» «DEFINE Impl FOR data::PersistentEntity» «EXPAND GettersAndSetters» public void save() { } «ENDDEFINE»
What we now want to do is as follows: Whenever the Impl template is executed, we want to run an additional template that generates additional code (for example, some kind of meta information for frameworks â the specific code is not important for the example here).
So, in our new project, we define the following template file:
«AROUND Impl FOR data::Entity» «FOREACH attribute AS a» public static final AttrInfo «a.name»Info = new AttrInfo( "«a.name»", «a.type».class ); «ENDFOREACH» «targetDef.proceed()» «ENDAROUND»
So, this new template wraps around the existing template called
Impl
It first generates additional code and
then forwards the execution to the original template using
targetDef.proceed()
. So, in effect, this is a
BEFORE
advice. Moving the
proceed
statement to the beginning makes it
an AFTER
advice, omitting it, makes it an
override.
Let us take a look at the workflow file to run this generator:
<workflow> <cartridge file="workflow.mwe"/> <component adviceTarget="generator" id="reflectionAdvice" class="org.eclipse.xpand2.GeneratorAdvice"> <advices value="templates::Advices"/> </component> </workflow>
Mainly, what we do here, is to call the original workflow file.
It has to be available from the classpath. After this cartridge call,
we define an additional workflow component, a so called
advice component. It specifies
generator as its
adviceTarget. That means, that all the properties
we define inside this advice component will be added to the component
referenced by name in the adviceTarget instead.
In our case, this is the generator. So, in effect, we add the
<advices value="templates::Advices" />
to
the original generator component (without invasively modifying its own
definition). This contributes the advice templates to the
generator.
Running the generator produces the following code:
public abstract class PersonImplBase { public static final AttrInfo nameInfo = new AttrInfo("name", String.class); public static final AttrInfo name2Info = new AttrInfo("name2", String.class); private String name; private String name2; public void setName(String value) { this.name = value; } public String getName() { return this.name; } public void setName2(String value) { this.name2 = value; } public String getName2() { return this.name2; } }
In general, the syntax for the AROUND construct is as follows:
<<AROUND fullyQualifiedDefinitionNameWithWildcards (Paramlist (*)?) FOR TypeName>> do Stuff <<ENDAROUND>>
Here are some examples:
<<AROUND *(*) FOR Object>>
matches all templates
<<AROUND *define(*) FOR Object>>
matches all templates with define at the end of its name and any number of parameters
<<AROUND org::eclipse::xpand2::* FOR Entity>>
matches all templates with namespace org::eclipse::xpand2:: that do not have any parameters and whose type is Entity or a subclass
<<AROUND *(String s) FOR Object>>
matches all templates that have exactly one
String
parameter
<<AROUND *(String s,*) FOR Object>>
matches all templates that have at least one
String
parameter
<<AROUND my::Template::definition(String s) FOR Entity>>
matches exactly this single definition
Inside an AROUND
, there is the variable
targetDef
, which has the type
xpand2::Definition
. On this variable, you can
call proceed
, and also query a number of other
things:
<<AROUND my::Template::definition(String s) FOR String>> log('invoking '+<<targetDef.name>>+' with '+this) <<targetDef.proceed()>> <<ENDAROUND>>
Supertype: none
Table 2.2. Operations
Return type | Name | Description |
---|---|---|
Boolean
|
==
(Object )
| |
Boolean
|
<
(Object )
| |
String
|
toString
()
| returns the String representation of this object. (Calling Java's toString() method) |
Boolean
|
<=
(Object )
| |
Boolean
|
!=
(Object )
| |
Boolean
|
>
(Object )
| |
Integer
|
compareTo
(Object )
| Compares this object with the specified object for order. Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object. |
Boolean
|
>=
(Object )
|
Supertype:
Object
Table 2.4. Operations
Return type | Name | Description |
---|---|---|
String
|
toLowerCase
()
| Converts all of the characters in this String to lower case using the rules of the default locale (from Java) |
