favoritescontroller#destroy should work even if the post doesn't exist, remove from favorites on expunge (fixes #3222)

app/models/favorite.rb

@@ -5,15 +5,19 @@ class Favorite < ApplicationRecord
   attr_accessible :user_id, :post_id
 
   # this is necessary because there's no trigger for deleting favorites
-  def self.destroy_all(hash)
-    if hash[:user_id] && hash[:post_id]
-      connection.execute("delete from favorites_#{hash[:user_id] % 100} where user_id = #{hash[:user_id]} and post_id = #{hash[:post_id]}")
-    elsif hash[:user_id]
-      connection.execute("delete from favorites_#{hash[:user_id] % 100} where user_id = #{hash[:user_id]}")
+  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)
+  def self.add(post:, user:)
     Favorite.transaction do
       User.where(:id => user.id).select("id").lock("FOR UPDATE NOWAIT").first
 
@@ -27,17 +31,21 @@ class Favorite < ApplicationRecord
     end
   end
 
-  def self.remove(post, user)
+  def self.remove(user:, post: nil, post_id: nil)
     Favorite.transaction do
+      if post && post_id.nil?
+        post_id = post.id
+      end
+
       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)
-      Post.where(:id => post.id).update_all("fav_count = fav_count - 1")
-      post.delete_user_from_fav_string(user.id)
+      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)
+      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")
       user.favorite_count -= 1
-      post.fav_count -= 1
+      post.fav_count -= 1 if post
     end
   end
 end