Question

我有三个sqlalchemy表，如下所示。 Categories-feeds是一个多关系，feed-articles是一对多的关系。

我想要做的是通过查询Category对象来访问类别提要的文章。类似的东西：

Category.query.get(1).articles

如何使用以下代码？

category_feeds = db.Table('category_feeds',
    db.Column('feed_id', db.Integer, db.ForeignKey('feed.id')),
    db.Column('category_id', db.Integer, db.ForeignKey('category.id'))
)

class Article(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.Text)
    content = db.Column(db.Text)
    href = db.Column(db.Text)
    feed_id = db.Column(db.Integer, db.ForeignKey('feed.id'))

class Feed(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.Text)
    xml_url = db.Column(db.Text)
    html_url = db.Column(db.Text)
    articles = db.relationship('Article', backref='feed')

    def __init__(self, **kwargs):
        for key, value in kwargs.iteritems():
            setattr(self, key, value)

class Category(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.Text)
    feeds = db.relationship('Feed', secondary=category_feeds,
        backref=db.backref('categories'))
    articles = ???

    def __init__(self, **kwargs):
        for key, value in kwargs.iteritems():
            setattr(self, key, value)

Answer 1

您可以在Category类上添加一个属性，该属性将运行您需要的查询：

class Category(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.Text)
    feeds = db.relationship('Feed', secondary=category_feeds,
        backref=db.backref('categories'))

    @property
    def articles(self):
        this_category = Category.query.get(self.id)
        articles = db.session.query(Article).join(Article.feed).filter(Feed.categories.contains(this_category))
        return articles

    def __init__(self, **kwargs):
        for key, value in kwargs.iteritems():
            setattr(self, key, value)

有了这个，你可以简单地说：

articles = Category.get(1).articles
print [x.title for x in articles]

flask-sqlalchemy三通协会

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