SQLAlchemy 如何在多对多中按子项过滤 [英] SQLAlchemy how to filter by children in many to many

问题描述

我问了一个我在 SQLAlchemy 中遇到的问题，并在写作时找到了解决方案.无论如何我都会发布它以防万一它对某人有帮助:)

I was asking for a problem I had in SQLAlchemy and found the solution while writing. I post it anyway just in case it helps somebody :)

假设我有一个似乎有效的多对多关系(至少我可以获取孩子)三个表:posts、tags 和 post_tags.

Let's say I have a many to many relationship that seems to work (at least I can fetch children) Three tables: posts, tags and 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在 Post 中首先按 date_out 过滤.我可以这样:

Now my problem is that I want to filter first by date_out in Post. I can get it like this:

# assume start_date and end_date

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

但如何同时按标签过滤?

But how to filter by tags at the same time?

推荐答案

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:这是我实际代码的极简示例，我可能在简化时犯了一个错误.

Disclaimer: this is a veeery reduced example of my actual code, I might have made a mistake while simplifying.

希望对大家有所帮助.

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