fix PatchDict errors with inherited schemas #1324

[LeandroDeJesus-S]

Fixed the error that occurs when using PatchDict with a schema that inherits from other schemas #1324

Problematic Scenario

Consider the following schemas:

class SomeSchema(Schema):
    some_field: str

class OtherSchema(SomeSchema):
    other_field: str

When using these in a route, the method ninja.patch_dict.create_patch_schema relies solely on the __annotations__ attribute of the schema class. This means it only considers the annotations declared in the current schema, ignoring inherited fields. This leads to the following error:

@router.patch('/{uuid}', ...)
def endpoint(request, uuid: str, payload: PatchDict[OtherSchema]):
    ...
    
# Error:
# File ".../ninja/patch_dict.py", line 45, in __getitem__
#   new_cls = create_patch_schema(schema_cls)
#             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
# File ".../ninja/patch_dict.py", line 29, in create_patch_schema
#   t = schema_cls.__annotations__[f]
#       ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^
# KeyError: 'some_field'

Proposed Solution

To address this issue, I created a helper function that recursively collects annotations from all parent classes. It traverses the class hierarchy using the __base__ attribute until it reaches a base schema class (Schema, ModelSchema, or BaseModel), then merges all the collected __annotations__ in reverse order to preserve field overrides from the child class.

def get_schema_annotations(schema_cls: Type[Any]) -> Dict[str, Any]:
    schema = schema_cls
    schemas = []
    excluded_bases = (
        "<class 'ninja.schema.Schema'>",
        "<class 'ninja.orm.ModelSchema'>",
        "<class 'pydantic.main.BaseModel>",
    )
    while True:
        schemas.append(schema)
        schema = schema.__base__
        if str(schema) in excluded_bases:
            break

    annotations = {}
    for schema in reversed(schemas):
        annotations.update(schema.__annotations__)

    return annotations

[vitalik]

I think you can use actual classes here instead of their repr (which may break in some potential new version)

[LeandroDeJesus-S]

You are right, I have updated to use the classes instead of their repr.

[vitalik]

what you do here with while True you can do with class.__mro__
some thing like this:

def get_schema_annotations(schema_cls: Type[Any]) -> Dict[str, Any]:
    excluded_bases = {Schema, ModelSchema, BaseModel}
    annotations = {}

    for base in reversed(schema_cls.__mro__):
        if base in excluded_bases:
            break
        annotations.update(getattr(base, '__annotations__', {}))

    return annotations

[LeandroDeJesus-S]

This approach doesn’t work because when calling reversed(schema_cls.__mro__), it will always return an empty annotations dictionary. That’s because it will hit one of the excluded classes first:

class SomeSchema(Schema):
    name: str
    age: int
    category: Optional[str] = None

# reversed(SomeSchema.__mro__)
# [<class 'object'>, <class 'pydantic.main.BaseModel'>, <class 'ninja.schema.Schema'>, <class 'test_patch_dict.SomeSchema'>]

I updated to this solution:

def get_schema_annotations(schema_cls: Type[Any]) -> Dict[str, Any]:
    annotations: Dict[str, Any] = {}
    excluded_bases = {Schema, ModelSchema, BaseModel}
    bases = schema_cls.mro()[:-1]
    final_bases = reversed([b for b in bases if b not in excluded_bases])

    for base in final_bases:
        annotations.update(getattr(base, '__annotations__', {}))

    return annotations

[vitalik]

Thank you @LeandroDeJesus-S