Question

I know there is a simple solution for this but I have no idea how to implement it.

I’m looking for how to implement the answer rather than what I need to do. Half the answer is already on this page:
Xtext cross referencing and scoping

My problem is with the grammar below:

DomainModel:
    "DOMAINMODEL" name=ID "{"
        "ENTITYS" "{"
            (Entitys+=Entity)*
        "}"
        "ENTITY_RELATIONSHIP" "{"
            (Relationships+=Relationship)*
        "}" 
    "}";

Entity:
    name=ID "{"
        (Attributes+=Attribute)*
    "}";

Attribute:
    StringAttribute | NumberAttribute | ImageAttribute;

StringAttribute:
    "STRING" name=ID;

NumberAttribute:
    "NUMBER" name=ID;

ImageAttribute:
    "IMAGE" name=ID;

// Relationship = [new table name] : [shared key name] -> ref_table(ref_id)
Relationship:
    name=ID ":" newEntityName=ID "->" refEntityName=[Entity|ID]"("refName=[Attribute|ID]")"; // <- Problem here

When I write the model, I cannot get the “refName=[Attribute|ID]” to reference to attributes inside an entity.
In the code below

DOMAINMODEL auctionHouse{
    ENTITYS {

       lots{      
          NUMBER id0
          NUMBER lotNo
          STRING name
          STRING priceEstimate
          STRING description
       }  
       auctions{
          NUMBER id1
          NUMBER date
          STRING description
       }
       auction_lots{
          NUMBER id2
          STRING lot_id
          NUMBER auction_id
       }

    }

    ENTITY_RELATIONSHIP {
        auction_lots : lot_id -> lots(id0) // <- Will not find 'id0'
        auction_lots : auction_id -> auctions(id1) // <- Will not find 'id1'
    }

}

How can I widen the scope?
How can I differentiate between two attributes with the same name but in different scopes?

Answer 1

The problem with the references is that they simply cannot be found in that scope, what you could do is introduce a qualified name and use that in your cross-reference and change your grammar accordingly, ie:-

QualifiedName:
    ID ('.' ID)*;

Relationship:
    name=ID ":" newEntityName=ID "->" refName=[Attribute|QualifiedName];

Now it should be possible to reference by using the qualified ID:

ENTITY_RELATIONSHIP {
    auction_lots : lot_id -> auctionHouse.lots.id0
    auction_lots : auction_id -> auctionHouse.auctions.id1
}

If you can’t change the grammar like this to make use of the default way Xtext handles names then you would need to look into providing your own qualified names, a great article for that is this Qualified Names Article