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?

The meta-data is an array of object, where I don't know the possible names of the attributes of the objects — Thami Bouchnafa, Aug 17 '15 at 10:59
Which constraints do you want to enforce to your unnamed properties? Do you want them to have some type, or do you want their names to follow some pattern? You can have unknown property names in JSON schema provided you do not have additionalProperties=false — jruizaranguren, Aug 17 '15 at 11:34
yes, I want to enforce them to be of type "string" The names do not have to match any pattern — Thami Bouchnafa, Aug 17 '15 at 11:37
Have a look [at this answer](https://stackoverflow.com/a/26848488/5663986) for a much much simpler way of achieving this compared to what suggested below. — belvederef, May 07 '20 at 11:26

score 129 · Answer 1 · edited Nov 25 '21 at 09:49

129

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

edited Nov 25 '21 at 09:49

Jean-Francois T.

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answered Feb 20 '17 at 15:31

pink spikyhairman

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I'm getting error "Property 'patternProperties' is not allowed". – Alexey Sh. Sep 15 '20 at 15:24
@AlexeySh. please post your full JSON and I will take look – pink spikyhairman Sep 16 '20 at 14:55
exactly copypaste of your answer – Alexey Sh. Sep 17 '20 at 08:56
@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. – pink spikyhairman Sep 18 '20 at 17:53
it seems like because I was using swagger and it doesn't support the latest schema – Alexey Sh. Sep 21 '20 at 13:43
this did work me, but without the `anyOf` and `additionalProperties` as well – redDevil Oct 28 '21 at 14:22
Yes, there seems to be an extra pair of braces in the second example. – Rubem Pechansky Jul 12 '23 at 21:14

jruizaranguren · Answer 2 · 2015-08-17T20:13:45.323

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"
            }
        }
    }
}

score 1 · Answer 3 · answered Aug 21 '15 at 11:02

The Solution of @jruizaranguren works for me. Though I am the same who defines the schema, i choosed another solution

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

I converted the object to an array of name-value objects An example of a valid JSON:

"meta": [
    [
      {
        "name": "http-equiv",
        "value": "Content-Type"
      },
      {
        "name": "content",
        "value": "text/html; charset=UTF-8"
      }
    ],
    [
      {
        "name": "name",
        "value": "author"
      },
      {
        "name": "content",
        "value": "Astrid Florence Cassing"
      }
    ]
  ]

JSON Schema with unknown property names

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