Using $ref in definition objects

[StreakyCobra]

Hi,

I’m currently experimenting with the data contract specification and its associated CLI. During my tests, I noticed that using $ref in definition objects is not working. I assume this is expected, as the specification does not list $ref as a field of "Definition" objects.

Adding support for this use case would simplify working with complex data models: the use of $ref in definition objects would significantly improve composability and reduce repetition in models and definitions.

An example is provided below for reference.

Here are a few questions to start the discussion:

• Is it correct that using $ref in definitions is not supported at the moment?
• Is there a technical limitation preventing this use case?
• Is this a direction the project would like to explore, and would it be difficult to implement?

Looking forward to answers and discussion.

Cheers,
Fabien

---

dataContractSpecification: 1.1.0
id: my-data-contract-id
info:
  title: My Data Contract
  version: 0.0.1
  description: My Data Contract

models:
  my_data_model:
    description: My Data Model
    type: object
    fields:
      pair:
        $ref: "#/definitions/pair"

definitions:
  pair:
    description: A pair of IDs
    type: object
    fields:
      first:
        $ref: "#/definitions/id"
      second:
        $ref: "#/definitions/id"
  id:
    description: An ID
    type: string

Trying to export this data contract as AVRO or Protobuf results in an erroneous schema.

Avro:

• datacontract-cli version: 0.10.14
• Comand: datacontract export --format avro minimal.yaml

The ID fields are of type ["null", "null"] instead of ["null", "string"]:

{
  "type": "record",
  "name": "my_data_model",
  "doc": "My Data Model",
  "fields": [
    {
      "name": "pair",
      "doc": "A pair of IDs",
      "type": [
        "null",
        {
          "type": "record",
          "name": "pair",
          "doc": "A pair of IDs",
          "fields": [
            {
              "name": "first",
              "type": [
                "null",
                "null"
              ]
            },
            {
              "name": "second",
              "type": [
                "null",
                "null"
              ]
            }
          ]
        }
      ]
    }
  ]
}

Protobuf:

• datacontract-cli version: 0.10.14
• Comand: datacontract export --format protobuf minimal.yaml

The ID fields are of type None instead of string:

syntax = "proto3";

/* My Data Model */
message My_data_model {
    /* A pair of IDs */
  message Pair {
    optional None first = 1;
    optional None second = 2;
  }
  /* A pair of IDs */
  optional Pair pair = 1;
}