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Referencing existing metamodels in a DSL [message #688051]

Thu, 23 June 2011 19:08

Zoltan Ujhelyi

Messages: 392
Registered: July 2015

Senior Member

We are currently experimenting with Xtext, and would like to create a special constraint language over EMF models.

The Xtext grammar language contains similar option: metamodels (EPackages) can be referenced via their namespace URIs, and then EClassifiers can be used inside the language.

I would like to create a similar functionality for our constraint language. I defined our import option similarly to the one in xtext.xtext:

Import:	'import' ePackage=[ecore::EPackage|STRING] ('as' alias=ID)?;

, and used the code from the Xtext scope provider to gather the list of NS URIs (and thus content assist was also working) with a minor modification: the qualified name is created using the default qualified name converter:

	public IScope scope_EPackage(Import ctx, EReference ref){
		IScope current = new SimpleScope(IScope.NULLSCOPE, Iterables.transform(EPackage.Registry.INSTANCE.keySet(), new Function<String, IEObjectDescription>() {
			public IEObjectDescription apply(String from) {
				InternalEObject proxyPackage = (InternalEObject) EcoreFactory.eINSTANCE.createEPackage();
				proxyPackage.eSetProxyURI(URI.createURI(from));
				
				return EObjectDescription.create(qualifiedNameConverter.toQualifiedName(from), proxyPackage, Collections.singletonMap("nsURI", "true"));
			}
		}));
		return current;
	}

However, the inserted namespace is not resolved: I got a nullpointer exception, as during the linking phase it tried to resolve the object of the URI "http://www.eclipse.org/emf/2002/Ecore", but its fragment part was missing.

My question is, what might be missing from my code? Do I have to register some specific linking functionality? Or should I use a completely different mechanism for resolution?

Thank you for your help,
Zoltán Ujhelyi

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