python - SQLAlchemy 查询，加入关系并按计数排序

Question

我有两个 SQLAlchemy 模型设置如下:

##############
# Post Model #
##############
class Post(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    title = db.Column(db.String(250))
    content = db.Column(db.String(5000))
    timestamp = db.Column(db.Integer)
    author_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    likes = db.relationship('Like', backref = 'post', lazy = 'dynamic')

###############
# Likes Model #
###############
class Like(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    voter_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    post_id = db.Column(db.Integer, db.ForeignKey('post.id'))

如您所见，有一个帖子模型和一个用户喜欢这些帖子的模型。我想创建一个查询来选择所有帖子，按该帖子的喜欢数量排序。在 shell 中，我可以运行:

SELECT post.*, 
       count(like.id) AS num_likes
FROM post
LEFT JOIN like
ON post.id = like.post_id
GROUP BY post.id;

等效的 SQLAlchemy 命令是什么？

谢谢!

Answer 1

从原始查询到 Flask-SQLAlchemy 的转换非常机械:

db.session.query(Post, db.func.count(Like.id)).outerjoin(Like).group_by(Post.id)