String
|
+
(Object )
| concatenates two strings |
List
|
toCharList
()
| splits this String into a List[String] containing Strings of length 1 |
String
|
toFirstUpper
()
| Converts the first character in this String to upper case using the rules of the default locale (from Java) |
String
|
subString
(Integer , Integer )
| Returns a new string that is a substring of this string. |
String
|
trim
()
| Returns a copy of the string, with leading and trailing whitespace omitted. (from Java 1.4) |
String
|
toFirstLower
()
| Converts the first character in this String to lower case using the rules of the default locale (from Java) |
String
|
toUpperCase
()
| Converts all of the characters in this String to upper case using the rules of the default locale (from Java) |
List
|
split
(String )
| Splits this string around matches of the given regular expression (from Java 1.4) |
Boolean
|
startsWith
(String )
| Tests if this string starts with the specified prefix. |
Boolean
|
matches
(String )
| Tells whether or not this string matches the given regular expression. (from Java 1.4) |
Integer
|
asInteger
()
| Returns an Integer object holding the value of the specified String (from Java 1.5) |
Boolean
|
contains
(String )
| Tests if this string contains substring. |
Boolean
|
endsWith
(String )
| Tests if this string ends with the specified prefix. |
String
|
replaceFirst
(String , String )
| Replaces the first substring of this string that matches the given regular expression with the given replacement. |
String
|
replaceAll
(String , String )
| Replaces each substring of this string that matches the given regular expression with the given replacement. |
Supertype:
Real
This type does not define any properties.
Table 2.5. Operations
Return type | Name | Description |
---|---|---|
List
|
upTo
(Integer )
| returns a List of Integers starting with the value of the target expression, up to the value of the specified Integer, incremented by one.<br></br>e.g. '1.upTo(5)' evaluates to {1,2,3,4,5} |
Boolean
|
>=
(Integer )
| |
Boolean
|
==
(Integer )
| |
Boolean
|
!=
(Integer )
| |
List
|
upTo
(Integer , Integer )
| returns a List of Integers starting with the value of the target expression, up to the value of the first paramter, incremented by the second parameter.<br></br>e.g. '1.upTo(10, 2)' evaluates to {1,3,5,7,9} |
Integer
|
-
(Integer )
| |
Integer
|
+
(Integer )
| |
Boolean
|
<=
(Integer )
| |
Boolean
|
<
(Integer )
| |
Integer
|
*
(Integer )
| |
Integer
|
-
()
| |
Boolean
|
>
(Integer )
| |
Integer
|
/
(Integer )
|
Supertype:
Object
Table 2.9. Operations
Return type | Name | Description |
---|---|---|
Boolean
|
contains
(Object )
| returns true if this collection contains the specified object. otherwise false. returns this Collection. |
List
|
toList
()
| converts this collection to List |
Set
|
toSet
()
| converts this collection to Set |
List
|
flatten
()
| returns a flattened List. |
Set
|
intersect
(Collection )
| returns a new Set, containing only the elements contained in this and the specified Collection |
String
|
toString
(String )
| concatenates each contained element (using toString()), separated by the specified String. |
Collection
|
removeAll
(Object )
| removes all elements contained in the specified collection from this Collection if contained (modifies it!). returns this Collection. |
Collection
|
remove
(Object )
| removes the specified element from this Collection if contained (modifies it!). returns this Collection. |
Set
|
without
(Collection )
| returns a new Set, containing all elements from this Collection without the elements from specified Collection |
Collection
|
addAll
(Collection )
| adds all elements to the Collection (modifies it!). returns this Collection. |
Collection
|
add
(Object )
| adds an element to the Collection (modifies it!). returns this Collection. |
Set
|
union
(Collection )
| returns a new Set, containing all elements from this and the specified Collection |
Boolean
|
containsAll
(Collection )
| returns true if this collection contains each element contained in the specified collection. otherwise false. returns this Collection. |
Supertype:
Collection
This type does not define any properties.
