Specify a value can be a string or null with JSON Schema

Question

Hopefully this isn't obvious to others because I find the docs at https://json-schema.org/ to be lacking in finer details. I'm getting a block of JSON with some properties that can be null or a string. How do you specify, in a JSON Schema (to be parsed by Json.NET's JsonSchema.Parse method), that a value can be of type null or type string?

Is there something simple I'm missing like supplying an array for the type? For example;

"member_region": { "type": [ "string", null ] } // this throws an exception

Also, does anyone have a better source for JSON Schema details than json-schema.org? Where can I find a larger selection of examples? I don't want to read a big document/specification to find something that can easily be demonstrated in a 10 line example.

Source with more examples and documentation: https://json-schema.org/understanding-json-schema/ which is linked in json-schema.org — nutsandbolts, Oct 19 '22 at 20:43

score 237 · Accepted Answer · edited Aug 25 '21 at 12:18

237

From https://json-schema.org/understanding-json-schema/reference/type.html

The type keyword may either be a string or an array:

If it’s a string, it is the name of one of the basic types above.

If it is an array, it must be an array of strings, where each string is the name of one of the basic types, and each element is unique. In this case, the JSON snippet is valid if it matches any of the given types

The same page lists also the defined data type names, including string and null.

Try:

"member_region": { "type": ["string", "null"] }

edited Aug 25 '21 at 12:18

Yirkha

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answered Apr 26 '13 at 16:52

Explosion Pills

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This is an updated link to the location in the current spec: – Demitri Mar 27 '21 at 18:16

zardilior · Answer 2 · 2020-08-31T01:07:50.207

89

Extending on Explosion Pills answer if you go for the array syntax:

"member_region": { "type": [ "string", "null" ] } // this works

because you are stating a type, not an example/value. You shouldn't go for:

 "member_region": { "type": [ "string", null ] } // this throws an exception

edited Aug 31 '20 at 01:07

answered Jun 21 '19 at 17:57

zardilior

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This is the only solution that works with schemas for Azure Logic Apps. – EricksonG Aug 05 '19 at 16:50
6

This solution is also recognized by Visual Studio Code. – ivosh Nov 08 '19 at 17:39

score 6 · Answer 3 · answered Jan 10 '23 at 13:54

6

anyOf may also be useful.

"member_region": {
  "anyOf": [
    { "type": "string" },
    { "type": "null" },
  ] 
}

answered Jan 10 '23 at 13:54

Epigene

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score -2 · Answer 4 · answered Apr 30 '21 at 13:42

-2

["string", "null"] will work if you're not using a RegEx pattern.

I'm using a date field validator:

    (0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])[- /.](19|20)\\d\\d

to allow a MM/dd/yyyy pattern, but it will throw a non-match error at an empty string ("")

answered Apr 30 '21 at 13:42

TheWizardOfTN

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An empty string is not equivalent to `null` in JSON. – Jason Desrosiers Apr 30 '21 at 16:54
Actually, I fixed this with this: ((0[1-9]|1[012])[- /.](0[1-9]|[12][0-9]|3[01])[- /.](19|20)\\d\\d )*? – TheWizardOfTN May 01 '21 at 19:29

Specify a value can be a string or null with JSON Schema

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