springdoc-openapi spec generation for inheritance witth generics - swagger

Question

I have a Spring Boot (kotlin) project for which I use springdoc-openapi to generate OpenApi 3 spec. My data model looks like so:
open class Animal
data class Cat(val catName: String) : Animal()
data class Dog(val dogName: String) : Animal()
open class Food<T : Animal>
class CatFood : Food<Cat>()
class DogFood : Food<Dog>()
and a simple controller like so:
#GetMapping("/test")
fun test(): Food<out Animal> = DogFood()
for which the generated yaml is:
openapi: 3.0.1
info:
title: OpenAPI definition
version: v0
servers:
- url: http://localhost:8085
paths:
/test:
get:
tags:
- test-controller
operationId: test
responses:
"200":
description: default response
content:
'*/*':
schema:
$ref: '#/components/schemas/FoodAnimal'
components:
schemas:
FoodAnimal:
type: object
The problem here is that my controller can return either DogFood or CatFood, and that is specified in the return type. The schema I would expect to be generated is:
openapi: 3.0.1
info:
title: OpenAPI definition
version: v0
servers:
- url: http://localhost:8085
paths:
/test:
get:
tags:
- test-controller
operationId: test
responses:
"200":
description: default response
content:
'*/*':
schema:
oneOf:
- $ref: '#/components/schemas/FoodAnimal'
- $ref: '#/components/schemas/DogFood'
- $ref: '#/components/schemas/CatFood'
components:
schemas:
FoodAnimal:
type: object
CatFood:
allOf:
- $ref: '#/components/schemas/FoodAnimal'
type: object
DogFood:
allOf:
- $ref: '#/components/schemas/FoodAnimal'
type: object
Is there some way to achieve this?

Answer 1

For inheritance, you just need to add #Schema annotation, on your parent class:
#Schema(
type = "object",
title = "Food",
subTypes = [CatFood::class, DogFood::class]
)
open class Food<T : Animal>
class CatFood : Food<Cat>()
class DogFood : Food<Dog>()
If you need a reponse using oneOf, you will have to add #Response:
#GetMapping("/test")
#ApiResponse(content = [Content(mediaType = "*/*", schema = Schema(oneOf = [Food::class, CatFood::class,DogFood::class]))])
fun test(): Food<out Animal> = DogFood()

Answer 2

I had problems using OpenApi with inheritance for nested properties.
I used JsonSubtype annotations and generics as a workaround.
data class AnimalResponse<FoodResponse>(
val id: UUID,
val eats: FoodResponse
)
#JsonSubTypes(value = [
JsonSubTypes.Type(
value = CatFoodResponse::class,
name = "CAT_FOOD"
), JsonSubTypes.Type(
value = DogFoodResponse::class,
name = "DOG_FOOD"
)])
interface FoodResponse
This will show all types of FoodResponses in AnimalResponse Schema.