使用两个外键定义关系的SQLAlchemy表

from sqlalchemy import Column, Integer, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    posts = relationship('Post', back_populates='user')

class Post(Base):
    __tablename__ = 'posts'
    id = Column(Integer, primary_key=True)
    title = Column(String)
    user_id = Column(Integer, ForeignKey('users.id'))
    user = relationship('User', back_populates='posts')
    category_id = Column(Integer, ForeignKey('categories.id'))
    category = relationship('Category', back_populates='posts')

class Category(Base):
    __tablename__ = 'categories'
    id = Column(Integer, primary_key=True)
    name = Column(String)
    posts = relationship('Post', back_populates='category')