fix(_sqlalchemy): type object SQLAlchemy.Base has no attribute 'model_fields'

[iYasha]

The problem

SqlalchemyCrud.on_update_pre uses model_fields function for both PyDantic.BaseModel and SQLAlchemy.Base, but the last has no attribute model_fields

Steps to reproduce

class CountryInDBSchema(BaseModel):
    id: UUID
    name: str
    deleted_at: Optional[datetime] = None

    class Config:
        orm_mode = True


class Country(Base):
    __tablename__ = "countries"
    __pydantic_model__ = CountryInDBSchema
    
    id = sa.Column(UUID, primary_key=True, index=True)
    name = sa.Column(sa.String, nullable=False)
    deleted_at = sa.Column(sa.DateTime(timezone=False), nullable=True, index=True)

1. Insert a new record to the countries table with deleted_at=null
2. Try to update this record in amis admin panel
3. Get error

  File "fastapi_amis_admin/crud/_sqlalchemy.py", line 575, in route
    values = await self.on_update_pre(request, data, item_id=item_id)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "fastapi_amis_admin/crud/_sqlalchemy.py", line 463, in on_update_pre
    data = {key: val for key, val in data.items() if val is not None or field_allow_none(model_fields(self.model)[key])}
                                                                                         ^^^^^^^^^^^^^^^^^^^^^^^^
  File "fastapi_amis_admin/utils/pydantic.py", line 86, in model_fields
    for field_name, field in model.model_fields.items():
                             ^^^^^^^^^^^^^^^^^^
AttributeError: type object 'Country' has no attribute 'model_fields'

How to fix

To fix this issue, we should check if self.model is SQLAlchemy model If so, then we should use __pydantic_model__ for model_fields, otherwise just pass self.model