JSON schema validation for null when "type"="string"

Question

I wanted to prevent a json filed from allowing null as a valid value for it. Tried using the keyword not, but no luck.

Want the below json to be validated as false, as the field stats as value as null.

{
  "stats": "null"
}

please find my schema below:-

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "id": "http://jsonschema.net#",
  "type": "object",
  "additionalProperties": false,
  "maxProperties": 1,
  "properties": {
    "stats": {
      "id": "http://jsonschema.net/stats#",
      "type": "string",
      "maxLength": 5,
      "minLength": 2,
      "additionalProperties": false,
      "maxProperties": 1,
      "not": {"type":  "null"}
    }
  },

  "required": [
    "stats"
  ]
}

Though i gave "not": {"type": "null"}, it still validated successfully.

I tried validating with `{ "stats" : "null" }` and it failed. How are you validating your JSON? — Tim Biegeleisen, Jun 25 '15 at 05:16
Are you sure it's "null" not 'null'? For this is a String, not a 'null' value — Danielson, Jun 25 '15 at 05:32
I am using java code to validate the json, with jsonSchema.But I am checking the validation using http://jsonschemalint.com/draft4/#, to test in amuch easier way. — Manu, Jun 25 '15 at 05:32

score 9 · Accepted Answer · answered Sep 08 '17 at 15:54

Wow. So much confusion here.

The problem is simple:

{
  "stats": "null"
}

"null" is a string, thus it’s valid (because you allow strings). This would not be allowed by your schema, which works as you expect:

{
    stats: null
}

The answer from Ashish Patil is wrong: in your schema (not your data), when you are specifying the type, the type name is a string. Specifying "not": {"type": null} is not valid. You could specify "not": {"type": "null"}, but that would be redundant as the earlier "type": "string" already implies that.

The accepted answer from jruizaranguren works because it doesn’t allow the string "null". It doesn’t address the core confusion that null is not the same as "null".

score 3 · Answer 2 · answered Jun 25 '15 at 07:04

3

You can use "enum" keyword instead of "type". "null" is not a valid json and json-schema type.

Also additionalProperties and maxProperties are useless within stats description.

{
    "$schema" : "http://json-schema.org/draft-04/schema#",
    "id" : "http://jsonschema.net#",
    "type" : "object",
    "additionalProperties" : false,
    "maxProperties" : 1,
    "properties" : {
        "stats" : {
            "id" : "http://jsonschema.net/stats#",
            "type" : "string",
            "maxLength" : 5,
            "minLength" : 2
            "not" : {
                "enum" : ["null"]
            }

        }
    }, 
    "required" : [
        "stats"
    ]
}

answered Jun 25 '15 at 07:04

jruizaranguren

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Thanks jruizaranguren. Works perfect – Manu Jun 25 '15 at 08:27
The word `enum` is not instead of "type", it goes along with it and defines set of possible values – Nick Roz Nov 11 '22 at 22:42
That's True. It was a bad sentence. – jruizaranguren Nov 13 '22 at 19:35

score 3 · Answer 3 · answered Jun 25 '15 at 07:25

First of all, null is not a String. So try using below in your schema--

 "stats": {
  "id": "http://jsonschema.net/stats#",
  "type": "string",
  "maxLength": 5,
  "minLength": 2,
  "additionalProperties": false,
  "maxProperties": 1,
  "not": {"type":  null}
}

But, in the example snippet you have mentioned something like below--

{ "stats": "null" }

So, if you really wanted null to be not allowed in your file, then your example file should look like { "stats": null } Along schema i have provided.

JSON schema validation for null when "type"="string"

3 Answers3