JSON Schema: array where non-null elements are unique

Question

I am trying to construct a JSON schema that meets the following:

1. Declares a top-level object with at least one property
2. The value of each property will be an array, each of which must contain exactly N items
3. Array items must be integers taken from the closed interval [J, K] , or null
4. Integer items in each array must be unique within that array
5. There is no uniqueness constraint applied to null (so no implied relationship between N and the interval size KJ )

The problem I am running into is #4 and #5. It is easy enough to meet the first 3 requirements, plus part of the 4th, using this schema:

{
  "$schema": "http://json-schema.org/draft/2019-09/schema#",
  "type": "object",
  "minProperties": 1,
  "additionalProperties": {
    "type": "array",
    "minItems": N,
    "maxItems": N,
    "items": {
      "anyOf": [
        {
          "type": "integer",
          "minimum": J,
          "maximum": K
        },
        {
          "type": "null"
        }
      ]
    },
    "uniqueItems": true
  }
}

I am not sure how (or if it's even possible) to specify an array that applies the uniqueItems constraint to only a subset of the allowable items. I tried moving uniqueItems to lower levels of the schema with the hope that it might operate with restricted scope, but that doesn't work.

This might be possible using conditionals, but I haven't gone down that road yet since I'm not sure it will actually work, and I am hoping there is an easier approach that I have overlooked.

So, my question is: Is there a way to specify a JSON schema array that selectively enforces a uniqueness constraint only on the items that are not null ?

Answer 1

this is beyond the capabilities of uniqueItems and not a constraint JSON Schema is able to express. you will need to check this requirement elsewhere in your application's business logic.