Openapi-specification: Support for Constant Value in API

[duckladydinh]

Since OpenAPI can be used to generate client code, it is good to support some constant value in the API itself.

Use case: When you add type info to a class as a properties, we need that property for deserialization and the value of this property will never change.

[MikeRalphson]

Can you not do this with an enum property which only has one value?

MySchema:
  type: object
  properties:
    MyProperty:
      type: string
      enum:
      - constantValue

[hkosova]

Possibly related: #1313

[marcusbesjes]

Can you not do this with an enum property which only has one value?

Yes thats how it needs to be done now, but it's a bit verbose and it doesn't look nice in your documentation (generated web pages), where it will show as an expandable list of one item VS just the string value.

[MikeRalphson]

Closing, as this is a dupe of #1313 as @hkosova observed.