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manage eopposite references coming from imported metamodel [message #1765199]

Wed, 07 June 2017 13:13

Fy Za

Messages: 245
Registered: March 2010

Senior Member

Hi everybody,

I have this metamodel
index.php/fa/29579/0/

I create a Xtext grammar from this metamodel

// automatically generated by Xtext
grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.common.Terminals

import "http://www.xtext.org/example/mydsl/MyDsl" 
import "http://www.eclipse.org/emf/2002/Ecore" as ecore

Model returns Model:
	{Model}
	'Model'
	name=ID
	'{'
		('classAs' '{' classAs+=ClassA ( "," classAs+=ClassA)* '}' )?
	'}';
	
ClassA returns ClassA:
	{ClassA}
	'ClassA'
	name=ID
	'{'
	//	('referingbs' '(' referingbs+=[ClassB|ID] ( "," referingbs+=[ClassB|ID])* ')' )?
		('classb' '{' classb+=ClassB ( "," classb+=ClassB)* '}' )?
	'}';

ClassB returns ClassB:
	'ClassB'
	name=ID
	'{'
		'target' target=[ClassA|ID]
	'}';

My models are saved as XMI using a mechanism described in previous posts (That is not the issue).

The problem comes from the "referingbs" reference which is an eopposite reference to "target" reference.

When I create a model containing an instance of ClassB that refers to ClassA instance via target reference,
Xtext throws an error

java.lang.RuntimeException: Could not serialize ClassA:
ClassA.referingbs violates the upper bound: It holds 1 values, but only 0 are allowed.
Semantic Object: Model'model1'.classAs[0]->ClassA'class1'
URI: temp.my
Context: ClassA returns ClassA
	at org.eclipse.xtext.serializer.diagnostic.ISerializationDiagnostic$ExceptionThrowingAcceptor.accept(ISerializationDiagnostic.java:131)
	at org.eclipse.xtext.serializer.sequencer.BacktrackingSemanticSequencer.createSequence(BacktrackingSemanticSequencer.java:503)
	at org.xtext.example.mydsl.serializer.MyDslSemanticSequencer.sequence_ClassA(MyDslSemanticSequencer.java:59)
	at org.xtext.example.mydsl.serializer.MyDslSemanticSequencer.sequence(MyDslSemanticSequencer.java:38)
	at org.eclipse.xtext.serializer.sequencer.AbstractSemanticSequencer.createSequence(AbstractSemanticSequencer.java:67)
	at org.eclipse.xtext.serializer.acceptor.SequenceFeeder.acceptEObjectRuleCall(SequenceFeeder.java:325)
	at org.eclipse.xtext.serializer.acceptor.SequenceFeeder.acceptRuleCall(SequenceFeeder.java:352)
	at org.eclipse.xtext.serializer.acceptor.SequenceFeeder.accept(SequenceFeeder.java:263)
	at org.eclipse.xtext.serializer.sequencer.BacktrackingSemanticSequencer.accept(BacktrackingSemanticSequencer.java:434)
	at org.eclipse.xtext.serializer.sequencer.BacktrackingSemanticSequencer.createSequence(BacktrackingSemanticSequencer.java:501)
	at org.xtext.example.mydsl.serializer.MyDslSemanticSequencer.sequence_Model(MyDslSemanticSequencer.java:92)
	at org.xtext.example.mydsl.serializer.MyDslSemanticSequencer.sequence(MyDslSemanticSequencer.java:44)
	at org.eclipse.xtext.serializer.sequencer.AbstractSemanticSequencer.createSequence(AbstractSemanticSequencer.java:67)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:115)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:128)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:192)
	at org.eclipse.xtext.resource.XtextResource.doSave(XtextResource.java:386)
	at org.eclipse.emf.ecore.resource.impl.ResourceImpl.save(ResourceImpl.java:1430)

I found this message https://www.eclipse.org/forums/index.php?t=msg&th=1079030&goto=1737136&#msg_1737136
that proposes to customize ITransientValueService feature.

I customize it by adding the following

class MyDslRuntimeModule extends AbstractMyDslRuntimeModule {
	
	def Class<? extends LegacyTransientValueService> bindITransientValueService2() {
		MyDslTransientValueService
	}
}

public class MyDslTransientValueService extends LegacyTransientValueService {
	@Override
	public ValueTransient isValueTransient(EObject semanticObject, EStructuralFeature feature) {
		if (feature == MyDslPackage.Literals.CLASS_A__REFERINGBS) {
			return ValueTransient.YES;
		}
		return super.isValueTransient(semanticObject, feature);
	}

}

However the original error always appears (ClassA.referingbs violates the upper bound: It holds 1 values, but only 0 are allowed).

My question: how can I resolve this eopposite issue in Xtext?

I share the complete case-study containing an example (in the org.eclipse.example.mydsl.example project)
if someone is interested to reproduce.

best regards

Attachment: MyDsl.jpg
(Size: 35.69KB, Downloaded 479 times)
Attachment: xtext-eopposite.zip
(Size: 1.78MB, Downloaded 89 times)

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