JSON Schema: validate a number-or-null value

Question

Is there a way to enable a JSON schema property to be either a number or null?

I am building an API which contains a heading attribute. Can be a number between 0 (inclusive) and 360 (exclusive), or null, so the following inputs are OK:

{"heading": 5}
{"heading": 0}
{"heading": null}
{"heading": 12}
{"heading": 120}
{"heading": null}

And the following inputs are erroneous:

{"heading": 360}
{"heading": 360.1}
{"heading": -5}
{"heading": false}
{"heading": "X"}
{"heading": 1200}
{"heading": false}

Addendum:

anyOf is clearly the right answer. Adding the full schema for clarity.

Schema

{
    "$schema": "http://json-schema.org/draft-04/schema#",
    "type": "object",
    "additionalProperties": false,
    "properties": {
      "heading": {
        "anyOf": [
          {"type": "number"},
          {"type": "null"}
        ]
      }
    }
}

Asked By: Adam Matan

||

Source

Answer 1

The trick is using a type array. Instead of:

"type": "number"

Use:

"type": ["number", "null"]

The following code enforces a number-or-null policy, plus numerical restrictions if the value is a number:

from jsonschema import validate
from jsonschema.exceptions import ValidationError
import json

schema=json.loads("""{
  "$schema": "http://json-schema.org/schema#",
  "description": "Schemas for heading: either a number within [0, 360) or null.",
  "title": "Tester for number-or-null schema",
  "properties": {
    "heading": {
      "type": ["number", "null"],
      "exclusiveMinimum": false,
      "exclusiveMaximum": true,
      "minimum": 0,
      "maximum": 360
    }
  }
}""")

inputs = [
{"heading":5}, {"heading":0}, {"heading":360}, {"heading":360.1},
{"heading":-5},{"heading":None},{"heading":False},{"heading":"X"},
json.loads('''{"heading":12}'''),json.loads('''{"heading":120}'''),
json.loads('''{"heading":1200}'''),json.loads('''{"heading":false}'''),
json.loads('''{"heading":null}''')
]

for input in inputs:
    print "%-30s" % json.dumps(input),
    try:
        validate(input, schema)
        print "OK"
    except ValidationError as e:
        print e.message

Which gives:

{"heading": 5}                 OK
{"heading": 0}                 OK
{"heading": 360}               360.0 is greater than or equal to the maximum of 360
{"heading": 360.1}             360.1 is greater than or equal to the maximum of 360
{"heading": -5}                -5.0 is less than the minimum of 0
{"heading": null}              OK
{"heading": false}             False is not of type u'number', u'null'
{"heading": "X"}               'X' is not of type u'number', u'null'
{"heading": 12}                OK
{"heading": 120}               OK
{"heading": 1200}              1200.0 is greater than or equal to the maximum of 360
{"heading": false}             False is not of type u'number', u'null'
{"heading": null}              OK

Answered By: Adam Matan

Answer 2

In draft-04, you would use the anyOf directive:

{
  "anyOf": [
    {
      "type": "number",
      "minimum": 0,
      "maximum": 360,
      "exclusiveMaximum": true
    },
    {
      "type": "null"
    }
  ]
}

You could also use “type”: [“number”, “null”] as Adam suggests, but I think anyOf is cleaner (as long as you use a draft-04 implementation), and ties the minimum and maximum declaration to the number explicitly.

Disclaimer: I don’t know anything about the python implementation, my answer is about json schema.

Answered By: fiddur

JSON Schema: validate a number-or-null value

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