SQLAlchemy

Question

在下面的 Todo 模型中，text 列有一个唯一约束。

如何缩小此约束以仅验证每个“外键”用户的唯一性，而不是像现在这样每个用户？

我使用 SQLite。

from sqlalchemy import Column, Integer, String, Boolean, ForeignKey
from sqlalchemy.orm import relationship

from database import Base

class Todo(Base):
    __tablename__ = 'todos'
    id = Column(Integer, primary_key=True, index=True)
    text = Column(String, unique=True)
    user_id = Column(Integer, ForeignKey('users.id'))

    user = relationship("User", back_populates="todos")

class User(Base):
    __tablename__  = 'users'
    id = Column(Integer, primary_key=True, index=True)
    username = Column(String, unique=True, index=True)
    hashed_password = Column(String)
    is_active = Column(Boolean, default=True)

    todos = relationship("Todo", back_populates="user")

Answer 1

如果你使用postgresql，你可以使用Partial Index来实现这个：

class Todo(Base):
    __tablename__ = 'todos'
    id = Column(Integer, primary_key=True, index=True)
    text = Column(String)  # ! removed the unique from here
    user_id = Column(Integer, ForeignKey('users.id'))

    user = relationship("User", back_populates="todos")

    # ! added unique index with 
    __table_args__ = (
        Index(
            "todo_text_uc",
            "text",
            unique=True,
            postgresql_where=(user_id != None),
            # postgresql_where=(~user_id.is_(None)),  # equivalent to the row above, but no linting warnings
        ),
    )

For sqlite just replace postgresql_where with sqlite_where.

SQLAlchemy - 如何使每个 ForeignKey 关系的列唯一？

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