[BUG][KOTLIN] oneOf does not generate type hierarchy correctly

[jensbaitingerbosch]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When having an endpoint that returns R being oneOf a or b (or more), the generated classes for A and B do not implement the generated interface which is generated for R and therefore the deserialization with Jackson fails.

openapi-generator version

7.14.0 (gradle plugin)

OpenAPI declaration file content or url

---
openapi: 3.0.1
info:
  title: some
  version: 1.0.0
servers:
  - url: http://localhost:8080
    description: Local server


paths:
  "/someEndponint":
    get:
      summary: Get the specified device job of a single device
      description: |
        Obtain a specified device job of a single device

      operationId: someEndpoint
      responses:
        '200':
          description: Success
          content:
            application/json:
              schema:
                oneOf:
                  - "$ref": "#/components/schemas/A"
                  - "$ref": "#/components/schemas/B"
                discriminator:
                  propertyName: jobType
                  mapping:
                     A: "#/components/schemas/A"
                     B: "#/components/schemas/B"
components:
  schemas:
    A:
      type: object
      properties:
        jobType:
          type: string
        propertyA:
          type: string

    B:
      type: object
      properties:
        jobType:
          type: string
        propertyB:
          type: string

Generation Details

here is the plugin configuration:

tasks.register<GenerateTask>("openApiGenerateV2Client") {
        generatorName = "kotlin" 
        inputSpec = "$projectDir/src/main/resources/static/v2/open-api-docs.yaml"
        outputDir = "${layout.buildDirectory.get()}/generated/client/"
        configOptions =
            mapOf(
                "library" to "jvm-spring-restclient",
                "serializationLibrary" to "jackson",
                "useSpringBoot3" to "true",
            )
    }

Steps to reproduce

have a server that implement specified interface, call the client method, it produces the following Exception:

Caused by: com.fasterxml.jackson.databind.exc.InvalidTypeIdException: Could not resolve type id 'A' as a subtype of `...SomeEndpoint200Response`: Class `...A` not subtype of `...SomeEndpoint200Response`
 at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 12]
	at com.fasterxml.jackson.databind.exc.InvalidTypeIdException.from(InvalidTypeIdException.java:43)
	at com.fasterxml.jackson.databind.DeserializationContext.invalidTypeIdException(DeserializationContext.java:2096)
	at com.fasterxml.jackson.databind.jsontype.impl.TypeDeserializerBase._findDeserializer(TypeDeserializerBase.java:198)
	at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer._deserializeTypedForId(AsPropertyTypeDeserializer.java:150)
	at com.fasterxml.jackson.databind.jsontype.impl.AsPropertyTypeDeserializer.deserializeTypedFromObject(AsPropertyTypeDeserializer.java:135)
	at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserializeWithType(AbstractDeserializer.java:262)
	at com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:74)
	at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:342)

Here the generated Code

data class A (

    @get:JsonProperty("jobType")
    val jobType: kotlin.String? = null,

    @get:JsonProperty("propertyA")
    val propertyA: kotlin.String? = null

)

data class B (

    @get:JsonProperty("jobType")
    val jobType: kotlin.String? = null,

    @get:JsonProperty("propertyB")
    val propertyB: kotlin.String? = null

) 

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "jobType", visible = true)
@JsonSubTypes(
)

interface SomeEndpoint200Response {

    @get:JsonProperty("jobType")
    val jobType: kotlin.String?
    @get:JsonProperty("propertyA")
    val propertyA: kotlin.String?
    @get:JsonProperty("propertyB")
    val propertyB: kotlin.String?

}

Related issues/PRs

Suggest a fix

How the code should be generated (note, the Java generator creates a similar structure):

data class A : SomeEndpoint200Response (

    @get:JsonProperty("jobType")
    override val jobType: kotlin.String? = null,

    @get:JsonProperty("propertyA")
    val propertyA: kotlin.String? = null

)

data class B : SomeEndpoint200Response (

    @get:JsonProperty("jobType")
   override val jobType: kotlin.String? = null,

    @get:JsonProperty("propertyB")
    val propertyB: kotlin.String? = null

) 

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "jobType", visible = true)
@JsonSubTypes(
)

interface SomeEndpoint200Response {

    @get:JsonProperty("jobType")
    val jobType: kotlin.String?

}

[Mattias-Sehlstedt]

Could you please provide a specification that would generated your example code so that the issue is reproducible? Could you also state what generator that you are using for Kotlin?

The generic Kotlin generator does not seem to state that it offer oneOf support?

[Mattias-Sehlstedt]

With a regular oneOf relation between the parent (Inline model SomeEndpoint200Response in this case) and the children (A and B) it is not intuitive to achieve a structure where override val jobType can be deduced. This since there is no explicit relation between the child and the parent (the parent refers to the child, but there is no mutual recognition). For this one would need to have it so that the children refers to the parent with an allOf.

This is an issue since the override keyword is dependent on the isInherited CodegenProperty. As far as I am aware it should not be set to true for the schema above, since that would break the usage of A outside the context of the oneOf (e.g., an endpoint that returns a pure A model).

Would the generated code be invalid if we had

data class A : SomeEndpoint200Response (

    @get:JsonProperty("jobType")
    val jobType: kotlin.String? = null,

    @get:JsonProperty("propertyA")
    val propertyA: kotlin.String? = null

)

data class B : SomeEndpoint200Response (

    @get:JsonProperty("jobType")
    val jobType: kotlin.String? = null,

    @get:JsonProperty("propertyB")
    val propertyB: kotlin.String? = null

) 

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "jobType", visible = true)
@JsonSubTypes(
)

interface SomeEndpoint200Response {

    @get:JsonProperty("jobType")
    val jobType: kotlin.String?

}

[dennisameling]

Here's a PR that adds polymorphism, oneOf and allOf support to the kotlin-server generator: #22610. I think it does what you're looking for here.

Although this issue is for the kotlin generator, if the PR for kotlin-server gets accepted, I'd be happy to add the same functionality to the kotlin generator as well.