This type does not define any operations.
Supertype:
Object
Table 2.12. Operations
Return type | Name | Description |
---|---|---|
xpand2::StaticProperty
|
getStaticProperty
(String )
| |
xpand2::Feature
|
getFeature
(String , List )
| |
Boolean
|
isInstance
(Object )
| |
xpand2::Property
|
getProperty
(String )
| |
Object
|
newInstance
()
| |
Boolean
|
isAssignableFrom
(xpand2::Type )
| |
xpand2::Operation
|
getOperation
(String , List )
|
Supertype:
Object
Table 2.13. Properties
Type | Name | Description |
---|---|---|
String
|
name
| |
xpand2::Type
|
returnType
| |
String
|
documentation
| |
xpand2::Type
|
owner
|
This type does not define any operations.
Supertype:
Object
This type does not define any properties.
This type does not define any operations.
Supertype:
Object
Table 2.19. Properties
Type | Name | Description |
---|---|---|
List
|
paramTypes
| |
String
|
name
| |
List
|
paramNames
| |
xpand2::Type
|
targetType
|
This tutorial shows how XML and XML Schemas Definitions (XSD) can be used to generate software. It illustrates how XML files are treated as models, XSDs as meta models and how this integrates with oAW. This tutorial is an introduction, for in-depth details see Chapter 4, XSD Adapter.
XSD support for oAW comes with oAW 4.3.1 or later. Make sure the following plugins are installed as well:
XSD - XML Schema Definition Runtime ( http://www.eclipse.org/xsd/, available via Ganymede Update Site)
Web Tools Platform (WTP) (WTP is not required to use oAW XSD support, but helpful, as its provides a nice XML Schema editor and a schema-aware XML editor. (http://www.eclipse.org/webtools/ , available via Ganymede Update Site)
This tutorial explains how you can do code generation with Xtend and Xpand, using XML Schema Definitions as meta models and XML files as models. To keep things easy, the introduced example is a minimalistic one. A text file is generated from contents specified in XML. The general concept of models, meta models and why and when code generation is useful, is not explained. At the end, a deeper view under the hood is taken to understand how XML Schemas are transformed to EMF Ecore models, and which flexibilities/restrictions this approach provides.
All source files listed within this tutorial are also available as
an example project wich can be imported into the Eclipse workspace by
running "File" / "New" / "Example..." / "Xpand/Xtend
Examples using an XSD Meta Model" / "M2T custom XML to Text via Xpand
(minimal Example)". This will create the project
org.eclipse.xpand.examples.xsd.m2t.minimal
project in your workspace. This minimal example is based on "M2T
custom XML to Java via Xpand"
(org.eclipse.xpand.examples.xsd.m2t.xml2javawizard
)
which is more comprehensive and recommended for further reading.
To generate code from XML files with oAW, at least files of the following four types are needed:
Meta Model ( metamodel.xsd
)
Model ( model.xml
)
oAW Xpand Template ( template.xpt
)
oAW Workflow ( workflow.oaw
)
To create a Project, create an ordinary Xtend/Xpand-Project. This is done in Eclipse by changing to the Xtend/Xpand perspective and clicking on "File" / "New" / "Xtend/Xpand Project". After entering a name for the project it is created.
After the project is created, support for XSD meta models needs to be activated. Click with your right mouse button on the project and open the properties window. Then go to the "Xpand/Xtend" page, "enable project specific settings" and activate the "XSD Metamodels" checkbox. There is no need to leave support for any other meta models activated, except you are sure that you want to use one of them, too. Figure 3.2, “Activate XSD Meta Model Support for Project” shows how the configuration is supposed to look like.
Then, org.eclipse.xtend.typesystem.xsd
needs to
be added to the project's dependencies. To do so open the file
META-INF/MANIFEST.MF
from your project and navigate
to the "Dependencies"-tab.
org.eclipse.xtend.typesystem.xsd
needs to be added to
the list of "Required Plug-ins", as it is shown in Figure 3.3, “Required Dependencies for Project” .
