Fetch posts from non blocking users

问题

I'm trying to fetch some posts from users that isn't blocking "me". Se models below:

User
  id
  username
  ....

Post
  id
  user_id
  content
  ...

Blockings
  blocker_id
  blocked_id

I need to fetch posts from all users that isn't blocking me.

I fetch all posts with:

@posts Post.all

But how do I joins this together.

Pseudo

SELECT * FROM posts WHERE "posts.user_id isn't blocking me"

I have a helper called current_user that returns the current logged in user "me".

回答1:

A way to do it with SQL would be:

select *
  from post
  where user_id not in 
    (select blocker_id 
    from blockings
    where blocked_id = 1);

Just replace the numerical id with the variable.

SQL Fiddle

回答2:

In your Post class and a scope like this :

scope :not_blocked_from, lambda{|user| where("blocked_id <> ?", user.id)}

And you can fetch those posts you want as below:

Post.not_blocked_from(me)

Will work.

来源：https://stackoverflow.com/questions/13155462/fetch-posts-from-non-blocking-users