Loading Valid Values from Another JSON File

I would like to create a JSON schema that defines two entities: region and country.

The JSON schema for country is as follows:

{
   "$id":"https://example.com/arrays.schema.json",
   "$schema":"http://json-schema.org/draft-07/schema#",
   "description":"A list of countries",
   "type":"array",
   "items":{
      "type":"object",
      "required":[
         "code",
         "name"
      ],
      "properties":{
         "code":{
            "type":"string",
            "maxLength": 2,
            "minLength": 2
         },
         "name":{
            "type":"string",
         }
      }
   }
}

This allows me to define countries in a file, lets call it countries.json:

[
  { "code": "GB", "name": "United Kingdom"},
  { "code": "US", "name": "United States of America"}
]

I would now like to define a schema for region. Here is an example file that I would consider valid:

[
  { "name": "Europe", "countries": [ "GB" ] },
  { "name": "North America", "countries": [ "US" ] }
]

The countries attribute needs to be validated against the contents of countries.json. How can this be achieved? I do not want to use the enum type and repeat the list of countries in the region schema

JSON Schema can only validate using values in a schema. You can't arbitrarily query some non-schema JSON such as countries.json to get the allowed values. I suggest doing something like writing a script that generates an country code enum schema from countries.json and then referencing that schema in your regions schema. You'd end up with something like this,

{
  "$id":"https://example.com/countries.schema.json",
  "$schema":"http://json-schema.org/draft-07/schema#",

  ... the schema from the question ...
}

{ // generated from countries.json
  "$id":"https://example.com/country-codes.schema.json",
  "$schema":"http://json-schema.org/draft-07/schema#",

  "enum": ["GB", "US", ...]
}

{
  "$id":"https://example.com/region.schema.json",
  "$schema":"http://json-schema.org/draft-07/schema#",

  "type": "object",
  "properties": {
    "name": { "type": "string" },
    "countries": { "$ref": "country-codes.schema.json" }
  }
}