[Java] Bug - Doesn't generate correct classes for models with same nested properties

[bcampolo]

Description

When an inline model has two or more properties that are inline objects (not using $ref) and those objects have the same set of properties the generator combines them in to a single Java class and references that class for both children properties even though these objects may not be conceptually related at all (see YAML example below)

openapi-generator version

5.0.1

OpenAPI declaration file content or url

components:
  schemas:
    Receipt:
      type: object
      properties:
        Order:
          type: object
          properties:
            id:
              type: integer
              format: int64
            name:
              type: string
        Customer:
          type: object
          properties:
            id:
              type: integer
              format: int64
            name:
              type: string

Command line used for generation

generate -i -g java --additional-properties=withXml=false,java8=true,library=native,serializationLibrary=jackson,dateLibrary=java8,hideGenerationTimestamp=true -o ./client

Steps to reproduce

Run generator using the above command line on a YAML file that includes the above snippet and you will get code that looks like this for Receipt:

public class Receipt {
  @SerializedName("Order")
  private ReceiptOrder order = null;

  @SerializedName("Customer")
  private ReceiptOrder customer = null;

Note both the "order" property and the "customer" property are of type ReceiptOrder which while functional seems wrong or at the very least confusing to anyone using the client, especially for methods with signatures like: setCustomer(ReceiptOrder customer)

Related issues/PRs

Not for openapi-generator but in swagger-codegen:
swagger-api/swagger-codegen#4883

Suggest a fix/enhancement

I would assume the default would not combine objects and would only combine objects when a $ref was used explicitly. At the very least an option should be provided to turn this combining logic off.

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[wing328]

As a workaround, add the title attribute to the inline schema or define these models separately and use $ref instead.

[wrightsonm]

@wing328 where should the title attribute be placed?
I am seeing the same issue (but title has already been specified)

"400": {
  "description": "Invalid request.",
  "schema": {
                            "title": "unqiueNamePost400Response",
                            "type": "object",
                            "properties": {
                                "submitTimeUtc": {

[rudrakshtripathi]

$ref for Separate Definitions
To prevent the generator from merging the two inline objects, you can define separate schemas for Order and Customer, and then use $ref to reference those schemas in your Receipt object.

Here's how you can modify your OpenAPI YAML -
components: schemas: Order: type: object properties: id: type: integer format: int64 name: type: string Customer: type: object properties: id: type: integer format: int64 name: type: string Receipt: type: object properties: Order: $ref: '#/components/schemas/Order' Customer: $ref: '#/components/schemas/Customer'
In this case, separate Java classes Order and Customer will be generated, and you won’t face the merging issue.