| Not representable well-behaving feature [message #1244123] |
Tue, 11 February 2014 23:39  |
 Emre T
Messages: 119
Registered: April 2013 |
Senior Member |
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Hello
in the definition of my @QueryBasedFeature patterns, I am getting the following warning for derived references of my own model elements to other elements of an other imported Ecore package:
The derived/volatile feature referenceConstruct of class CreateInterface used in the path expression is not representable in EMF-IncQuery. For details, consult the documentation on well-behaving features.
I have double-checked, that these references are derived (true), volatile (true), transient (true) and non-changeable (false), so well-behaving. I couldn't actually got my queries run, because of some other errors, but I wanted to know, whether you are familiar with these warnings are?
Thanks a lot!
Emre
P.S: The references are also non-containment references from my model classes to other imported model classes and have different cardinailities, if it is any important.
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| Re: Not representable well-behaving feature [message #1244350 is a reply to message #1244123] |
Wed, 12 February 2014 07:47  |
Gabor Bergmann
Messages: 36
Registered: July 2009 |
Member |
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I think you misunderstand what we mean by well-behaving derived feature.
Please take a look at: https://wiki.eclipse.org/EMFIncQuery/UserDocumentation/Query_Based_Features#Well-behaving_structural_features
The key is that whenever the value of the derived feature changes, it must be able to emit proper EMF notifications - otherwise live queries / incremental evaluation would not be possible. For example, something like java.lang.System.currentTimeMillis(), if it were an EMF structural feature, would be transient, volatile, derived, and non-changeable. Yet it would not be well-behaving, as its return value could (and would) change between invocations, without providing notifications whenever a millisecond has passed.
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| Re: Not representable well-behaving feature [message #1245225 is a reply to message #1245212] |
Thu, 13 February 2014 13:38 |
Abel Hegedus
Messages: 197
Registered: September 2015 |
Senior Member |
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Actually, "derived, volatile, transient and non-changeable" means that they are _not well-behaving_ since by default, EMF will not provide change notifications for such features.
If you use derived features (non query-based) and manually code them to send notifications (e.g. ADD, SET, REMOVE), then your feature is _made_ well-behaving, and you can tell EMF-IncQuery this fact by registering it through an extension.
However, if you use _query-based_ derived features (by defining a pattern and adding the @QueryBasedFeature annotation), those will be well-behaving by definition, since the query-based feature runtime plugin will make sure that correct notifications are sent. Therefore, the well-behaving extension is automatically generated along with the modification of the getter code.
The extension is added to the plugin.xml of the EMF-IncQuery project where you defined the pattern. If you include this project in the runtime Eclipse, then those generated extensions will be parsed and the EMF-IncQuery editor will also know that the feature is well-behaving.
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