[java] Compilation failure when 'discriminator' is introduced

Description

I got the following error when generate code by using openapi-generator-maven-plugin.

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project swagger-vnfm: Compilation failure
[ERROR] /swagger-vnfm/target/generated-sources/src/main/java/com/openapi/test/VimConnectionInfo.java:[43,49] incompatible types: java.lang.String cannot be converted to com.openapi.test.VimType

openapi-generator version

<version>3.2.0</version>

OpenAPI declaration file content or url

swagger: '2.0'
info:
  description: This spec is mainly for testing
  version: 1.0.0
  title: Swagger Petstore
  termsOfService: 'http://swagger.io/terms/'
  contact:
    email: [e-mail]
  license:
    name: Apache-2.0
    url: 'http://www.apache.org/licenses/LICENSE-2.0.html'
host: 'petstore.swagger.io:80'
basePath: /v2
paths:
  /test:
    get:
      description: Gets all operation occurrence resources.
      responses:
        '200':
          description: Successful response
          schema:
            type: string
        default:
          description: Error payload
          schema:
            type: string
      tags:
        - test
schemes:
  - http
definitions:
  VimType:
    description: Type of the VIM info structure.
    type: string
    enum:
      - OPENSTACK_V2
      - OPENSTACK_V3
      - VMWARE_VCLOUD
      - OTHER_VIM_INFO
  VimConnectionInfo:
    type: object
    required:
      - id
      - vimType
    discriminator: vimType
    properties:
      id:
        description: Identifier of the VIM
        type: string
      vimType:
        $ref: '#/definitions/VimType'
externalDocs:
  description: Find out more about Swagger
  url: 'http://swagger.io'

Command line used for generation

mvn clean compile

Steps to reproduce

The maven pom.xml is

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.vnfm.model</groupId>
    <artifactId>swagger-vnfm</artifactId>
    <packaging>jar</packaging>
    <version>DYNAMIC-SNAPSHOT</version>
    <name>swagger-vnfm</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <dependency>
            <groupId>io.swagger</groupId>
            <artifactId>swagger-annotations</artifactId>
            <version>${swagger-core-version}</version>
        </dependency>
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>${gson-version}</version>
        </dependency>
    </dependencies>
    <properties>
        <java.version>1.8</java.version>
        <maven.compiler.source>${java.version}</maven.compiler.source>
        <maven.compiler.target>${java.version}</maven.compiler.target>
        <swagger-core-version>1.5.21</swagger-core-version>
        <gson-version>2.8.1</gson-version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <build>
        <plugins>
            <plugin>
                <groupId>org.openapitools</groupId>
                <artifactId>openapi-generator-maven-plugin</artifactId>
                <version>3.2.0</version>
                <executions>
                    <execution>
                        <id>lcm-generate</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                        <configuration>
                            <inputSpec>${project.basedir}/src/main/resources/swagger.yaml</inputSpec>
                            <language>java</language>
                            <generateApis>false</generateApis>
                            <generateModelTests>false</generateModelTests>
                            <generateModelDocumentation>false</generateModelDocumentation>
                            <generateSupportingFiles>false</generateSupportingFiles>
                            <skipOverwrite>true</skipOverwrite>
                            <configOptions>
                                <dateLibrary>java8</dateLibrary>
                            </configOptions>
                            <output>${project.build.directory}/generated-sources</output>
                            <modelPackage>com.openapi.test</modelPackage>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Related issues/PRs

No

Suggest a fix/enhancement

[antweb]

Using an enum descriminator is still broken on 4.2.3 and the current master (4.3.0-SNAPSHOT).

I built a simple example based on the OpenAPI docs:

components:
  schemas:
    Pet:
      oneOf:
        - $ref: "#/components/schemas/Cat"
        - $ref: "#/components/schemas/Dog"
        - $ref: "#/components/schemas/Lizard"
      discriminator:
        propertyName: petType
        mapping:
          Cat: "#/components/schemas/Cat"
          Dog: "#/components/schemas/Dog"
          Lizard: "#/components/schemas/Lizard"

    Cat:
      type: object
      properties:
        petType:
          $ref: "#/components/schemas/PetType"
        name:
          type: string

    Dog:
      type: object
      properties:
        petType:
          $ref: "#/components/schemas/PetType"
        bark:
          type: string

    Lizard:
      type: object
      properties:
        petType:
          $ref: "#/components/schemas/PetType"
        lovesRocks:
          type: boolean

    PetType:
      type: string
      enum:
        - Cat
        - Dog
        - Lizard

Generated with

java -jar openapi-generator-cli.jar generate \
  -i api.yaml \
  --api-package 'com.test.api' \
  --model-package 'com.test.model' \
  -g java \
  --library 'retrofit2' \
  -o generated/

The issue seems to be this line in the constructor of the base type (Pet):

this.petType = this.getClass().getSimpleName();

which doesn’t compile unless petType is a String. The fix should be rather simple. Whenever the discriminator is an enum, the constructor should be something like this:

this.petType = PetType.fromValue(this.getClass().getSimpleName());

[RevealOscar]

Same here as well