In case you are not going to use an existing XML Schema Definition, you can create a new a new one like described below. These steps make use of the Eclipse Web Tools Platform (WTP) to have fancy editors.
In Eclipse, click on "File", "New", "Other..." and choose "XML Schema" from category "XML". Select the project's "src" folder and specify a filename. Clicking on "finish" creates an empty XSD file. It is important that the XSD file is located somewhere within the project's classpath.
This XML Schema consists of two complex data types, which contain some elements and attributes. "complex" in the XSD terminology means that as opposed to simple data types that they can actually have sub-elements and/or attributes. This example is too minimalistic to do anything useful.
The complex Type Wizard
contains the elements
startpage
, name
,
welcometext
, and choicepage
. Except for choicepage
all elements have to
contain strings, whereas the string of startpage
must be a valid id of any ChoicePage
. The complex
type ChoicePage
just contains an
id
and a name
. For oAW it
does not make any difference if something is modeled as an XML-attribute
or XML-element. Just the datafield's type defines how oAW treats the
value.
To get an overview how schemas can be used by the oAW XSD Adapter, see the section called “How to declare XML Schemas”
Internally, the oAW XSD Adapter transforms the XSD model to an Ecore model which oAW can use like any other Ecore model. For more information about that, see the section called “Behind the scenes: Transforming XSD to Ecore”
<?xml version="1.0" encoding="UTF-8"?> <schema xmlns="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.example.org/wizard" xmlns:tns="http://www.example.org/wizard" elementFormDefault="qualified"> <complexType name="Wizard"> <sequence> <element name="startpage" type="IDREF" /> <element name="name" type="string" /> <element name="welcometext" type="string" /> <element name="choicepage" type="tns:ChoicePage" /> </sequence> </complexType> <complexType name="ChoicePage"> <sequence> <element name="title" type="string" /> </sequence> <attribute name="id" type="ID" /> </complexType> <element name="wizard" type="tns:Wizard" /> </schema>
As the title says, data in XML-Format will be the model. And as a model has to be valid according to a meta model, the XML files must be valid according to the XSD.
In case you are not going to use an existing XML file, you can create a new one like described below. These steps require the Eclipse Web Tools Platform (WTP) to be installed.
In Eclipse, click on "File", "New", "Other..." and choose "XML" from category "XML". After specifying a filename within folder "src" choose "create XML file from an XML Schema" and select you XML Schema Definition file. Telling Eclipse which schema to use has three advantages: Eclipse validates XML files, there is meta model aware code completion while editing and Eclipse creates a xsi:schemaLocation-attribute which tells anyone who reads the XML file where the schema file is located. This tutorial does not use the xsi:schemaLocation-attribute and introduces the schema file in the oAW workflow instead. For all possible ways see the section called “How to declare XML Schemas” . It is important that the XML file is located somewhere within the project's classpath.
<?xml version="1.0" encoding="UTF-8"?> <wizard xmlns="http://www.example.org/wizard"> <startpage>start</startpage> <name>My Example Setup</name> <welcometext>Welcome to this little demo application.</welcometext> <choicepage id="start"> <title>Wizard Page One</title> </choicepage> </wizard>
Create an ordinary oAW Xpand file: Being in the Xpand/Xtend perspective, go to "File", "New", "xPand template". The Xpand language itself is explained by several other oAW documents. Having XSD meta model support activated like described in the section called “Step 1: Create a Project” , oAW scans and watches all it's projects for suitable meta models. Based on what is found, the Xpand editor provides meta model aware code completion.
