JSON Schema to validate interdependent array structure

Question

I am trying to write a schema validating arrays with the following structural constraints:

it can only ever contain the values 1,2,3,4,5
if the array contains a 1, that must be the only entry
the array can only contain either 2, 3 or 4 at the same time, so e.g. [2,3] is not allowed
5 can be present together with 2,3,4

so the valid arrays are

[1],
[2],
[3],
[4],
[5],
[2,5],
[3,5],
[4,5]

I started writing a schema as follows:

{
    "type": "array",
    "oneOf": [
        { "items": { "enum": [1] } },
        {
            "anyOf": [
                ???
            ]
        }
    ]
}

I can't get the ??? part to work. Is it possible at all? NOTE: I would like to avoid hardcoding all possible arrays, as I have to validate more complex structures - this is only an example. Also, the optimum is a solution using only anyOf, allOf, oneOf, not, avoiding keywords like minItems

Jason Desrosiers · Accepted Answer · 2017-06-19 16:21:22Z

1

This passes all of your constraints.

{
  "type": "array",
  "anyOf": [
    { "enum": [[1]] },
    {
      "items": { "enum": [2, 3, 4, 5] },
      "oneOf": [
        { "$ref": "#/definitions/doesnt-contain-2-3-or-4" },
        { "$ref": "#/definitions/contains-2" },
        { "$ref": "#/definitions/contains-3" },
        { "$ref": "#/definitions/contains-4" }
      ]
    }
  ],
  "definitions": {
    "doesnt-contain-2-3-or-4": {
      "items": { "not": { "enum": [2, 3, 4] } }
    },
    "contains-2": {
      "not": {
        "items": { "not": { "enum": [2] } }
      }
    },
    "contains-3": {
      "not": {
        "items": { "not": { "enum": [3] } }
      }
    },
    "contains-4": {
      "not": {
        "items": { "not": { "enum": [4] } }
      }
    }
  }
}

If you have the option of using the new draft-06 keywords contains and const, it's actually a pretty clean solution. There is a little duplication, but I don't think that can be helped.

{
  "type": "array",
  "anyOf": [
    { "const": [1] },
    {
      "items": { "enum": [2, 3, 4, 5] },
      "oneOf": [
        { "not": { "contains": { "enum": [2 ,3, 4] } } },
        { "contains": { "const": 2 } },
        { "contains": { "const": 3 } },
        { "contains": { "const": 4 } }
      ]
    }
  ]
}

edited Jun 19, 2017 at 16:21

answered Jun 18, 2017 at 5:57

Jason Desrosiers

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4 Comments

Jason Desrosiers Over a year ago

@tscherg It's an enum that contains a single value and that value is [1]. It's the simplest way to say that 1 must stand alone. This works because enum is not limited to simple types.

tscherg Over a year ago

I'll accept your answer, thanks again. I've had a quick look around and there seem to be no v6 validators for PHP around yet. Did you come across one?

Jason Desrosiers Over a year ago

@tscherg The only validator I've seen in any language that supports draft-06 is ajv, but that's for JavaScript. Hopefully there is someone out there working on one for PHP

tscherg Over a year ago

I know that the folks over at github.com/justinrainbow/json-schema are currently reviewing the PR for v6 validation. Seems they are close, but not quite there yet

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