Modelling a resource hierarchy that is not consistent

1

I have a resource model that, as it travels down the related resource hierarchy, becomes potentially inconsistent and am looking for a decent way to model it in a standard way.

Say I have a nested resource: items within a product. Items and Products have unique type and IDs. Simple so far.

Then I have a second concept which extends some behaviour or rules around the items, in this case grouping them together so that when a Quote is built, only one item from a group may be chosen.

Conceptually this would look like:

Product
 - item A1
 - item B1
 - grouping C (one of)
    - item C1 
    - item C2

This grouping is what I am trying to figure out how to model to fit the spirit of the json-api spec.

My attempt

I promote the “grouping” concept to a resource that can be linked as a relationship:

{
  "data" : { "type": "products", "id": 1, },
  "relationships": {
    "items": { 
      "links": { 
        "self": "http://example.com/products/1/relationships/items" 
        "related": "http://example.com/products/1/items" 
      }
      "data": { "type": "items": "id": 100 } }
  }
}
----
{
  "data" : { "type": "items", "id": 100 },
  "relationships": {
    "grouping": { 
      "links": {
        "self": "http://example.com/products/1/items/relationships/grouping",
        "related": "http://example.com/products/1/grouping/22"
      }
      "data": { "type": "grouping": "id": 22 } 
    },
  }
}

{
  "data" : { "type": "grouping", "id": 22 },
  "relationships": {
    "items": { ... }
}

This seems to work in the sense that the items and groupings can be specified, created, updated and identified individually.

My problem here is that grouping only has context within a product. There is no http://example.com/grouping/22 endpoint, it only exists within product/1.

That seems to be OK after I read 367 and others. It seems as though the suggestion was to define grouping as type product_grouping and then build a composite key that is unique to the product+grouping combo. This is fine, grouping is unique to a product.

This has me thinking on how to handle the resource linkage…

If I define “grouping” as existing within product then it can only be reached as

  • http://example.com/product/1/grouping/22
  • with { “data”: { “type”: “product_grouping”, “id”: <hash of 1_22> } }

Is this assumption correct? There would be no http://example.com/grouping/22 ?
Can I safely assume that resource linkage doesn’t imply that a URL can be built from type and ID, only that it can be looked up in a compound document?

My other problems here is that the poor client has to figure out this hierarchy by itself so perhaps one could add a groupings relationship to the product itself.

I hope this is clear. It has been quite hard for me to describe exactly what I am struggling with conceptually as there a few concepts at play here.