How to reuse swagger 2.0 string pattern definition?

I'm defining the following in swagger 2.0 "definition" section. I first defined the format of timestamp that I would use in many object's properties for different purposes, such as created timestamp and last updated timestamp.

definitions:
  TimeStamp:
    title: Timestamp format
    description: ISO 8681, "2016-08-18T17:33:00Z"
    type: string
    pattern: \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z
  Application:
    title: An application
    type: object
    properties:
      cDtm:
        title: Creation timestamp
        description: Some description
        type: string
        pattern:\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z

However, when defining the "cDtm" property of the "Application" object, I cannot find a way to reuse the timestamp definition. If I use "$ref" along with "title" and "description", I get a warning "sibling values are not allowed alongside '$ref'". If I don't use "$ref", I need to repeat the type and pattern definition as above.

So, my question is, is there a way to use $ref to reuse a string pattern definition but still able to give the defined property a new title and description?

Thanks!

Bing

Solution

OpenAPI Specification includes built-in format: date-time for this format, so you don't actually need a pattern here. Instead, use:

type: string
format: date-time

If, for some reason, you want to stick with the pattern, you can use the following workaround. Basically, you can "add" properties to a $ref if you wrap the $ref into allOf. This works in Swagger Editor and Swagger UI, but other tooling support may vary.

  Application:
    title: An application
    type: object
    properties:
      cDtm:
        title: Creation timestamp
        description: Some description

        allOf:
          - $ref: '#/definitions/TimeStamp'

Also keep in mind that pattern works as a partial match by default. To force an exact match, enclose the pattern expression into ^..$:

pattern: ^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z$