Nullable and Non-nullable Columns in SQLAlchemy 2

Two basic ways to declare the nullable property of a table column in SQLAlchemy 2.0 ORM.

from sqlalchemy import Integer
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column


class Base(DeclarativeBase):
    ...


class Table(Base):
    __tablename__ = "table"

    id: Mapped[int] = mapped_column(primary_key=True)

    col_1: Mapped[int | None]
    col_2: Mapped[int]
    col_3 = mapped_column(Integer)
    col_4 = mapped_column(Integer, nullable=False)

The columns col_1 and col_2 are declared using only the Mapped type annotation. The columns col_3 and col_4 are declared using the mapped_column function.

col_1 and col_3 are nullable columns:

>>> Table.col_1.nullable
True
>>> Table.col_3.nullable
True

col_2 and col_4 are non-nullable columns:

>>> Table.col_2.nullable
False
>>> Table.col_4.nullable
False