[QUESTION] Different attribute names in ORM and Pydantic models?

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Description

Hello! I am building an API using FastAPI and would like to have different attribute names across my ORM models and public user-facing resources. For example, here is my ORM User model:

class UserOrm(Base):
    id = Column(Integer, primary_key=True)
    name = Column(String)

and here is my corresponding Pydantic user model:

class UserResource(BaseModel):
    identifier: int
    fullname: str

In the public API, I’d like to accept a UserResource object where the attributes are named identifier and fullname. But internally I need some glue that tells FastAPI that identifier on UserResource maps to id on UserOrm. Is this possible?

I’ve explored doing this differently by defining my UserResource with an alias on Field like this:

class UserResource(BaseModel):
    id: int = Field(alias="identifier")
    name: str = Field(alias="fullname")

This lets me accept POST requests from clients where the attributes are named identifier and fullname, and my UserResource request model gets correctly populated, ie id and name have the values I’d expect. However when sending an updated UserResource back to the client, the automatic translation from UserOrm’s attribute names to the expected aliased attribute names on UserResource does not happen.

[fribor]

Hi,

the alias parameter defines the public name for the pydantic model. What happens, is that pydantic treats your field name as a private name as soon as you are using an alias. You can change that behavior by setting allow_population_by_field_name = True . Your pydantic schema should look like this:

class UserResource(BaseModel):
    id: int = Field(alias="identifier")
    name: str = Field(alias="fullname")

    class Config:
        allow_population_by_field_name = True

Here is the relevant part of the manual: Docs

[AIJIJI]

Even when I set allow_population_by_field_name = True. The response still return dict by alias. Example:

class RecordOut(BaseModel):
    id: str = Field(alias="_id")

    class Config:
        allow_population_by_field_name = True


@app.get("/record", response_model=RecordOut)
def read_record():
    record = {"_id": "123"}
    assert "id" in RecordOut(**record).dict(by_alias=False)
    return RecordOut(**record).dict(by_alias=False)
   # Response still has "_id" field!!!!

Am I doing something wrong?

OK, I find the solution: just add a param response_model_by_alias=False to the decorator.