[BUG][PYTHON] SDK generating on `anyOf` is not supported within items

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?

Description

anyOf seems to be broken for the cases from the description:

components:
  schemas:
    CreateItemRequest:
      type: object
      required:
        - items
      properties:
        items:
          type: array
          items:
            $ref: '#/components/schemas/CreateItem'
    CreateItem:
      anyOf:
        - $ref: '#/components/schemas/CreateItemA'
        - $ref: '#/components/schemas/CreateItemB'
      discriminator:
        propertyName: type
        mapping:
          a: '#/components/schemas/CreateItemA'
          b: '#/components/schemas/CreateItemB'
    CreateItemA:
      type: object
      title: Create Item A
      properties:
        type:
          type: string
          default: a
        a:
          type: string
      required:
        - type
    CreateItemB:
      type: object
      title: Create Item B
      properties:
        type:
          type: string
          default: b
        b:
          type: string
      required:
        - type
        - b

Correct me if it is a BUG or if I am using the generated SDK in a wrong way.

request = CreateItemRequest(recipients=[CreateItem(type="a"), CreateItem(type="b", b="b")])

• Expected result for CreateItemRequest should be like:

request.recipients[0].model_dump()
# {"type": "a"}
request.recipients[1].model_dump()
# {"type": "b", "b": "b"}

• Actual result for CreateItemRequest:

request.recipients[0].model_dump()
{'anyof_schema_1_validator': None, 'anyof_schema_2_validator': None, 'actual_instance': None, 'any_of_schemas': {'CreateItemA', 'CreateItemB'}, 'discriminator_value_class_map': {}}
request.recipients[1].model_dump()
{'anyof_schema_1_validator': None, 'anyof_schema_2_validator': None, 'actual_instance': None, 'any_of_schemas': {'CreateItemA', 'CreateItemB'}, 'discriminator_value_class_map': {}}

openapi-generator version

v7.16.0

OpenAPI declaration file content

openapi: 3.0.3
info:
  title: Public API
  version: 1.0.0
paths:
  /path:
    post:
      summary: Create
      operationId: createItems
      description: Create items
      requestBody:
        required: true
        content:
          application/json:
            schema:
                $ref: '#/components/schemas/CreateItemRequest'
      responses:
        '200':
          description: OK
components:
  schemas:
    CreateItemRequest:
      type: object
      required:
        - items
      properties:
        items:
          type: array
          items:
            $ref: '#/components/schemas/CreateItem'
    CreateItem:
      anyOf:
        - $ref: '#/components/schemas/CreateItemA'
        - $ref: '#/components/schemas/CreateItemB'
      discriminator:
        propertyName: type
        mapping:
          a: '#/components/schemas/CreateItemA'
          b: '#/components/schemas/CreateItemB'
    CreateItemA:
      type: object
      title: Create Item A
      properties:
        type:
          type: string
          default: a
        a:
          type: string
      required:
        - type
    CreateItemB:
      type: object
      title: Create Item B
      properties:
        type:
          type: string
          default: b
        b:
          type: string
      required:
        - type
        - b

Generation Details

# config.yaml
gitRepoId: 'api-python-client'
gitUserId: 'Test'
packageName: 'test_client'
httpUserAgent: 'test_client/1.0.0'
additionalProperties:
  packageVersion: '1.0.0'
  projectName: 'test-client'
  infoName: 'test'

Steps to reproduce

docker run --rm -v "${PWD}:/local" openapitools/openapi-generator-cli:v7.16.0 generate -i /local/openapi.yaml -g python -o /local/test_client

Results in:

# test_client/api/default_api.py
...
class DefaultApi:
...
    @validate_call
    def create_items(
        self,
        create_item_request: CreateItemRequest,
        _request_timeout: Union[
...

# test_client/models/create_item_request.py
class CreateItemRequest(BaseModel):
    """
    CreateItemRequest
    """ # noqa: E501
    items: List[CreateItem]
    __properties: ClassVar[List[str]] = ["items"]

This part requires energy to dive into

# test_client/models/create_item.py
CREATEITEM_ANY_OF_SCHEMAS = ["CreateItemA", "CreateItemB"]

class CreateItem(BaseModel):
    """
    CreateItem
    """

    # data type: CreateItemA
    anyof_schema_1_validator: Optional[CreateItemA] = None
    # data type: CreateItemB
    anyof_schema_2_validator: Optional[CreateItemB] = None
    if TYPE_CHECKING:
        actual_instance: Optional[Union[CreateItemA, CreateItemB]] = None
    else:
        actual_instance: Any = None
    any_of_schemas: Set[str] = { "CreateItemA", "CreateItemB" }

    model_config = {
        "validate_assignment": True,
        "protected_namespaces": (),
    }

    discriminator_value_class_map: Dict[str, str] = {
    }

    def __init__(self, *args, **kwargs) -> None:
        if args:
            if len(args) > 1:
                raise ValueError("If a position argument is used, only 1 is allowed to set `actual_instance`")
            if kwargs:
                raise ValueError("If a position argument is used, keyword arguments cannot be used.")
            super().__init__(actual_instance=args[0])
        else:
            super().__init__(**kwargs)

    @field_validator('actual_instance')
    def actual_instance_must_validate_anyof(cls, v):
        instance = CreateItem.model_construct()
        error_messages = []
        # validate data type: CreateItemA
        if not isinstance(v, CreateItemA):
            error_messages.append(f"Error! Input type `{type(v)}` is not `CreateItemA`")
        else:
            return v

