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Serializing Instances based on the Domainmodel (15 minutes tutorial) [message #1806740]

Tue, 14 May 2019 10:39

Eclipse User

Hi,
I want to programmatically create EMF instances based on the Domainmodel / Entity DSL out of the 15 minutes tutorial (https://www.eclipse.org/Xtext/documentation/102_domainmodelwalkthrough.html#write-the-grammar) and serialize them back into their textual Xtext representation.

E.g., I want to create an EMF instances according to this Xtext representation:

datatype String
 entity Blog {
title: String
 }

My solution is as follows:

@Inject Serializer serializer

  def void serializer() {
    val f = DomainmodelFactory.eINSTANCE
    
    val domainModel = f.createDomainmodel
    val dataType = f.createDataType
    dataType.setName("String")
    domainModel.getElements.add(dataType)
    
    val entity = f.createEntity
    entity.setName("Blog")
    domainModel.getElements.add(entity)
    
    val feature = f.createFeature
    feature.setName("title")
    feature.setType(dataType)
    entity.getFeatures.add(feature)

    println(serializer.serialize(domainModel))
  }

Unfortunately, I get a NullPointerException. It seems to me as if the cross references in square brackets are the problem, because without them everything works just fine. Does anyone have a solution for this problem / know whats wrong?:

java.lang.NullPointerException
	at org.eclipse.xtext.scoping.impl.ImportedNamespaceAwareLocalScopeProvider.getResourceScope(ImportedNamespaceAwareLocalScopeProvider.java:103)
	at org.eclipse.xtext.scoping.impl.ImportedNamespaceAwareLocalScopeProvider.getScope(ImportedNamespaceAwareLocalScopeProvider.java:97)

Re: Serializing Instances based on the Domainmodel (15 minutes tutorial) [message #1806748 is a reply to message #1806740]

Tue, 14 May 2019 12:15

Eclipse User

You should create a new resourceset and resource and add the model to the resource
Does it work then?

Re: Serializing Instances based on the Domainmodel (15 minutes tutorial) [message #1806752 is a reply to message #1806748]

Tue, 14 May 2019 13:12

Eclipse User

It works. Thanks! I stumbled across the same issue on Stackoverflow and would also post the solution code there, if that's okay..

About justification why the ResourceSet is needed: Do I get it right that the serialization method needs access to all elements to map the cross references and that this is made possible by attaching the model to the ResourceSet (e.g. it provides the method getAllContents())?

Here's the solution:

    @Inject Serializer serializer
	
//new
    @Inject
    ResourceSet resourceSet

 def void serializer() {
  	
//new
    val resource = resourceSet.createResource(URI.createURI("dummy/test.dmodel"))
    
    val f = DomainmodelFactory.eINSTANCE
    
    val domainModel = f.createDomainmodel
    val dataType = f.createDataType
    dataType.setName("String")
    domainModel.getElements.add(dataType)
    
    val entity = f.createEntity
    entity.setName("Blog")
    domainModel.getElements.add(entity)
    
    val feature = f.createFeature
    feature.setName("title")
    feature.setType(dataType)
    entity.getFeatures.add(feature)
    
     //new
    resource.getContents.add(domainModel)

    println(serializer.serialize(domainModel))

  }

Re: Serializing Instances based on the Domainmodel (15 minutes tutorial) [message #1806754 is a reply to message #1806752]

Tue, 14 May 2019 13:44

Eclipse User

yes and no. the resourceset specifies the "space" / container where objects for references are searched.
btw you should use

@Inject
Provider<ResourceSet> rsp

and rsp.get to obtain the rs
(if you want to follow the ususal pattern)

Re: Serializing Instances based on the Domainmodel (15 minutes tutorial) [message #1806759 is a reply to message #1806754]

Tue, 14 May 2019 14:58

Eclipse User

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