This example imports "metamodel
" at the
beginning, which refers to a file called
metamodel.xsd
that you have created within the
project's classpath in the section called “Step 2: Define a Meta Model using XML Schema” . The
define-block can be understood as a function named
"Root
" which takes one object of type
metamodel::Wizard
as a parameter. This is the meta
model's type for the XML's root object. The file-block creates a file
named wizard.txt
and writes the text that is
surrounded by the file-block into the file. name
,
welcometext
and
choicepage.title
are elements or attributes defined
in the XSD meta model. Their values are stored within the XML file and
this templates inserts them into the generated (
wizard.txt
) file.
«IMPORT metamodel» «DEFINE Root FOR metamodel::Wizard» «FILE "wizard.txt"» Name: «name» Welcometext: «welcometext» First Page Title: «choicepage.title» «ENDFILE» «ENDDEFINE»
The workflow ties together model, meta model and templates and defines the process of how to generate code.
To create a new workflow file, switch to the Xpand/Xtend perspective, click on "File", "New" and "Workflow file". After specifying a folder and a filename an empty workflow is created.
The minimalistic approach consists of two steps:
Read the Model: This is done by
org.eclipse.xtend.typesystem.xsd.XMLReader
. It needs exactly
one uri
element which defines the XML file. A
further nested element of type
org.eclipse.xtend.typesystem.xsd.XSDMetaModel
tells the
XMLReader
which metamodel to use.
XSDMetaModel
can contain multiple
schemaFile
elements. How the schemas are used
for the XML file is determined based on the declared namespaces.
modelSlot
defines a location where the model is
stored internally, this is like a variable name which becomes
important if you want to handle multiple models within the same
workflow.
Generate Code: This part just does the regular code generation
using Xpand and is not specific to the oAW XSD Adapter at all. The
generator org.eclipse.xpand2.Generator
needs to know which meta model to use. This example
references the previously declared one. The
expand
element tells the generator to call the
definition named Root
within file
template.xpt
using the contents of slot
model
as parameter. Element
outlet
defines where to store the generates
files.
<workflow> <component class="org.eclipse.xtend.typesystem.xsd.XMLReader"> <modelSlot value="model" /> <uri value="model.xml" /> <metaModel id="mm" class="org.eclipse.xtend.typesystem.xsd.XSDMetaModel"> <schemaFile value="metamodel.xsd" /> </metaModel> </component> <component class="org.eclipse.xpand2.Generator"> <metaModel idRef="mm" /> <expand value="template::Root FOR model" /> <outlet path="src-gen" /> </component> </workflow>
Before you actually execute the workflow, or in case of errors, you can use Figure 3.5, “Files of this Tutorial” to double check your files.
To execute the workflow, click with your right mouse button on the workflow file and choose "Run As", "oAW Workflow", as it is shown in the section called “Step 6: Execute Workflow aka Generate Code” .
When executing the workflow, this output is supposed to appear in Eclipse's Console View. If that View does not pop up automatically, you can reach it via "Window", "Show View", "Console".
May 25, 2009 3:09:35 PM org.eclipse.emf.mwe.core.WorkflowRunner prepare INFO: running workflow: /Users/meysholdt/Eclipse/workspace-3.5-M7/org.eclipse.xpand.examples.xsd.m2t.minimal/src/xsd/m2t/minimal/minimal.oaw May 25, 2009 3:09:35 PM org.eclipse.emf.mwe.core.WorkflowRunner prepare INFO: May 25, 2009 3:09:36 PM org.eclipse.xtend.typesystem.xsd.XSDMetaModel addSchemaFile INFO: Loading XSDSchema from 'xsd/m2t/minimal/metamodel.xsd' May 25, 2009 3:09:37 PM org.eclipse.xtend.typesystem.xsd.builder.OawXSDEcoreBuilder initEPackage INFO: Creating EPackage 'metamodel' from XSDSchema 'file:/.../bin/xsd/m2t/minimal/metamodel.xsd' (http://www.example.org/wizard) May 25, 2009 3:09:37 PM org.eclipse.emf.mwe.core.container.CompositeComponent internalInvoke INFO: XMLReader: Loading XML file xsd/m2t/minimal/model.xml May 25, 2009 3:09:37 PM org.eclipse.emf.mwe.core.container.CompositeComponent internalInvoke INFO: Generator: generating 'xsd::m2t::minimal::template::Root FOR model' => src-gen May 25, 2009 3:09:38 PM org.eclipse.xpand2.Generator invokeInternal2 INFO: Written 1 files to outlet [default](src-gen) May 25, 2009 3:09:38 PM org.eclipse.emf.mwe.core.WorkflowRunner executeWorkflow INFO: workflow completed in 657ms!
