External ID uniqueness

[cmgrulke]

As a researcher I want external ids to be unique within a list So that they can actually be guaranteed to be clear identifiers back to an external source

Acceptance Criteria:

• On update or creation of a record (issue #175), ensure that the list_id, external_id pair is unique.
• if not unique, return an error with message "External IDs must be unique within a list. The External ID submitted is already associated with ${rid}"
• the error response body contains a link to the conflicting record resource

Test:

[mwfrost]

Proposed test requests

With the fixtures loaded, there will be a Record object with external_id of 47 and list id of 2.

This POST will attempt to create another Record with those same values:

{
"data": {
        "type": "record",
        "attributes": {
            "external_id": "47",
            "score": 4.7,
            "message": "I made a record",
            "is_validated": false
        },
        "relationships": {
            "list": {
                "data": {
                "id": 2,
                "type": "list"
                }
            },
            "substance": {
                "data": {
                "id": 2,
                "type": "substance"
                }
            }
        }
    }
}

When it fails, change the external_id and try again. It will succeed. Then change the id for the "list" relationship to "1" and it should succeed again.