[BUG][KOTLIN] Polymorphism not working

[grassehh]

Bug Report Checklist

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

Description

Hi, I'm not certain is this is a bug or a feature since a few things seems to works correctly. When using polymorphism with discriminator exactly as documented on OpenAPI 3.0 specifications, the following of the generated code is incorrect:

• The parent interface contains all childs properties
• The child classes do not implement the parent interface
• The child classes do not have the override keyword on parent interface discriminator property

Note: The same issue is noticeable when using kotlin-spring generator

openapi-generator version

7.4.0

OpenAPI declaration file content or url

https://github.com/grassehh/openapi-generator-experiments/blob/main/openapi.yaml

Generation Details

Checkout this repository and build using gradle build. The generated code is in the build directory.

Steps to reproduce

Simply generate the Kotlin code as explained above then read the generated code in build directory.

Related issues/PRs

Suggest a fix

[mike-adonis]

@grassehh did you find a work around?.

[hagis]

I have used a workaround where I drop the "oneOf" from the parent and leave just the "discriminator". See the Pet, Cat, Dog, Lizard example at https://swagger.io/specification/v3/#discriminator-object

[grassehh]

I have used a workaround where I drop the "oneOf" from the parent and leave just the "discriminator". See the Pet, Cat, Dog, Lizard example at https://swagger.io/specification/v3/#discriminator-object

The problem I see with this workaround is that your specification is not compliant as the documentation states The discriminator object is legal only when using one of the composite keywords oneOf, anyOf, allOf

@mike-adonis currently our workaround is quite straightforward. We override dataClass.mustache and dataClassReqVar.mustache templates by setting the templateDir variable of the plugin in our gradle.kts file:

templateDir.set("$projectDir/docs/templates")

The drawback is that it requires us to rebase the templates everytime we bump the plugin version.

As of 7.8.0, here are our templates for the kotlin-spring plugin: dataclass.mustache:

/**
* {{{description}}}
{{#vars}}
    * @param {{name}} {{{description}}}
{{/vars}}
*/{{#discriminator}}
    {{>typeInfoAnnotation}}{{/discriminator}}
{{#additionalModelTypeAnnotations}}
    {{{.}}}
{{/additionalModelTypeAnnotations}}
{{#vendorExtensions.x-class-extra-annotation}}
    {{{.}}}
{{/vendorExtensions.x-class-extra-annotation}}
{{#discriminator}}interface {{classname}}{{/discriminator}}{{^discriminator}}{{#hasVars}}data {{/hasVars}}class {{classname}}(
{{#requiredVars}}
    {{>dataClassReqVar}}{{^-last}},
    {{/-last}}{{/requiredVars}}{{#hasRequired}}{{#hasOptional}},
{{/hasOptional}}{{/hasRequired}}{{#optionalVars}}{{>dataClassOptVar}}{{^-last}},
{{/-last}}{{/optionalVars}}
) {{/discriminator}}{{#vendorExtensions.x-implements}}{{#-first}}: {{{.}}}{{/-first}}{{^-first}}, {{{.}}}{{/-first}}{{/vendorExtensions.x-implements}}{
{{#discriminator}}{{#model.vendorExtensions.x-discriminator-type}}{{>modelMutable}} {{{discriminator.propertyName}}}: {{{model.vendorExtensions.x-discriminator-type}}}{{/model.vendorExtensions.x-discriminator-type}}{{/discriminator}}
{{#hasEnums}}{{#vars}}{{#isEnum}}
    /**
    * {{{description}}}
    * Values: {{#allowableValues}}{{#enumVars}}{{&name}}{{^-last}},{{/-last}}{{/enumVars}}{{/allowableValues}}
    */
    enum class {{{nameInPascalCase}}}(@get:JsonValue val value: {{#isContainer}}{{#items}}{{{dataType}}}{{/items}}{{/isContainer}}{{^isContainer}}{{{dataType}}}{{/isContainer}}) {
    {{#allowableValues}}{{#enumVars}}
        {{{name}}}({{{value}}}){{^-last}},{{/-last}}{{/enumVars}}{{/allowableValues}};

    companion object {
    @JvmStatic
    @JsonCreator
    fun forValue(value: {{#isContainer}}{{#items}}{{{dataType}}}{{/items}}{{/isContainer}}{{^isContainer}}{{{dataType}}}{{/isContainer}}): {{{nameInPascalCase}}} {
    return values().first{it -> it.value == value}
    }
    }
    }
{{/isEnum}}{{/vars}}{{/hasEnums}}
{{#serializableModel}}
    companion object {
    private const val serialVersionUID: kotlin.Long = 1
    }
{{/serializableModel}}
}

dataClassReqVar.mustache:

