improve relations and scopes

app/models/post.rb

@@ -7,6 +7,10 @@ class Post < ApplicationRecord
 
   validate :user, :limit_of_post_per_day
 
+  scope :by_user_follows, ->(user) {
+    where(user_id: user.following_ids)
+  }
+
   def repost?
     kind == :quoted_post
   end

app/models/user.rb

@@ -9,4 +9,9 @@ class User < ApplicationRecord
             }
 
   has_many :posts
+
+  has_many :user_follows_following, class_name: 'UserFollow', foreign_key: :follower_id
+  has_many :user_follows_followers, class_name: 'UserFollow', foreign_key: :followed_id
+  has_many :following, through: :user_follows_following, source: :followed
+  has_many :followers, through: :user_follows_followers, source: :follower
 end