Rename collection mapping field

[eduardoboucas]

When retrieving a composed view of document with multi-collection references, there needs to be information about what collection each of the documents is coming from. Currently, this is done using one field per Reference field, named as _ref[ReferenceFieldName] (e.g. authors leads to _refAuthors).

Example:

{
  "results": [
    {
      "_id": "560a5baf320039f1a1b68d4c",
      "_composed": {
        "crew": [
          "5ac16b70bd0d9b7724b24a41",
          "5ac16b70bd0d9b7724b24a42",
          "5ac16b70bd0d9b7724b24a43"
        ]
      },
      "_refCrew": {
        "5ac16b70bd0d9b7724b24a41": "writers",
        "5ac16b70bd0d9b7724b24a42": "directors",
        "5ac16b70bd0d9b7724b24a43": "producers"
      },
      "title": "Casablanca",
      "crew": [
        {
          "_id": "5ac16b70bd0d9b7724b24a41",
          "name": "Julius J. Epstein"
        },
        {
          "_id": "5ac16b70bd0d9b7724b24a42",
          "name": "Michael Curtiz"
        },
        {
          "_id": "5ac16b70bd0d9b7724b24a43",
          "name": "Hal B. Wallis"
        }
      ]
    }
  ]
}

In hindsight, the naming of this internal field was a poor design decision (my bad ✋). It forces clients to compute the name of the mapping field from the name of the Reference field, with the whole camel-case conversion to add more complexity to the mix.

Instead, a single field (e.g. _references) should hold all the collection mapping, in an object where keys are the Reference field names. The response above would be changed to:

{
  "results": [
    {
      "_id": "560a5baf320039f1a1b68d4c",
      "_composed": {
        "crew": [
          "5ac16b70bd0d9b7724b24a41",
          "5ac16b70bd0d9b7724b24a42",
          "5ac16b70bd0d9b7724b24a43"
        ]
      },
      "_references": {
        "crew": {
          "5ac16b70bd0d9b7724b24a41": "writers",
          "5ac16b70bd0d9b7724b24a42": "directors",
          "5ac16b70bd0d9b7724b24a43": "producers"
        }
      },
      "title": "Casablanca",
      "crew": [
        {
          "_id": "5ac16b70bd0d9b7724b24a41",
          "name": "Julius J. Epstein"
        },
        {
          "_id": "5ac16b70bd0d9b7724b24a42",
          "name": "Michael Curtiz"
        },
        {
          "_id": "5ac16b70bd0d9b7724b24a43",
          "name": "Hal B. Wallis"
        }
      ]
    }
  ]
}

This way, consumers don't need to compute any field names. Accessing the collection mapping for the crew fields is as simple as accessing the _references.crew object.