Swagger Yaml schema definition for object without a fixed property list

Question

I am implementing an API-first application with the help of Swagger. One of the most important objects to be returned is a DICOM object, which returns a collection of attributes with flexible names, for example:

{ 
  "00080005": {"vr":"CS","Value":["ISO_IR 100"]},
  "00080020": {"vr":"DA","Value":["20160602"]},
  "00080030": {"vr":"TM","Value":["171855.7490"]},
  "00080050": {"vr":"SH","Value":["1234"]},
  "00080090": {"vr":"PN","Value":[{"Alphabetic":"Parikh MD^Anush^M"}]}
}

So I cannot know the name of all the attributes in advance (00080005, 00080030, etc.) although the file structure is very uniform.

My concrete question is: what would be the schema definition for such JSON document.

I have tried the following without success:

definitions:
  DicomMetadataJson:
    type: object
    patternProperties:
      ^\d{8}:
        type: object      

but the Swagger Editor returns an error like:

code: "OBJECT_ADDITIONAL_PROPERTIES"

message: "Additional properties not allowed: patternProperties"

description: "A deterministic version of a JSON Schema object."

Answer 1

OpenAPI (fka. Swagger) use only a subset of JSON Schema v4 which, unfortunately, do not propose patternProperties.

But given the provided example is a map, you can describe it using additionalProperties:

swagger: "2.0"
info:
  version: 1.0.0
  title: Hashmap

paths: {}

definitions:
  DicomMetadataJson:
    additionalProperties:
      properties:
        vr:
          type: string
        Value:
          type: array
          items:
            type: string

The key is not defined and is supposed to be a string (therefore you cannot enforce it's format).

Note that SwaggerUI Swagger UI do not render them for now.The issue is tracked here https://github.com/swagger-api/swagger-ui/issues/1248

In the meanwhile you can use this trick define a non required property (default in the example below) of the same type of the map's objects and give some hint within the description:

swagger: "2.0"
info:
  version: 1.0.0
  title: Hashmap

paths: {}

definitions:
  MetaData:
    properties:
      vr:
        type: string
      Value:
        type: array
        items:
          type: string

  DicomMetadataJson:
    description: 'A <string,MetaData> map, default key is only for documentation purpose'
    properties:
      default:
        $ref: '#/definitions/MetaData'
    additionalProperties:
      $ref: '#/definitions/MetaData'

Concerning the quote The schema exposes two types of fields. Fixed fields, which have a declared name, and Patterned fields, which declare a regex pattern for the field name. Patterned fields can have multiple occurrences as long as each has a unique name., it concerns the format of the OpenAPI specification itself and not the objects used by the API described with an OpenAPI specification.