Peewee：通过多对多关系过滤

Question

以下是一个基本示例 - 帖子归用户所有并且很受用户欢迎。如何为特定用户选择喜欢的帖子？

import datetime 
import peewee 

class User(peewee.Model): 
    name = peewee.CharField(max_length=200) 

class Post(peewee.Model): 
    user = peewee.ForeignKeyField(User) 
    text = peewee.TextField() 

class Like(peewee.Model): 
    user = peewee.ForeignKeyField(User) 
    post = peewee.ForeignKeyField(Post) 
    time = peewee.DateTimeField(default=datetime.datetime.now) 

我做一个查询从象模型的角度来看，用Like.select()开始查询，并加入Post模型。可以吗？我如何从Post模型的角度来查询，即Post.select()...？

这里有一个舒适的完整示例：

def check_likes(): 
    user, _ = User.get_or_create(name="John") 
    post, _ = Post.get_or_create(text="Hello world!", user=user) 
    like, _ = Like.get_or_create(post=post, user=user) 

    print("Created: ", user, post, like) 

    # Get liked posts for user 
    query_likes = (Like.select() 
     .where(Like.user == user) 
     .join(User) 
     .join(Post)) 
    liked_posts = [like.post for like in query_likes] 

    print("Liked posts: ", liked_posts) 

if __name__ == '__main__': 
    User.create_table(True) 
    Post.create_table(True) 
    Like.create_table(True) 

    check_likes() 

UPD。我结束了这样的查询的时刻：

def liked_by(user_id): 
    """Active posts liked by user.""" 
    return (Post.select(Post, User, Like) 
     .join(User, on=(Post.user == User.id)) 
     .switch(Post) 
     .join(Like, peewee.JOIN.LEFT_OUTER, 
       on=(Like.post == Post.id).alias('like')) 
     .where(Like.user == user_id) 
     .order_by(Like.time.desc())) 

Answer 1

上述查询应该工作，但你可能改一改：

Like.select(Like, Post)... 

您还需要考虑你是如何加入照顾表。使用 '开关' 的方法：

query_likes = (Like.select(Like, Post) # <<< Add like and post 
    .where(Like.user == user) 
    .join(User) 
    .switch(Like) # <<< You need this. 
    .join(Post)) 
liked_posts = [like.post for like in query_likes] 

你也可以这样做：

Post.select().join(Like).where(Like.user == some_user)