JSON Schema with unknown property names

Question

I want to have a JSON Schema with unknown property names in an array of objects. A good example is the meta-data of a web page:

      "meta": {
        "type": "array",
        "items": {
          "type": "object",
          "properties": {
            "unknown-attribute-1": {
              "type": "string"
            },
            "unknown-attribute-2": {
              "type": "string"
            },
            ...
          }
        }
      }

Any ideas please, or other way to reach the same?

Solution 1

Use patternProperties instead of properties. In the example below, the pattern match regex .* accepts any property name and I am allowing types of string or null only by using "additionalProperties": false.

  "patternProperties": {
    "^.*$": {
      "anyOf": [
        {"type": "string"},
        {"type": "null"}
      ]
    }
  },
  "additionalProperties": false

... or if you just want to allow a string in your "object" (like in the original question):

  "patternProperties": {
    "^.*$": {
        {"type": "string"},
    }
  },
  "additionalProperties": false

Solution 2

You can make constraints on properties not explicitly defined. The following schema enforces "meta" to be an array of objects whose properties are of type string:

{
    "properties" : {
        "meta" : {
            "type" : "array",
            "items" : {
                "type" : "object",
                "additionalProperties" : {
                    "type" : "string"
                }
            }
        }
    }
}

In case you just want to have an array of strings, you may use the following schema:

{
    "properties" : {
        "meta" : {
            "type" : "array",
            "items" : {
                "type" : "string"
            }
        }
    }
}

Comments

[Alexey Sh.]

I'm getting error "Property 'patternProperties' is not allowed".

[pink spikyhairman]

@AlexeySh. please post your full JSON and I will take look

[Alexey Sh.]

exactly copypaste of your answer

[pink spikyhairman]

@AlexeySh. my first guess would be if you're using JSON Schema or OpenAPI. If JSON Schema, then you should use a recent version. If OpenAPI, a bit of Googling shows patternProperties did not get into OpenAPI as of version 3. Maybe there's a later version.

[Alexey Sh.]

it seems like because I was using swagger and it doesn't support the latest schema

[redDevil]

this did work me, but without the anyOf and additionalProperties as well