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/
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