[JAVA] Discriminator not used in JSON.java

[gravelld]

Description

When I generate client libs for an OpenAPI 3.0.1 YAML, discriminator settings are ignored in the generated JSON deserialisation code.

This means when deserialising JSON we can't enforce polymorphism/composition.

Swagger-codegen version

3.0.19

Swagger declaration file content or url

openapi: 3.0.1
info:
  title: Inheritance
  description: A description
  contact:
    email: me@example.com
  version: 0.0.0
paths:
  /pets:
    patch:
      requestBody:
        content:
          application/json:
            schema:
              oneOf:
                - $ref: '#/components/schemas/Cat'
                - $ref: '#/components/schemas/Dog'
              discriminator:
                propertyName: petType
      responses:
        '200':
          description: Updated
components:
  schemas:
    Pet:
      type: object
      required:
        - petType
      properties:
        petType:
          type: string
      discriminator: 
        propertyName: petType
    Dog:     # "Dog" is a value for the pet_type property (the discriminator value)
      allOf: # Combines the main `Pet` schema with `Dog`-specific properties 
        - $ref: '#/components/schemas/Pet'
        - type: object
          # all other properties specific to a `Dog`
          properties:
            bark:
              type: boolean
            breed:
              type: string
              enum: [Dingo, Husky, Retriever, Shepherd]
    Cat:     # "Cat" is a value for the pet_type property (the discriminator value)
      allOf: # Combines the main `Pet` schema with `Cat`-specific properties 
        - $ref: '#/components/schemas/Pet'
        - type: object
          # all other properties specific to a `Cat`
          properties:
            hunts:
              type: boolean
            age:
              type: integer

The command line:

$ java -jar swagger-codegen-cli.jar generate \
-i inheritance.yaml \
-l java \
-o java

Generates this in JSON:

GsonFireBuilder fireBuilder = new GsonFireBuilder()
  .registerTypeSelector(Pet.class, new TypeSelector<Pet>() {
    @Override
    public Class<? extends Pet> getClassForElement(JsonElement readElement) {
        Map<String, Class<? extends Pet>> classByDiscriminatorValue = new HashMap<>();
            classByDiscriminatorValue.put("Cat".toUpperCase(), Cat.class);
            classByDiscriminatorValue.put("Dog".toUpperCase(), Dog.class);
            classByDiscriminatorValue.put("Pet".toUpperCase(), Pet.class);
        return getClassByDiscriminator(
                    classByDiscriminatorValue,
                    getDiscriminatorValue(readElement, ""));
    }
  })

Note the empty "" where the discriminator value (petType) should be.

When I try to deserialize:

java.lang.IllegalArgumentException: missing discriminator field: <>
	at io.swagger.client.JSON.getDiscriminatorValue(JSON.java:124)
	at io.swagger.client.JSON.access$0(JSON.java:121)
	at io.swagger.client.JSON$1.getClassForElement(JSON.java:62)
	at io.gsonfire.gson.TypeSelectorTypeAdapterFactory$TypeSelectorTypeAdapter.read(TypeSelectorTypeAdapterFactory.java:65)
	at io.gsonfire.gson.NullableTypeAdapter.read(NullableTypeAdapter.java:36)
	at io.gsonfire.gson.HooksTypeAdapter.deserialize(HooksTypeAdapter.java:86)
	at io.gsonfire.gson.HooksTypeAdapter.read(HooksTypeAdapter.java:54)
	at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.read(TypeAdapterRuntimeTypeWrapper.java:41)
	at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:82)
	at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.read(CollectionTypeAdapterFactory.java:61)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222)
	at com.google.gson.Gson.fromJson(Gson.java:932)
	at com.google.gson.Gson.fromJson(Gson.java:870)

When I generate using OpenAPI Generator::4.3.0:

GsonFireBuilder fireBuilder = new GsonFireBuilder()
        .registerTypeSelector(Pet.class, new TypeSelector() {
            @Override
            public Class getClassForElement(JsonElement readElement) {
                Map classByDiscriminatorValue = new HashMap();
                classByDiscriminatorValue.put("Dog".toUpperCase(Locale.ROOT), Dog.class);
                classByDiscriminatorValue.put("Cat".toUpperCase(Locale.ROOT), Cat.class);
                classByDiscriminatorValue.put("Pet".toUpperCase(Locale.ROOT), Pet.class);
                return getClassByDiscriminator(classByDiscriminatorValue,
                        getDiscriminatorValue(readElement, "petType"));
            }
  })
;

(petType is populated here).

Command line used for generation

Using the Gradle plugin, config as above.

Steps to reproduce

gradle generateSwaggerCodeInheritance

[Yingsheng-eroad]

Using OpenAPI tools, I have an issue, if I choose an enum as the discriminator.
incompatible types: String cannot be converted to DeviceType

[mdashti]

i encountered the exact same issue and took me a while to figure out it's not a misspelling on my side! Would really apprecite if you could fix this issue.

[dordal]

This is more than just Java; I've seen it in PHP and Python ( see #10168 ), and I believe it may be an issue in all languages.

[mgazim]

Are there any plans to fix this? Experiencing the same issue on swagger-codegen 3.0.24 with Java. I'm not an expert in this so any workarounds are appreciated :)

[rhvonlehe]

I'm seeing the same thing with Swagger-codegen 2.4.18. This is the 2nd bug I've encountered, the first being code that was generated was invalid - invalid methods were being called against an imported library.

Actually what I am seeing is a bit different. I have polymorphism using 'allOf' instead of 'oneOf', so I only ever have 1 leaf class from any base class. In my case I was able to just delete the code it was generating to deal with discriminators since it made no sense. The types were already being determined just fine.

[dawnstrider]

Bug reproducable with following API spec:
https://developer.atlassian.com/cloud/jira/platform/swagger.v3.json
and swagger codegen:
3.0.25

[alexnb]

This seems to be fixed with 3.0.27

[dawnstrider]

Still reproducible with the swagger json from Atlassian and codegen 3.0.35

[jonmartinsolaas]

Seems to work with openapi-generator. At least for my little hello-world-test.

java -jar openapi-generator-cli.jar generate -i https://developer.atlassian.com/cloud/jira/platform/swagger-v3.v3.json -g java -o ./jira-client