SQLAlchemy 2.0 类型注解指南之Mapped与mapped_column详解

id = Column(Integer, primary_key=True)

from sqlalchemy import Column, Integer, String
class User(Base):
    __tablename__ = "user"
    id = Column(Integer, primary_key=True)
    name = Column(String(50), nullable=False)
    email = Column(String(100))

from sqlalchemy.orm import Mapped, mapped_column
from sqlalchemy import String
from typing import Optional
class User(Base):
    __tablename__ = "user"
    # Mapped[int] 告诉类型检查器：实例中的 id 是 int 类型
    # mapped_column(...) 定义了数据库列的属性
    id: Mapped[int] = mapped_column(primary_key=True)
    # nullable=False 是默认的，对应 Mapped[str]
    name: Mapped[str] = mapped_column(String(50))
    # Optional[str] 或 str | None 对应 nullable=True
    email: Mapped[Optional[str]] = mapped_column(String(100))

import uuid
from sqlalchemy.dialects.postgresql import UUID
from sqlalchemy import Column, DateTime, func
class Document(Base):
    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
    created_at = Column(DateTime(timezone=True), server_default=func.now())

import uuid
from datetime import datetime
from sqlalchemy.orm import Mapped, mapped_column
from sqlalchemy.dialects.postgresql import UUID
from sqlalchemy import DateTime, func
class Document(Base):
    # 明确指定 id 是 uuid.UUID 类型
    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
    # 明确指定 created_at 是 datetime 类型
    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())

from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship
class Post(Base):
    user_id = Column(Integer, ForeignKey("user.id"))
    user = relationship("User")

from sqlalchemy import ForeignKey
from sqlalchemy.orm import Mapped, mapped_column, relationship
class Post(Base):
    user_id: Mapped[int] = mapped_column(ForeignKey("user.id"))
    # 这里的 relationship 也支持 Mapped 类型
    user: Mapped["User"] = relationship()