Repo API: Represent dangling pointers

[enikao]

We represent links (i.e. both children and references) by their id.
How do we handle the case that the node with this id is not logically contained in the result set (because it's out of scope of the query)?

Aspects

• Distinguish invalid link targets from not loaded ones
• Know the type of the target node (might be useful for e.g. EMF-based implementation)

Possible representations

Just target id

Example:

{
  "containsProxies": true
  "nodes": [
    {
      "id": "a",
      "type": "PetOwner",
      "references": {
        "myPet": "x" // no node with id "x" present
      }
    }
  ]
}

• Less data
• Cannot distinguish between invalid id and unresolved id
• Server could send back a flag whether data contained any proxies

Proxy for target

Example:

{
  "nodes": [
    {
      "id": "a",
      "type": "PetOwner",
      "references": {
        "myPet": "x"
      }
    },
    {
      "id": "x",
      "type": "Dog",
      "state": "[full | proxy | invalid]"
    }
  ]
}

• After just reading the list of nodes, we know whether we have an unresolved reference
• We can easily know reference target type
• Can differentiate between invalid id and unresolved id
• If querying closure and result contains invalid id, client can identify them

=> Decision: For now, don’t store proxies in node list. Might be changed in the future (compatible, additive API change).

[joswarmer]

The reference target type is defined in the metamodel, therefore we always know the reference target type. Assuming we know the metamodel. Is there a reason why it would not be defined when using the target Id?

[joswarmer]

Since a pointer can always become dangling, when the target is deleted, I think we need something (like e.g. a name) next to the target id, so we can rebind the target using a scoping component.
Not all target references may have names, so this will only work a limited (but important) subset.

[enikao]

The reference target type is defined in the metamodel, therefore we always know the reference target type. Assuming we know the metamodel. Is there a reason why it would not be defined when using the target Id?

The target might be of a different type, e.g. if I changed the metamodel and didn't update my reference.

[enikao]

Since a pointer can always become dangling, when the target is deleted, I think we need something (like e.g. a name) next to the target id, so we can rebind the target using a scoping component. Not all target references may have names, so this will only work a limited (but important) subset.

We do (resolveInfo), see #36

[enikao]

@joswarmer are your questions answered? Then I'd close.

[joswarmer]

Ok