[BUG] [python] AnyOf Parent class generates empty `from_dict` function.

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• 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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When generating models with the REF_AS_PARENT_IN_ALLOF normalizer option enabled, the parent model that is extended from will not have its from_dict() function generated correctly. It will be missing any function body, making it impossible for these models to be used in the API routes.

We would expect the parent from_dict function to also be implemented.

For example, When B inherits from A. A is generated as:

# coding: utf-8

"""
    My API

    No description provided (generated by Openapi Generator https://github.com/openapitools/openapi-generator)

    The version of the OpenAPI document: 1.0.0
    Generated by OpenAPI Generator (https://openapi-generator.tech)

    Do not edit the class manually.
"""  # noqa: E501


from __future__ import annotations
import pprint
import re  # noqa: F401
import json

from pydantic import BaseModel, ConfigDict, StrictStr
from typing import Any, ClassVar, Dict, List, Optional
from typing import Optional, Set
from typing_extensions import Self

class A(BaseModel):
    """
    A
    """ # noqa: E501
    a_field: Optional[StrictStr] = None
    __properties: ClassVar[List[str]] = ["a_field"]

    model_config = ConfigDict(
        populate_by_name=True,
        validate_assignment=True,
        protected_namespaces=(),
    )


    def to_str(self) -> str:
        """Returns the string representation of the model using alias"""
        return pprint.pformat(self.model_dump(by_alias=True))

    def to_json(self) -> str:
        """Returns the JSON representation of the model using alias"""
        # TODO: pydantic v2: use .model_dump_json(by_alias=True, exclude_unset=True) instead
        return json.dumps(self.to_dict())

    @classmethod
    def from_json(cls, json_str: str) -> Optional[Self]:
        """Create an instance of A from a JSON string"""
        return cls.from_dict(json.loads(json_str))

    def to_dict(self) -> Dict[str, Any]:
        """Return the dictionary representation of the model using alias.

        This has the following differences from calling pydantic's
        `self.model_dump(by_alias=True)`:

        * `None` is only added to the output dict for nullable fields that
          were set at model initialization. Other fields with value `None`
          are ignored.
        """
        excluded_fields: Set[str] = set([
        ])

        _dict = self.model_dump(
            by_alias=True,
            exclude=excluded_fields,
            exclude_none=True,
        )
        return _dict

    @classmethod
    def from_dict(cls, obj: Dict[str, Any]) -> Optional[Self]:
        """Create an instance of A from a dict"""

The generated model of B will have the correct from_dict function generated.

This issue also shows up with the python-pydantic-v1 generator.

openapi-generator version

7.9.0 & 7.10.0

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  title: My API
  version: 1.0.0

paths: {}

components:
  schemas:
    A:
      type: object
      properties:
        a_field:
          type: string

    B:
      allOf:
        - $ref: '#/components/schemas/A'
        - type: object
          properties:
            b_field:
              type: string

Generation Details

openapi-generator-cli generate -g python -i openapi.yaml --openapi-normalizer 'REFACTOR_ALLOF_WITH_PROPERTIES_ONLY=true,REF_AS_PARENT_IN_ALLOF=true'

Steps to reproduce

Related issues/PRs

Suggest a fix

Start by running the reported openapi-generator-cli command with the supplied OpenAPI declaration and compare the generated from_dict methods for models A and B. Trace the Python and python-pydantic-v1 generator paths, then verify that the parent model's from_dict has a working body in generated output for both generators.