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"}         ]       }     } } 

Answer 1

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.

Answer 2

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