SQLAlchemy如何在多对多中按孩子过滤

Posted 2023-03-16

【中文标题】SQLAlchemy如何在多对多中按孩子过滤

【英文标题】：SQLAlchemy how to filter by children in many to many

【发布时间】：2012-11-11 02:43:47

【问题描述】：

我在询问我在 SQLAlchemy 中遇到的问题，并在编写时找到了解决方案。无论如何我都会发布它以防万一它对某人有帮助:)

假设我有一个看起来有效的多对多关系（至少我可以获取孩子）三个表：posts、tags 和 post_tags。

import sqlalchemy as alc

class Tag(Base):
    __tablename__ = 'tags'

    id = alc.Column(alc.Integer, primary_key=True)
    name = alc.Column(alc.String)
    accepted = alc.Column(alc.Integer)

    posts = relationship('Post', secondary=post_tags)



class Post(Base):

    __tablename__ = 'posts'

    id = alc.Column(alc.Integer, primary_key=True)
    text = alc.Column(alc.String)
    date_out = alc.Column(alc.Date)

    tags = relationship('Mistake_Code', secondary=post_tags)

# relational table
post_tags = alc.Table('check_point_mistakes',
                       Base.metadata,
                       alc.Column('post_id', alc.Integer,ForeignKey('posts.id')),
                       alc.Column('tag_id', alc.Integer, alc.ForeignKey('tags.id')))

现在我的问题是我想先在 Post 中按 date_out 过滤。我可以这样得到：

# assume start_date and end_date

query = (
            session.query(Post)
                   .filter(Post.date_out.between(start_date, end_date))
 )

但是如何同时按标签过滤呢？

【参考方案1】：

query = (
    session.query(Post)
           .join(Post.tags)     # It's necessary to join the "children" of Post
           .filter(Post.date_out.between(start_date, end_date))
           # here comes the magic: 
           # you can filter with Tag, even though it was not directly joined)
           .filter(Tag.accepted == 1)
)

免责声明：这是我实际代码的一个非常简化的示例，我可能在简化时犯了一个错误。

我希望它对某人有所帮助。