[JAVA] Use interfaces in model when not using discriminator for inheritance?

[JLLeitschuh]

Description

If you choose not to use inheritance in your model and instead simply use composition using the allOf properties, does it make sense to generate interfaces for these models so that the server implementation can have code reuse for specific types?

Use case for not relying upon inheritance:
Inheritance makes the API more confusing for consumers in untyped languages. In our use case, our consumers primarily use untyped languages but our server is written in strongly typed java.

Swagger-codegen version

A version just a few commits after the 2.2.2 release.

Swagger declaration file content or url

For example:

definitions:

  ModelOne:
    type: object
    properties:
      modelOneProp:
        type: string

  ModelTwo:
    type: object
    properties:
      modelTwoProp:
        type: string

  ModelThree:
    type: object
    properties:
      modelThreeProp:
        type: string

  SimpleComposition:
    allOf:
      - $ref: '#/definitions/ModelOne'
      - $ref: '#/definitions/ModelTwo'
      - type: object
        properties:
          simpleCompositionProp:
            type: string

  CompositionOfSimpleComposition:
      allOf:
        - $ref: '#/definitions/SimpleComposition'
        - $ref: '#/definitions/ModelThree'
        - type: object
          properties:
            compositionOfSimpleCompositionProp:
              type: string

Suggest a Fix

In the above example additional interfaces would be generated (names are up for debate):
IModelOne, IModelTwo, IModelThree ISimpleComposition, ICompositionOfSimpleComposition.

The class ModelOne would implement IModelOne as would SimpleComposition and ISimpleComposition.

Ect...

What are the maintainers thoughts on this? Would this be a feature worth implementing in the mainline branch?

[wing328]

I remember that's a similar discussion before but I can't find it now. I'll try to dig it out tomorrow.

[JLLeitschuh]

Thanks, this is something that we are considering implementing for our generator and would contribute to this project if it seemed useful.

[JLLeitschuh]

The nice thing about this change is that it wouldn't be API breaking.
It would be simply adding to the existing model objects.

Does the super type exist in a variable in the mustache files still if the discriminator isn't used or would it require some back end wiring in Java to get this to work?

[wing328]

I think what you suggested is relevant to #2096 (comment)

[wing328]

Does the super type exist in a variable in the mustache files still if the discriminator isn't used or would it require some back end wiring in Java to get this to work?

Probably the latter if I remember correctly

[cbornet]

ModelOne and ModelTwo could be objects that you actually want to instanciate (eg. they are the response to an operation). So I don't think this is doable. Also I don't see what you would gain since you would still need to implement the getter/setters in the class.