I don't think this code was ever correct:
Base = DeclarativeBase()
Before SQLAlchemy 2.0, there was a declarative_base() function that was
used in the same way:
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
...but in SQLAlchemy 2.0, the preferred form is:
from sqlalchemy.orm import DeclarativeBase
class Base(DeclarativeBase):
pass
The new approach works better with type-analysis tools like mypy.
https://docs.sqlalchemy.org/en/20/changelog/whatsnew_20.html#whatsnew-20-orm-declarative-typing
Hope that helps,
Simon
On Tue, Oct 10, 2023 at 8:12 AM satya dev <satyadev0...@gmail.com> wrote:
> What is the difference between
> class Base(DeclarativeBase):
> pass
> vs
> Base = DeclarativeBase()
> I am following the SQLAlchemy Tutorial for declaring mapped classes
> <https://docs.sqlalchemy.org/en/20/tutorial/metadata.html> when I inherit
> the Base class I can access the metadata and create my tables but when I
> assign it to Base and try to create the tables it throws an error saying
> class User(Base):
> TypeError: DeclarativeBase() takes no arguments
>
>
> Code for reference:
> from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column,
> relationship
> from sqlalchemy import Integer, String, ForeignKey, MetaData, create_engine
> from typing import List, Optional
>
>
> engine = create_engine("postgresql://db_user:db_pw@localhost
> :5432/alembic_learning")
> # class Base(DeclarativeBase):
> # pass
>
> Base = DeclarativeBase()
>
> class User(Base):
> __tablename__ = "users"
>
> id: Mapped[int] = mapped_column(primary_key=True)
> name:Mapped[str] = mapped_column(String(30))
> fullname:Mapped[Optional[str]]
>
> addresses:Mapped[List["Address"]] = relationship(back_populates="user")
>
> def __repr__(self) -> str:
> return f"User(id={self.id!r}, name={self.name!r},
> fullname={self.fullname!r})"
> class Address(Base):
> __tablename__ = "address"
>
> id:Mapped[int] = mapped_column(primary_key=True)
> email_address:Mapped[str]
> user_id = mapped_column(ForeignKey("users.id"))
>
> user:Mapped[User] = relationship(back_populates="addresses")
>
> def __repr__(self)-> str:
> return f"Address(id={self.id!r}, email_address={self.email_address})"
>
> Base.metadata.create_all(bind=engine)
>
> --
> SQLAlchemy -
> The Python SQL Toolkit and Object Relational Mapper
>
> http://www.sqlalchemy.org/
>
> To post example code, please provide an MCVE: Minimal, Complete, and
> Verifiable Example. See http://stackoverflow.com/help/mcve for a full
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--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
Example. See http://stackoverflow.com/help/mcve for a full description.
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