expunge: decrement user favorite counts.

app/models/favorite.rb

@@ -4,19 +4,6 @@ class Favorite < ApplicationRecord
   scope :for_user, lambda {|user_id| where("user_id % 100 = #{user_id.to_i % 100} and user_id = #{user_id.to_i}")}
   attr_accessible :user_id, :post_id
 
-  # this is necessary because there's no trigger for deleting favorites
-  def self.destroy_all(user_id: nil, post_id: nil)
-    if user_id && post_id
-      connection.execute("delete from favorites_#{user_id % 100} where user_id = #{user_id} and post_id = #{post_id}")
-    elsif user_id
-      connection.execute("delete from favorites_#{user_id % 100} where user_id = #{user_id}")
-    elsif post_id
-      0.upto(99) do |uid|
-        connection.execute("delete from favorites_#{uid} where post_id = #{post_id}")
-      end
-    end
-  end
-
   def self.add(post:, user:)
     Favorite.transaction do
       User.where(:id => user.id).select("id").lock("FOR UPDATE NOWAIT").first
@@ -40,7 +27,7 @@ class Favorite < ApplicationRecord
       User.where(:id => user.id).select("id").lock("FOR UPDATE NOWAIT").first
 
       return unless Favorite.for_user(user.id).where(:user_id => user.id, :post_id => post_id).exists?
-      Favorite.destroy_all(user_id: user.id, post_id: post_id)
+      Favorite.for_user(user.id).delete_all(post_id: post_id)
       Post.where(:id => post_id).update_all("fav_count = fav_count - 1")
       post.delete_user_from_fav_string(user.id) if post
       User.where(:id => user.id).update_all("favorite_count = favorite_count - 1")

app/models/post.rb

@@ -1038,7 +1038,9 @@ class Post < ApplicationRecord
     end
 
     def remove_from_favorites
-      Favorite.destroy_all(post_id: self.id)
+      favorites.find_each do |fav|
+        remove_favorite!(fav.user)
+      end
     end
 
     def remove_from_fav_groups

test/unit/post_test.rb

@@ -80,6 +80,13 @@ class PostTest < ActiveSupport::TestCase
         end
       end
 
+      should "decrement the user's favorite count" do
+        @post.add_favorite!(@post.uploader)
+        assert_difference(["@post.uploader.reload.favorite_count"], -1) do
+          @post.expunge!
+        end
+      end
+
       should "remove the post from iqdb" do
         mock_iqdb_service!
         Post.iqdb_sqs_service.expects(:send_message).with("remove\n#{@post.id}")