After code generation, there is a file called
wizard.txt
within the src-gen
folder. Its contents is supposed to look like shown below. You should be
able to recognize the structure you've defined within the template file
and the contents from your XML model.
Name: My Example Setup Welcometext: Welcome to this little demo application. First Page Title: Wizard Page One
The XSD Adapter allows oAW to read/write XML files as models and to use XML Schemas (XSDs) as meta models. This reference provides in-depth details, for a quick and pragmatic introduction see Chapter 3, XSD Tutorial .
Please take a look at the section called “Setup”.
The XSD Adapter performs two major tasks:
It converts XML Schemas (XSDs) to Ecore models in a transparent manner, so that the Ecore models are hidden from the user. This is done in the workflow as well as in the IDE (to allow XSD-aware code completion for Xtend/Xpand/Check). For details about the mapping see the section called “Behind the scenes: Transforming XSD to Ecore” . For details about the workflow integration see the section called “Workflow Components”
It extends the EmfMetaModel with concepts that are needed for XSDs. Theses are, for example, support for feature maps (needed to handle comments, nested text, CDATA and processing instructions), QNames, EMaps and composed Simpletypes.
The XSD Adapter provides the following workflow components:
The XSDMetaModel loads the specified XSD, transforms them to Ecore
models and makes them available for the other oAW components. If XSDs
include/import other XSDs or if XML files reference XSDs via
schemaLocation, theses XSDs are also loaded
(details: the section called “How to declare XML Schemas” ). The most
common scenario is to declare the XSDMetaModel
within an XMLReader
:
<component class="org.eclipse.xtend.typesystem.xsd.XMLReader"> <modelSlot value="model" /> <uri value="model.xml" /> <metaModel id="mm" class="org.eclipse.xtend.typesystem.xsd.XSDMetaModel"> <schemaFile value="metamodel.xsd" /> <registerPackagesGlobally value="true" /> </metaModel> </component>
Another option is to specify an
XSDMetaModel
independently of other components as
a bean:
<bean id="mymetamodel" class="org.eclipse.xtend.typesystem.xsd.XSDMetaModel"> <schemaFile value="metamodel.xsd" /> </bean> <component class="org.eclipse.xtend.typesystem.xsd.XMLReader"> <modelSlot value="model" /> <uri value="model.xml" /> <metaModel idRef="mymetamodel" /> </component>
Attention: It can lead to errors when XSDs are loaded multiple
times, which can only happen when using multiple
XSDMetaModels
within one workflow. The safe way
to go is to declare just one XSDMetaModel
per
workflow and reference it from all components that need it.
Properties:
schemaFile: optional, allowed multiple times: Specifies an XSD file which is being loaded. The path can be a complete URI, or relative to the project root or classpath.
registerPackagesGlobally: optional,
default "false": If true,
generated EPackages are registered to
org.eclipse.emf.ecore.EPackage.Registry.INSTANCE
,
EMF's global package registry. Warning: when running workflows from
your own java code, make sure to remove the generated packages from
the registry before the next run!
