json schema validate empty array of objects

Question

var schema = {
  "$schema": "http://json-schema.org/draft-07/schema",
  "$id": "http://example.com/example.json",
  "type": "object",
  "required": [
    "data"
  ],
  "properties": {
    "data": {
      "$id": "#/properties/data",
      "type": "object",
      "required": [
        "id",
        "name",
        "description",
        "groups"
      ],
      "properties": {
        "id": {
          "$id": "#/properties/data/properties/id",
          "type": "integer"
        },
        "name": {
          "$id": "#/properties/data/properties/name",
          "type": "string"
        },
        "description": {
          "$id": "#/properties/data/properties/description",
          "type": "string"
        },
        "groups": {
          "$id": "#/properties/data/properties/groups",
          "type": "array",
          "items": {
            "$id": "#/properties/data/properties/groups/items",
            "anyOf": [
              {
                "$id": "#/properties/data/properties/groups/items/anyOf/0",
                "type": "object",
                "required": [
                  "id",
                  "name",
                  "description"
                ],
                "properties": {
                  "id": {
                    "$id": "#/properties/data/properties/groups/items/anyOf/0/properties/id",
                    "type": "integer"
                  },
                  "name": {
                    "$id": "#/properties/data/properties/groups/items/anyOf/0/properties/name",
                    "type": "string"
                  },
                  "description": {
                    "$id": "#/properties/data/properties/groups/items/anyOf/0/properties/description",
                    "type": "string"
                  }
                }
              }
            ]
          }
        }
      }
    }
  }
};

And I have json result either:

{
    "data": {
        "id": 1,
        "name": "Contacts",
        "description": "Pre-installed contacts management for your account.",
        "groups": []
    }
}

or

{
    "data": {
        "id": 4,
        "name": "Update Container Sub Type 913",
        "description": "I'll calculate the virtual SQL bus, that should circuit the FTP sensor!",
        "groups": [
            {
                "id": 1,
                "name": "tech",
                "description": "tech description group"
            }
        ]
    }
}

And when I validate json schema, the second - valid, the first - invalid. How can I resolve it to do both as valid?

A little simplification, side from the answer: you don't need all those $ids. They just specify the locations, so they're implicit. — gregsdennis
– gregsdennis, Commented Mar 16, 2021 at 7:34
Your schema is fine. See jsonschema.dev/s/s3K9o. I suspect something is wrong with the validator you're using. — gregsdennis
– gregsdennis, Commented Mar 16, 2021 at 9:46
Whatever tool you used to generate this schema did a terrible job. I highly suggest you don't use it anymore. Also, I second that your schema is correct. The validator you are using has a bug. — Jason Desrosiers
– Jason Desrosiers, Commented Mar 16, 2021 at 17:24

Yuri · Accepted Answer · 2025-01-31 11:31:31Z

3

As described in the JSON Schema Specification version 2020-12, it's possible to validate the minimum amount of items inside an array. Just use the property minItems.

You can write something like this:

{
    "$id": "#/properties/data/properties/groups",
    "type": "array",
    "minItems": 1,
    "items": {
       ...
    }
}

edited Jan 31 at 11:31

Yuri

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answered Jan 2, 2023 at 17:18

lbodevan

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Comments

jmbourdaret · Accepted Answer · 2021-03-16 19:06:29Z

2

edited: ** This does not answer the question **

Option 1 : Validators and Json-schema versions

edited: deleted wrong information.

Option 2 : discard the `anyOf`

The problem might be the anyOf: it means one or more of these , therefore, group cannot be empty. See the docs on json-schema.org for more info.

But why do you need an anyOf , when you only have one type of items ? Try :

 {
  "$schema": "http://json-schema.org/draft-07/schema#",

  "type": "object",
  "required": [
    "data"
  ],
  "properties": {
    "data": {
      "$id": "#/properties/data",
      "type": "object",
      "required": [
        "id",
        "name",
        "description",
        "groups"
      ],
      "properties": {
        "id": {
          "$id": "#/properties/data/properties/id",
          "type": "integer"
        },
        "name": {
          "$id": "#/properties/data/properties/name",
          "type": "string"
        },
        "description": {
          "$id": "#/properties/data/properties/description",
          "type": "string"
        },
        "groups": {
          "$id": "#/properties/data/properties/groups",
          "type": "array",
          "items": {
                "$id": "#/properties/data/properties/groups/items/anyOf/0",
                "type": "object",
                "required": [
                  "id",
                  "name",
                  "description"
                ],
                "properties": {
                  "id": {
                    "$id": "#/properties/data/properties/groups/items/anyOf/0/properties/id",
                    "type": "integer"
                  },
                  "name": {
                    "$id": "#/properties/data/properties/groups/items/anyOf/0/properties/name",
                    "type": "string"
                  },
                  "description": {
                    "$id": "#/properties/data/properties/groups/items/anyOf/0/properties/description",
                    "type": "string"
                  }
                }
          }
        }
      }
    }
  }
}

So you can get rid of the anyOf constraints , and validate an empty array as it is allowed by default.

Option 3 : conditional schemas

If your validator doesn't accept an empty array of anyOfs (some does) , There might be a possibility to work something out with conditional structures like if, then ... see reference. something in the lines of :

if array size is > 0 then apply the "anyOf" sub-schema

Please let us know how you solved this issue.

edited Mar 16, 2021 at 19:06

answered Mar 16, 2021 at 16:59

jmbourdaret

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4 Comments

Jason Desrosiers Over a year ago

No draft specifies that if a property is an array and is required that it needs to be non-empty. The issue you linked is about allowing the required keyword to be empty.

Jason Desrosiers Over a year ago

Also, while the reset of the answer isn't wrong, it is irrelevant because the schema is valid (other than the misuse of $ids). This is clearly a bug with the validator they are using.

jmbourdaret Over a year ago

Thanks @JasonDesrosier , I stand corrected. that explains a lot about most validators accepting empty arrays. May I ask, does it means that an array of anyOf can be empty too , despite the anyOf definition of 1+ ?

Jason Desrosiers Over a year ago

All the keywords that are defined to be an array of schemas, including anyOf, are defined to be non-empty.

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Option 2 : discard the `anyOf`