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Custom validation of constraints from existing metamodel [message #1776346]

Wed, 15 November 2017 14:03

Matteo M.

Messages: 40
Registered: May 2012

Member

Hello,
I have a legacy Ecore metamodel that I cannot modify where a EClass "Foo" has an attribute "bar" with multiplicity 1 -- i.e., it is a required attribute. The EMF tree model editor I have generates a default value for "bar", which is generally ok, except when the user must use specific (custom) logics to derive a value for it. In that case the user will overwrite the generated default to insert the desired value.

Now, I want to define a grammar for this Ecore metamodel, and I want to emulate the behavior of the model editor above.

In other words, I want the xtext editor does not force the user to insert a value for "bar" each time, and that some Java code is called behind the scenes when "bar" is not specified to comply with the multiplity-1 constraint.

In yet other words, I want the editor does not raise any error when the user does:

Foo fobj;

because some Java code will be called behind the scenes to properly fill the "bar" attribute with some defaults.
On the other hand, this one of course is also valid:

Foo fobj with bar abc123;

Any hints on how do I do it?

Thanks.
Best,
--
Matteo

[Updated on: Wed, 15 November 2017 14:07]

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Re: Custom validation of constraints from existing metamodel [message #1776347 is a reply to message #1776346]

Wed, 15 November 2017 14:07

Christian Dietrich

Messages: 14496
Registered: July 2009

Senior Member

I'd have a look at org.eclipse.xtext.parser.DefaultEcoreElementFactory.create(EClassifier)
maybe you can set the default value after creation

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Re: Custom validation of constraints from existing metamodel [message #1776350 is a reply to message #1776347]

Wed, 15 November 2017 14:27

Matteo M.

Messages: 40
Registered: May 2012

Member

Hi Christian, thanks for the immediate reply!
I've just looked around (e.g., here: http://download.eclipse.org/modeling/tmf/xtext/javadoc/2.3/org/eclipse/xtext/parser/DefaultEcoreElementFactory.html#create(org.eclipse.emf.ecore.EClassifier)). Can you elaborate just a bit how am I supposed to "customize" the call to method "create" or force a call to method "set" (which "Assigns a given value to a feature of the element _this.")?

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