{{#useBeanValidation}}{{>beanValidation}}{{>beanValidationModel}}{{/useBeanValidation}}{{#swagger2AnnotationLibrary}}
    @Schema({{#example}}example = "{{#lambdaRemoveLineBreak}}{{#lambdaEscapeInNormalString}}{{{.}}}{{/lambdaEscapeInNormalString}}{{/lambdaRemoveLineBreak}}", {{/example}}required = true, {{#isReadOnly}}readOnly = {{{isReadOnly}}}, {{/isReadOnly}}description = "{{{description}}}"){{/swagger2AnnotationLibrary}}{{#swagger1AnnotationLibrary}}
    @ApiModelProperty({{#example}}example = "{{#lambdaRemoveLineBreak}}{{#lambdaEscapeInNormalString}}{{{.}}}{{/lambdaEscapeInNormalString}}{{/lambdaRemoveLineBreak}}", {{/example}}required = true, {{#isReadOnly}}readOnly = {{{isReadOnly}}}, {{/isReadOnly}}value = "{{{description}}}"){{/swagger1AnnotationLibrary}}{{#vendorExtensions.x-field-extra-annotation}}
    {{{.}}}{{/vendorExtensions.x-field-extra-annotation}}
@get:JsonProperty("{{{baseName}}}", required = true){{#vendorExtensions.x-overrides}} override{{/vendorExtensions.x-overrides}} {{>modelMutable}} {{{name}}}: {{#isEnum}}{{#isArray}}{{baseType}}<{{/isArray}}{{classname}}.{{{nameInPascalCase}}}{{#isArray}}>{{/isArray}}{{/isEnum}}{{^isEnum}}{{{dataType}}}{{/isEnum}}{{#isNullable}}?{{/isNullable}}{{#defaultValue}} = {{^isNumber}}{{{defaultValue}}}{{/isNumber}}{{#isNumber}}{{{dataType}}}("{{{defaultValue}}}"){{/isNumber}}{{/defaultValue}}

Then in the openapi.yaml:

1. We add x-overrides property in the definition of the properties which are overriden by the child classes. Example:

   type: string
   x-overrides: true
   description: my child property

2. We add x-implements property in the definition of each subclass. Example:

   type: object
   x-implements: [ "MyParentClass" ]
   description:  My child class
   properties:
   ...

[wing328]

            schema:
              title: Parent
              oneOf:
                - $ref: '#/components/schemas/child1'
                - $ref: '#/components/schemas/child2'
              discriminator:
                propertyName: discriminatorProperty
                mapping:
                  type1: 'child1'
                  type2: 'child2'

fyi. there's a new option called generateOneOfAnyOfWrappers for better oneOf/anyOf support: https://openapi-generator.tech/docs/generators/kotlin/

please give it a try to see if it better meet your requirement

[hagis]

The problem I see with this workaround is that your specification is not compliant as the documentation states The discriminator object is legal only when using one of the composite keywords oneOf, anyOf, allOf

The spec I linked is not mine, it is a sample from the actual OpenAPi 3 documentation.

And the linked spec uses allOf in the child classes meeting the legality constraint for the discriminator object.

[hagis]

fyi. there's a new option called generateOneOfAnyOfWrappers for better oneOf/anyOf support: https://openapi-generator.tech/docs/generators/kotlin/

please give it a try to see if it better meet your requirement

I tried that option beginning of June 2024 but the results were not usable. Have there been improvements on it since then?

[hagis]

fyi. there's a new option called generateOneOfAnyOfWrappers for better oneOf/anyOf support: https://openapi-generator.tech/docs/generators/kotlin/

please give it a try to see if it better meet your requirement

I just tried the generateOneOfAnyOfWrappers option but it generated uncompilable code. There are errors such as "Unresolved reference 'TypeAdapterFactory'".