JSON Schema - Recursive Schema Definition

Question

I have a JSON Schema

{
    'description': 'TPNode',
    'type': 'object',
    'id': 'tp_node',
    'properties': {
        'selector': {
            'type': 'string',
            'required': true
        }, 
        'attributes': {
            'type': 'array',
            'items': {
                'name': 'string',
                'value': 'string'
            }
        },
        'children': {
            'type': 'array',
            'items': {
                'type': 'object',
                '$ref': '#'
            }
        },
        'events': {
            'type': 'array',
            'items': { 
                'type': 'object',
                'properties': {
                    'type': {
                        'type': 'string'
                    },
                    'handler': {
                        'type': 'object'
                    },
                    'dependencies': {
                        'type': 'array',
                        'items': {
                            'type': 'string'
                        }
                     }
                 }
            }
        }
    }
}

What I'm trying to express in the children property is that it's an array of objects with the same exact schema. Is this the correct way to describe it?

Why are you using v3 syntax? `"required"` is an array in v4. — cloudfeet, Dec 24 '13 at 01:20
You are correct. However, I'm validating schema via JSON.NET which, as I found out, does not support v4 syntax. — William, Dec 24 '13 at 01:50

score 25 · Answer 1 · edited Nov 09 '16 at 08:35

25

Yes, your schema will work. The "$ref": "#" points back to the root of the schema document.

However, the "type": "object" is useless:

{
    'type': 'object',
    '$ref': '#'
}

If $ref is present, then all other keywords are ignored. It would be better to remove type from the #/properties/children/items schema.

edited Nov 09 '16 at 08:35

krisanalfa

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answered Dec 24 '13 at 01:15

cloudfeet

12,156
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score 22 · Accepted Answer · answered Dec 24 '13 at 00:18

22

Use the id of the schema you need to reference

'$ref': 'tp_node'

See here: http://json-schema.org/latest/json-schema-core.html#anchor30

answered Dec 24 '13 at 00:18

Sergey Eremin

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3

The solution proposed in the question (using `"$ref": "#"`) is actually better, because it works even if the schema is moved/renamed. With your solution, if you rename the schema then you need to alter a bunch of references which *could* be internal instead. – cloudfeet Dec 24 '13 at 01:17
4

This solution is preferable and should be the accepted one; in case of a change in the schema it breaks cleanly and obviously, as opposed to the more general one using `"$ref": "#"` with which changes are likely to produce harder to diagnose errors. – Peace Makes Plenty Jan 05 '14 at 09:48
Coming late into this, by pointing at itself will cause a circular reference error and I read somewhere it is not recommended to do so. But interesting enough I found this [github](https://github.com/json-schema-org/json-schema-spec/issues/279). I wish i can do that too, maybe it is the version of the schema I used (draft-6). – roger May 27 '19 at 12:45

score 9 · Answer 3 · answered Sep 13 '19 at 15:52

Recursion example.

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

  "definitions": {
    "person": {
      "type": "object",
      "properties": {
        "name": { "type": "string" },
        "children": {
          "type": "array",
          "items": { "$ref": "#/definitions/person" },
          "default": []
        }
      }
    }
  },

  "type": "object",

  "properties": {
    "person": { "$ref": "#/definitions/person" }
  }
}

score 8 · Answer 4 · edited Nov 09 '16 at 08:34

use definitions and $ref.

You can copy and paste the following schema to this online json/schema editor and check the results.

editor screenshot:

schema code:

{
    "definitions": {
        "TPNode": {
            "title": "TPNode",
            "description": "TPNode",
            "type": "object",
            "properties": {
                "selector": {
                    "type": "string",
                    "required": true
                }, 
                "attributes": {
                    "type": "array",
                    "items": {
                        "title": "Attribute",
                        "type": "object",
                        "properties": {
                            "name": {
                                "type": "string"
                            },
                            "value": {
                                "type": "string"
                            }
                        }
                    }
                },
                "children": {
                    "type": "array",
                    "items": {
                        "$ref": "#/definitions/TPNode"
                    }
                },
                "events": {
                    "type": "array",
                    "items": { 
                        "title": "Event",
                        "type": "object",
                        "properties": {
                            "type": {
                                "type": "string"
                            },
                            "handler": {
                                "type": "object"
                            },
                            "dependencies": {
                                "type": "array",
                                "items": {
                                    "type": "string"
                                }
                            }
                        }
                    }
                }
            }
        }
    },
    "$ref": "#/definitions/TPNode"
}

JSON Schema - Recursive Schema Definition

4 Answers4

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