        # validate data type: CreateItemB
        if not isinstance(v, CreateItemB):
            error_messages.append(f"Error! Input type `{type(v)}` is not `CreateItemB`")
        else:
            return v

        if error_messages:
            # no match
            raise ValueError("No match found when setting the actual_instance in CreateItem with anyOf schemas: CreateItemA, CreateItemB. Details: " + ", ".join(error_messages))
        else:
            return v

    @classmethod
    def from_dict(cls, obj: Dict[str, Any]) -> Self:
        return cls.from_json(json.dumps(obj))

    @classmethod
    def from_json(cls, json_str: str) -> Self:
        """Returns the object represented by the json string"""
        instance = cls.model_construct()
        error_messages = []
        # anyof_schema_1_validator: Optional[CreateItemA] = None
        try:
            instance.actual_instance = CreateItemA.from_json(json_str)
            return instance
        except (ValidationError, ValueError) as e:
             error_messages.append(str(e))
        # anyof_schema_2_validator: Optional[CreateItemB] = None
        try:
            instance.actual_instance = CreateItemB.from_json(json_str)
            return instance
        except (ValidationError, ValueError) as e:
             error_messages.append(str(e))

        if error_messages:
            # no match
            raise ValueError("No match found when deserializing the JSON string into CreateItem with anyOf schemas: CreateItemA, CreateItemB. Details: " + ", ".join(error_messages))
        else:
            return instance

    def to_json(self) -> str:
        """Returns the JSON representation of the actual instance"""
        if self.actual_instance is None:
            return "null"

        if hasattr(self.actual_instance, "to_json") and callable(self.actual_instance.to_json):
            return self.actual_instance.to_json()
        else:
            return json.dumps(self.actual_instance)

    def to_dict(self) -> Optional[Union[Dict[str, Any], CreateItemA, CreateItemB]]:
        """Returns the dict representation of the actual instance"""
        if self.actual_instance is None:
            return None

        if hasattr(self.actual_instance, "to_dict") and callable(self.actual_instance.to_dict):
            return self.actual_instance.to_dict()
        else:
            return self.actual_instance

    def to_str(self) -> str:
        """Returns the string representation of the actual instance"""
        return pprint.pformat(self.model_dump())

# test_client/models/create_item_a.py
class CreateItemA(BaseModel):
    """
    CreateItemA
    """ # noqa: E501
    type: StrictStr
    a: Optional[StrictStr] = None
    __properties: ClassVar[List[str]] = ["type", "a"]

# test_client/models/create_item_b.py
class CreateItemB(BaseModel):
    """
    CreateItemB
    """ # noqa: E501
    type: StrictStr
    b: StrictStr
    __properties: ClassVar[List[str]] = ["type", "b"]

Suggest a fix

Pydantic RootModel / Literal approach should be used instead

# test_client/models/create_item.py
class CreateItem(
    RootModel[Union[CreateItemA, CreateItemB]]
):
    root: Union[CreateItemA, CreateItemB] = Field(
        ..., discriminator="type"
    )

    def to_dict(self) -> Optional[Union[Dict[str, Any], CreateItemA, CreateItemB]]:
        """Returns the dict representation of the actual instance"""
        return self.model_dump()

# test_client/models/create_item_a.py
class CreateItemA(BaseModel):
    """
    CreateItemA
    """ # noqa: E501

    type: Literal["a"] = Field(..., examples=["a"])
    a: Optional[StrictStr] = None

# test_client/models/create_item_b.py
class CreateItemB(BaseModel):
    """
    CreateItemB
    """ # noqa: E501
    type: Literal["b"] = Field(..., examples=["b"])
    b: StrictStr

from test_client.models import CreateItemRequest, CreateItem


request = CreateItemRequest(items=[CreateItem(type="a"), CreateItem(type="b", b="b")])
request.items[0].model_dump()
# {'type': 'a', 'a': None}

request.items[1].model_dump()
# {'type': 'b', 'b': 'b'}

request = CreateItemRequest(items=[dict(type="a"), dict(type="b", b="b")])
request.items[0].model_dump()
# {'type': 'a', 'a': None}

>>> request.items[1].model_dump()
# {'type': 'b', 'b': 'b'}

===

Tested against local mock server [ fatapi, uvicorn ]:

# mock_server.py
from fastapi import FastAPI
import uvicorn


app = FastAPI(title="PandaDoc Mock API", version="1.0.0")


@app.post("/path")
async def path(payload: dict = None):
    assert payload == {'items': [{'type': 'a', 'a': None}, {'type': 'b', 'b': 'b'}]}
    print(f"\t ✅ {payload}")

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)

$ python mock_server.py
INFO:     Started server process [99687]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8000 (Press CTRL+C to quit)
         ✅ {'items': [{'type': 'a', 'a': None}, {'type': 'b', 'b': 'b'}]}
INFO:     127.0.0.1:53587 - "POST /path HTTP/1.1" 200 OK

import test_client
from test_client.models.create_item_request import CreateItemRequest, CreateItem

configuration = test_client.Configuration(
    host = "http://localhost:8000"
)


with test_client.ApiClient(configuration) as api_client:
    api_instance = test_client.DefaultApi(api_client)
    create_item_request = test_client.CreateItemRequest(items=[CreateItem(type="a"), CreateItem(type="b", b="b")]) 
    api_instance.create_items(create_item_request)
    
    # debug
    print(create_item_request.model_dump())

{'items': [{'type': 'a', 'a': None}, {'type': 'b', 'b': 'b'}]}

Reproduce the issue with the provided Docker generation command and OpenAPI declaration, then inspect the generated test_client/models/create_item.py and create_item_request.py files. Compare construction and model_dump behavior for the two anyOf variants with the expected outputs; done means array items validate and serialize as CreateItemA or CreateItemB rather than an empty wrapper.