The XMLReader
reads one XML file which is
valid according to the XSDs loaded by the
XSDMetaModel
. The XML file is loaded as a model
and stored in the specified slot. Example:
<component class="org.eclipse.xtend.typesystem.xsd.XMLReader"> <modelSlot value="model" /> <uri value="model.xml" /> <metaModel idRef="mymetamodel" /> </component>
Properties:
slot: required: The name of the slot which in which the loaded model is stored. Other workflow components can access the model via referring to this slot.
uri: required: The file name of the XML file which should be read. Absolute URIs, and pathnames relative to the project root or to the classpath are valid.
metaModel: optional: Specifies the
XSDMetaModel
(see the section called “
XSDMetaModel
”) for the
XMLReader
. In case no
XSDMetaModel
is specified, an
XSDMetaModel
with default configuration is
instantiated implicitly. It is important to pay attention that all
needed XSDs can be found while the loading process: the section called “How to declare XML Schemas”.
useDocumentRoot: optional, default
"false": Dealing with XML files as models, most
people think of the XML's root element as the model's root object.
This is the default used by the XMLReader
.
But the XML's root element actually has a parent, the so-called
DocumentRoot. Additionally the DocumentRoot contains
comments/processing instructions and CDATA section which appears
before or after the XML's root element, and, most notably, the
DocumentRoot contains information about the used namespaces. If
useDocumentRoot is set to
true, the XMLReader
stores the DocumentRoot-Object instead the XML's root element's
object to the specified slot.
option: optional, can be specified
multiple times: Option specifies a key-value-pair, which is handed
on to the EMF's XMLResource in the loading process. Valid options
are documented via JavaDoc in interface
org.eclipse.emf.ecore.xmi.XMLResource
. Additionally, the XMLReader
supports these options:
DEFAULT_NAMESPACE: Specifies a default namespace, in case the XML file does not declare one:
<option key="DEFAULT_NAMESPACE" val="http://www.dlese.org/Metadata/opml" />
NAMESPACE_MAP: Specifies a mapping for namespaces, which is applied when loading XML files.
<option key="NAMESPACE_MAP"> <val class="org.eclipse.xtend.typesystem.xsd.lib.MapBean"> <mapping from="http://www.eclipse.org/modeling/xpand/example/model/wrong" to="http://www.eclipse.org/modeling/xpand/example/model/loadcurve" /> </val> </option>
The XMLWriter
writes the model stored in a
slot to an XML file. If the slot contains a collection of models, each
one is written to a separate file. The model(s) must have been
instantiated using an XSD-based meta model. Example:
<component class="org.eclipse.xtend.typesystem.xsd.XMLWriter"> <metaModel idRef="svgmm" /> <modelSlot value="svgmodel" /> <uri value="src-gen/mycurve.svg" /> </component>
Properties:
slot: required: The name of the slot which holds the model or the collection of models which shall be serialized to XML.
metaModel: required: The instance of
XSDMetaModel
, which holds the XSD that the
supplied models are based on. Also see the section called “
XSDMetaModel
”
uri: required if no uriExpression is specified: The file name of the XML file which should be written. Absolute URIs are valid. Use relative path names on your own risk.
uriExpression: required if no
uri is specified: In the scenario where
multiple XML files are written, this provides a mechanism to
determine the file name for each of them. The oAW-expression
specified in expression
is evaluated for each
file and has to return a file name. The model that is going to be
written is accessible in the expression via a variable that has the
name specified in varName
. Example:
<uriExpression varName="docroot" expression="'src-gen/'+ecore2xsd::getFileName(docroot)" />
option: optional, can be specified
multiple times: Option specifies a key-value-pair, which is handed
on to the EMF's XMLResource in the writing process. Valid options
are documented via JavaDoc in interface
org.eclipse.emf.ecore.xmi.XMLResource
.
The XMLBeautifier
uses EMF to load the XML
file, formats the mixed content (elements and text contained by the same
element) and writes the file back to disk applying a nice indentation
for the elements. The XMLBeautifier
is not
intended to be used in combination with the
XMLWriter
, since the
XMLWriter
cares about indentation by itself.
