Multiple dtos for one entity and for different use cases

Question

This question is probably opinion based but since I don't master the libraries I prefer to ask. I'm working with SQLAlchemy FastAPI and Pydantic.

For a given entity, is it possible/good-practice to have multiple dtos ?

Let's put some context: We have a user table that contains these rows: email (PK), username, password, firstname, lastname.

We have the associated SQLAlchemy class:

class User(Base):
    __tablename__ = "user_account"

    email: Mapped[str] = mapped_column(String(60), primary_key=True)
    username: Mapped[str] = mapped_column(String(30))
    password: Mapped[str] = mapped_column(String(60))
    firstname: Mapped[str] = mapped_column(String(30))
    lastname: Mapped[str] = mapped_column(String(30))

    address= relationship("Address", cascade="all, delete-orphan", backref="user_account", lazy="joined")

As you can see we have a relationship with the Address table.

Laslty, we have the User DTO for pydantic

class UserDTO(BaseModel):
    email: str
    username: str
    password: str
    firstname: str
    lastname: str

The issue is simple. The first use case is a registration; using fastapi and pydantic we can get the json body as an isntance of the UserDTO class. Then SQLAlchemy does the insert without problem.

Now let's say I want to get a user with his Address data.

If I update my UserDTO this way:

class User(BaseModel):
    email: str
    username: str
    password: str
    firstname: str
    lastname: str

    address: list[something] | None = None

Then my registration service doesn't work because SQLAlchemy doesn't accept the extra "address" field.

So my question is: how do we use DTOs in this case? Do I need multiple UserDTO class for different use cases ? or is there another way to do this?