Relationship Data - missing or by design?

[mattgi]

Should I always see relationship data, regardless of link config or include query?

By this, I mean /items currently produces:

{
    "data": [
        {
            "type": "items",
            "id": "item-de4e78d3-b2ec-48dd-8dd7-6088881a2bfe",
            "attributes": {
                "type": 0,
                "title": "New York",
                "cover": null,
                "slug": null,
                "version": 1
            },
            "relationships": {
                "owner": {
                    "links": {
                        "self": "/items/item-de4e78d3-b2ec-48dd-8dd7-6088881a2bfe/relationships/owner",
                        "related": "/items/item-de4e78d3-b2ec-48dd-8dd7-6088881a2bfe/owner"
                    },
                "createdBy": {},
                "updatedBy": {},
                "deletedBy": {}
                }
            }
        }
    ]
}

If I include owner (/items?include=owner):

{
    "data": [
        {
            "type": "items",
            "id": "item-de4e78d3-b2ec-48dd-8dd7-6088881a2bfe",
            "attributes": {
                "type": 0,
                "title": "New York",
                "cover": null,
                "slug": null,
                "version": 1
            },
            "relationships": {
                "owner": {
                    "links": {
                        "self": "/items/item-de4e78d3-b2ec-48dd-8dd7-6088881a2bfe/relationships/owner",
                        "related": "/items/item-de4e78d3-b2ec-48dd-8dd7-6088881a2bfe/owner"
                    },
                    "data": {
                        "type": "users",
                        "id": "user-b607e7dc-3a9d-4360-8495-dd37c4c99de8"
                    }
                },
                "createdBy": {},
                "updatedBy": {},
                "deletedBy": {}
            }
        }
    ],
    "included": [
        {
            "type": "users",
            "id": "user-b607e7dc-3a9d-4360-8495-dd37c4c99de8",
            "attributes": {
                "email": "poo@shorthand.com",
                "firstName": "Matthew",
                "lastName": "Gint2y",
                "slug": "slugger",
                "version": 1
            },
            "relationships": {
                "createdBy": {},
                "updatedBy": {},
                "deletedBy": {}
            }
        }
    ]
}

Even when I am not asking for includes (or if links are turned off), I was expecting the relationships to always have data:

"relationships": {
                "owner": {
                    "data": {
                        "type": "users",
                        "id": "user-b607e7dc-3a9d-4360-8495-dd37c4c99de8"
                    }
                },

Is this expected behavior or am I potentially missing something on my model?

      [HasOne("owner")]
      public virtual User Owner { get; set; }

      public string OwnerId { get; set; }

Based on http://jsonapi.org/format/#document-resource-objects and their { article } snippet, it suggests data should be there.. I must be missing something somewhere?

[jaredcnance]

I think this is an oversight. In the case of a dependent HasOne relationship we can include this easily and I think maybe we should. However, on the independent side of a HasOne (in the case of a 1:(0-1) relationship) we will not include this because it would necessitate a SQL JOIN and would be unexpected behavior.

[jaredcnance]

I think we need to do some setup when we build the ContextGraph so we don't do any extra request-time reflection. That would involve modifying the ContextGraphBuilder to set some HasOneAttribute.IsDependent and maybe even a reference to the RelationshipId PropertyInfo. Then the DocumentBuilder will need to pull out the value. With tests, I would expect it to take me a couple hours. I'd also be happy to work with you if you want to take a stab at it.

[mattgi]

Ha, I just deleted my comment.

I was going to just try messing with the DocumentBuilder

Will start to get me used to the code if nothing else.

[mattgi]

A very quick hack was to:

1. copy the source DocumentBuilder into my local codebase,
2. Inject the copy in startup via services.AddScoped<IDocumentBuilder, JsonBuilder>();
3. Make this hack to AddRelationships:

private void AddRelationships(DocumentData data, ContextEntity contextEntity, IIdentifiable entity) {
...
  if (RelationshipIsIncluded(r.PublicRelationshipName)) {
...
  } else {
    relationshipData.SingleData = GetSimpleRelationship(entity, r.InternalRelationshipName);
  }
...

4. Add the corresponding method:

    private Dictionary<string, string> GetSimpleRelationship(object entity, string name) {
      var entityType = entity.GetType();
      var contextEntity = _contextGraph.GetContextEntity(entityType);
      var property = contextEntity.Relationships.First(f => f.InternalRelationshipName == name);
      if (property == null) {
        return null;
      }

      var propertyInfo = entityType.GetProperty(string.Concat(name, "Id"));
      if (propertyInfo == null) {
        return null;
      }

      var id = (string) (propertyInfo.GetValue(entity, null));
      if (id == null) {
        return null;
      }

      return new Dictionary<string, string> {
        {
          "type",
          property.Type.Name
        },
        { "id", id }
      };
    }

---

It assumes that when you have a relationship named Something on the entity that there will be a prop named SomethingId that stores the PK for that related entity (and that it's a string).

Very hacky, and I probably need to consider more complex models if I run in to them, but it quickly unblocked the clientside dev.

FWIW, I started to go down the rabbit hole of ContextGraph changes but quickly came back up for air before I sunk a day on it. :)

Thanks for pointing me in the right direction for now.

[crfloyd]

I currently have the need to include "data" (without attributes) for each relationship by default. From what I could tell, the only thing preventing this is the check in DocumentBuilder.cs in the AddRelationships() method:
if (RelationshipIsIncluded(r.PublicRelationshipName))
removing this check just includes the data for the relationship by default. I am using a document database and not the default EntityFramework style so I do not know if there are any implications to doing this outside my use-case. It would be nice to have the ability to at least configure the framework to allow for the default inclusion of data for resources.

[jaredcnance]

The only challenge I see is this requirement from the spec (let me know if I'm just missing something here):

If an endpoint supports the include parameter and a client supplies it, the server MUST NOT include unrequested resource objects in the included section of the compound document.

Without that check, I think there are conditions under which we would no longer comply with the specification. As a framework we have a strict constraint of complying with the spec by default. However, I 100% believe we should make it simple for applications to deviate as needed.

A possible option is to make RelationshipIsIncluded protected so you can simply protected override bool RelationshipIsIncluded(string relationshipName) => true; but I'm not sure that's the best solution.

[crfloyd]

But isn't that referring to the "included" section of the document response? This is different from the inclusion of the "data" field in the "relationships" section. Below is an example response showing a response with included data. This response returns the included information requested in the "included" section but still includes the "data" at the relationship level. This would always be present regardless of what included information was requested.

[jaredcnance]

Ah, yes sorry my mistake. You’re correct.