Instead, use it for "manually" constructed XML files using Xpand. Since
the frameworks for loading/storing XML always load the whole file into a
complex data structure in memory, this approach does not scale well for
huge XML files. Example:
<component class="org.eclipse.xpand2.Generator"> <metaModel idRef="mm" /> <expand value="${src-pkg}::${file}::Root FOR '${out}'" /> <outlet path="${src-gen-dir}" /> <beautifier class="org.eclipse.xtend.typesystem.xsd.XMLBeautifier"> <maxLineWidth value="60" /> <formatComments value="true" /> <fileExtensions value=".xml, .html" /> </beautifier> </component>
Properties:
maxLineWidth: optional: Specifies the number of character after which a linewrap should be performed.
formatComments: optional, default true: Specifies if formatting should also be applied to comments.
fileExtensions: optional, default ".xml, .xsl, .xsd, .wsdd, .wsdl": Specifies a filter for which files formatting should be applied. Only files that match one of the specified file extensions are processed.
loadOption: optional, can be specified
multiple times: Option specifies a key-value-pair, which is handed
on to the EMF's XMLResource in the loading process. Valid options
are documented via JavaDoc in interface
org.eclipse.emf.ecore.xmi.XMLResource
.
saveOption: optional, can be specified multiple times: Same as loadOption, except for the difference that these options are applied while the writing process. Example:
<saveOption key="XML_VERSION" val="1.1" /> <saveOption key="ENCODING" val="ASCII" />
In the code generation process an XML Schema is transformed to an
EMF Ecore model, which is then used as a meta model by EMF. XSD complex
data types are mapped to EClasses, XSD simple data types are mapped to EMF
data types defined in
org.eclipse.emf.ecore.xml.type.XMLTypePackage
and
org.eclipse.xtend.typesystem.xsd.XSDMetaModel
maps them to oAW
data types. The document XML
Schema to Ecore Mapping explains the mapping's details.
http://www.eclipse.org/modeling/emf/docs/overviews/XMLSchemaToEcoreMapping.pdf
There are three different ways to declare your XSDs. It does not matter which way you choose, or how you combine them, as long as the XSD Adapter can find all needed schemas.
Within the Workflow:
org.eclipse.xtend.typesystem.xsd.XSDMetaModel
can have any
amount of schemaFile
elements.
<component class="org.eclipse.xtend.typesystem.xsd.XMLReader"> <modelSlot value="model" /> <uri value="${file}" /> <metaModel id="mm" class="org.eclipse.xtend.typesystem.xsd.XSDMetaModel"> <schemaFile value="model/loadcurve.xsd" /> <schemaFile value="model/device.xsd" /> </metaModel> </component>
Within the XML file: XML files can contain
schemaLocation
attributes which associate the
schema's namespace with the schema's filename. If the schema is
created using WTP like described in the section called “Step 3: Create a Model using XML” , the
schemaLocation
attribute is created
automatically.
<?xml version="1.0" encoding="UTF-8"?> <device:Device xmlns:device="http://www.eclipse.org/modeling/xpand/example/model/device" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.eclipse.org/modeling/xpand/example/model/device device.xsd"> <device:Name>MyLaptop</device:Name> </device:Device>
Within an XSD: If one schema imports another, the
import
element can have a
schemaLocation
attribute, too.
<?xml version="1.0" encoding="UTF-8"?> <schema targetNamespace="http://www.eclipse.org/modeling/xpand/example/model/device" elementFormDefault="qualified" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:tns="http://www.eclipse.org/modeling/xpand/example/model/device" xmlns:lc="http://www.eclipse.org/modeling/xpand/example/model/loadcurve" xmlns:ecore="http://www.eclipse.org/emf/2002/Ecore"> <import namespace="http://www.eclipse.org/modeling/xpand/example/model/loadcurve" schemaLocation="loadcurve.xsd"> </import> <complexType name="Device"> <sequence> <element name="Name" type="string" /> <element name="LoadCurve" type="lc:LoadCurve" /> </sequence> </complexType> <element name="Device" type="tns:Device"></element> </schema>