Reject nonunique resources

[20joshuaz]

Issue: #33

About me

This PR adds logic to check that, per jsonapi's spec, a single canonical resource object is returned with each response. It checks resource objects across the primary data and included sections to find duplicates (duplicate being resources objects with the same type & id). It also checks every relationship section for duplicates.

The following documents were previously accepted but now rejected:

Duplicate resource objects in primary data

{
  "data": [
    {
      "id": "1",
      "type": "articles",
      "attributes": {
        "title": "A"
      }
    },
    {
      "id": "1",
      "type": "articles",
      "attributes": {
        "title": "B"
      }
    }
  ]
}

Duplicate resource objects in included section

{
  "data": {
      "id": "1",
      "type": "articles",
      "attributes": {
        "title": "A"
      },
      "relationships": {
        "comments": {
          "data": { "type": "comments", "id": "1" }
        }
      }
    },
  "included": [{
    "type": "comments",
    "id": "1",
    "attributes": {
      "body": "I like XML better"
    }
  }, {
    "type": "comments",
    "id": "1",
    "attributes": {
      "body": "I like YAML better"
    }
  }]
}

Duplicate resource objects across primary data and included

{
  "data": [{
      "id": "1",
      "type": "employees",
      "attributes": {
        "name": "John Doe"
      },
      "relationships": {
        "managers": {
          "data": { "type": "employees", "id": "2" }
        }
      }
    }, {
      "id": "2",
      "type": "employees",
      "attributes": {
        "name": "Mary Jane"
      },
      "relationships": {
        "managers": {
          "data": { "type": "employees", "id": "3" }
        }
      }
    }],
  "included": [{
    "type": "employees",
    "id": "2",
    "attributes": {
      "name": "Mary Jane"
    }
  }]
}

Duplicate resource linkages

{
  "data": {
      "id": "1",
      "type": "articles",
      "attributes": {
        "title": "A"
      },
      "relationships": {
        "comments": {
          "data": [{ "type": "comments", "id": "1" }, { "type": "comments", "id": "1"}]
        }
      }
   }
}

Testing

Added tests that cause error to be thrown

Questions

• The jsonapi spec specifically calls out resource objects to be unique, but it doesn't mention resource linkages (the last example in the About me section). Is checking for duplicate resource linkages in every relationship section overkill?