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default value for Boolean attribute and serialization [message #1763633]

Thu, 18 May 2017 04:31

Eclipse User

Hi all,

I have this metamodel

package myDsl : myDsl = 'http://www.xtext.org/example/mydsl/MyDsl'
{
	class Model
	{
		property greetings : Greeting[*|1] { ordered composes };
	}
	class Greeting
	{
		attribute name : String[?];
		attribute condition : Boolean[1] = 'true';
	}
}

It contains a boolean attribute "condition" (lowerbound 1, upperbound 1 and default value "true")
I create an Xtext project from this existing metamodel
The Xtext grammar is

// 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'
	'{'
		('greetings' '{' greetings+=Greeting ( "," greetings+=Greeting)* '}' )?
	'}';


Greeting returns Greeting:
	'Greeting'
	name=ID
	(condition?='valid')?
		;

I create the following model

Model {
	greetings {
		Greeting test valid
	}
}

I save and I open the model with the MyDsl editor model (the emf editor for mydsl).
I change the condition attribute value to "false".
When I save the model, i have this error

java.lang.RuntimeException: Could not serialize EObject via backtracking.
Constraint: Greeting_Greeting returns Greeting: (name=ID condition?='valid'?);
Values: name(1), condition(1)
Semantic Object: Model.greetings[0]->Greeting'ss'
URI: platform:/resource/mydsl/My.mydsl
Context: Greeting returns Greeting
	at org.eclipse.xtext.serializer.diagnostic.ISerializationDiagnostic$ExceptionThrowingAcceptor.accept(ISerializationDiagnostic.java:131)
	at org.eclipse.xtext.serializer.sequencer.BacktrackingSemanticSequencer.createSequence(BacktrackingSemanticSequencer.java:480)
	at org.xtext.example.mydsl.serializer.MyDslSemanticSequencer.sequence_Greeting(MyDslSemanticSequencer.java:53)
	at org.xtext.example.mydsl.serializer.MyDslSemanticSequencer.sequence(MyDslSemanticSequencer.java:35)
	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:412)
	at org.eclipse.xtext.serializer.sequencer.BacktrackingSemanticSequencer.createSequence(BacktrackingSemanticSequencer.java:478)
	at org.xtext.example.mydsl.serializer.MyDslSemanticSequencer.sequence_Model(MyDslSemanticSequencer.java:65)
	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.impl.Serializer.serialize(Serializer.java:118)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:142)
	at org.eclipse.xtext.serializer.impl.Serializer.serialize(Serializer.java:206)
	at org.eclipse.xtext.resource.XtextResource.doSave(XtextResource.java:369)
	at org.eclipse.emf.ecore.resource.impl.ResourceImpl.save(ResourceImpl.java:1430)
	at org.eclipse.emf.ecore.resource.impl.ResourceImpl.saveOnlyIfChangedWithMemoryBuffer(ResourceImpl.java:1144)
	at org.eclipse.emf.ecore.resource.impl.ResourceImpl.save(ResourceImpl.java:985)
	at myDsl.presentation.MyDslEditor$18.execute(MyDslEditor.java:1498)
	at org.eclipse.ui.actions.WorkspaceModifyOperation.lambda$0(WorkspaceModifyOperation.java:107)
	at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2240)
	at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2267)
	at org.eclipse.ui.actions.WorkspaceModifyOperation.run(WorkspaceModifyOperation.java:128)
	at org.eclipse.jface.operation.ModalContext$ModalContextThread.run(ModalContext.java:119)

It seems that it is caused by the default value.

Any suggestion how resolve it?

best regards,

[Updated on: Thu, 18 May 2017 04:33] by Moderator

Re: default value for Boolean attribute and serialization [message #1763635 is a reply to message #1763633]

Thu, 18 May 2017 05:18

Eclipse User

so you have an opposite default value that differs from the default value in the concrete syntax right?

you could play arround with the transient value service.

public class MyDslTransientValueService extends DefaultTransientValueService {

@Override
public boolean isTransient(EObject owner, EStructuralFeature feature, int index) {
if (feature == TestPackage.Literals.GREETING__FLAG) {
Boolean value = (Boolean)owner.eGet(feature);
if (value == null) {
return false;
} else if (value == Boolean.FALSE) {
return true;
}
}
return super.isTransient(owner, feature, index);
}

}

Re: default value for Boolean attribute and serialization [message #1763641 is a reply to message #1763635]

Thu, 18 May 2017 05:35

Eclipse User

Thanks Christian for the explanation. It works perfectly.

I share the complete solution

I created this class

package org.xtext.example.mydsl.services;

import org.eclipse.emf.ecore.EObject;
import org.eclipse.emf.ecore.EStructuralFeature;
import org.eclipse.xtext.parsetree.reconstr.impl.DefaultTransientValueService;

import myDsl.MyDslPackage;

public class MyDslTransientValueService extends DefaultTransientValueService {

	@Override
	public boolean isTransient(EObject owner, EStructuralFeature feature, int index) {
	if (feature == MyDslPackage.Literals.GREETING__CONDITION) {
	Boolean value = (Boolean)owner.eGet(feature);
	if (value == null) {
	return false;
	} else if (value == Boolean.FALSE) {
	return true;
	}
	}
	return super.isTransient(owner, feature, index);
	}
	
}

I updated my MyDslRuntimeModule class by adding this method

		override Class<? extends ITransientValueService> bindITransientValueService() {
			MyDslTransientValueService
	}

Re: default value for Boolean attribute and serialization [message #1763649 is a reply to message #1763641]

Thu, 18 May 2017 07:04

Eclipse User

Hi

It seems wrong to have to play around with such internals to make a model work.

Presumably you specified true as the default in order to give a statistical saving on the XMI size since true is much more common than false. Otherwise there is no point.

But if that is a saving for your XMI surely it is also true in your DSL, so why are DSL and XMI inconsistent?

I suggest that you change the XMI default to 'false' and the artificial problem goes away and a fancy hack is unnecessary.

Regards

Ed Willink

Re: default value for Boolean attribute and serialization [message #1763650 is a reply to message #1763649]

Thu, 18 May 2017 07:15

Eclipse User

Ed Willink wrote on Thu, 18 May 2017 13:04

Hi
I suggest that you change the XMI default to 'false' and the artificial problem goes away and a fancy hack is unnecessary.

Where can I change it? in the mydsl.genmodel?

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