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

89
votes

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.

3
jsonjson.netjsonschema

3 Answers

129
votes

From http://json-schema.org/latest/json-schema-validation.html#anchor79

The value of this keyword MUST be either a string or an array. If it is an array, elements of the array MUST be strings and MUST be unique.

String values MUST be one of the seven primitive types defined by the core specification.

Then we refer to types: http://json-schema.org/latest/json-schema-core.html#anchor8

It lists string and null. Try:

"member_region": { "type": ["string", "null"] }
69
votes

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
-2
votes

["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 ("")