From 6e56a03f834202af4e57c50a71cc74ea08303bfd Mon Sep 17 00:00:00 2001
From: lulalala <mark@goodlife.tw>
Date: Tue, 2 Oct 2012 22:30:06 +0800
Subject: Fix reset_counters() crashing on has_many :through associations. The
 counter column name in the intermediate model need to be access via the
 through reflection.

---
 activerecord/CHANGELOG.md                       |  5 +++++
 activerecord/lib/active_record/counter_cache.rb |  9 +++++++--
 activerecord/test/cases/counter_cache_test.rb   | 15 ++++++++++++++-
 activerecord/test/models/subscription.rb        |  2 +-
 activerecord/test/schema/schema.rb              |  1 +
 5 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 67bec5f38e..8ff4c4706c 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Fix `reset_counters` crashing on `has_many :through` associations.
+    Fix #7822.
+
+    *lulalala*
+
 *   Support for partial inserts.
 
     When inserting new records, only the fields which have been changed
diff --git a/activerecord/lib/active_record/counter_cache.rb b/activerecord/lib/active_record/counter_cache.rb
index c877079b25..d28cd560d9 100644
--- a/activerecord/lib/active_record/counter_cache.rb
+++ b/activerecord/lib/active_record/counter_cache.rb
@@ -22,8 +22,13 @@ module ActiveRecord
         counters.each do |association|
           has_many_association = reflect_on_association(association.to_sym)
 
-          foreign_key  = has_many_association.foreign_key.to_s
-          child_class  = has_many_association.klass
+          if has_many_association.is_a? ActiveRecord::Reflection::ThroughReflection
+            foreign_key  = has_many_association.through_reflection.foreign_key.to_s
+            child_class = has_many_association.through_reflection.klass
+          else
+            foreign_key  = has_many_association.foreign_key.to_s
+            child_class  = has_many_association.klass
+          end
           belongs_to   = child_class.reflect_on_all_associations(:belongs_to)
           reflection   = belongs_to.find { |e| e.foreign_key.to_s == foreign_key && e.options[:counter_cache].present? }
           counter_name = reflection.counter_cache_column
diff --git a/activerecord/test/cases/counter_cache_test.rb b/activerecord/test/cases/counter_cache_test.rb
index ee443741ca..fc46a249c8 100644
--- a/activerecord/test/cases/counter_cache_test.rb
+++ b/activerecord/test/cases/counter_cache_test.rb
@@ -10,9 +10,12 @@ require 'models/dog'
 require 'models/dog_lover'
 require 'models/person'
 require 'models/friendship'
+require 'models/subscriber'
+require 'models/subscription'
+require 'models/book'
 
 class CounterCacheTest < ActiveRecord::TestCase
-  fixtures :topics, :categories, :categorizations, :cars, :dogs, :dog_lovers, :people, :friendships
+  fixtures :topics, :categories, :categorizations, :cars, :dogs, :dog_lovers, :people, :friendships, :subscribers, :subscriptions, :books
 
   class ::SpecialTopic < ::Topic
     has_many :special_replies, :foreign_key => 'parent_id'
@@ -118,4 +121,14 @@ class CounterCacheTest < ActiveRecord::TestCase
       Person.reset_counters(michael.id, :followers)
     end
   end
+
+  test "reset counter of has_many :through association" do
+    subscriber = subscribers('second')
+    Subscriber.reset_counters(subscriber.id, 'books')
+    Subscriber.increment_counter('books_count', subscriber.id)
+
+    assert_difference 'subscriber.reload.books_count', -1 do
+      Subscriber.reset_counters(subscriber.id, 'books')
+    end
+  end
 end
diff --git a/activerecord/test/models/subscription.rb b/activerecord/test/models/subscription.rb
index 4bdb36ea46..bcac4738a3 100644
--- a/activerecord/test/models/subscription.rb
+++ b/activerecord/test/models/subscription.rb
@@ -1,4 +1,4 @@
 class Subscription < ActiveRecord::Base
-  belongs_to :subscriber
+  belongs_to :subscriber, :counter_cache => :books_count
   belongs_to :book
 end
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 798ea20efc..2e4ec96933 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -621,6 +621,7 @@ ActiveRecord::Schema.define do
   create_table :subscribers, :force => true, :id => false do |t|
     t.string :nick, :null => false
     t.string :name
+    t.column :books_count, :integer, :null => false, :default => 0
   end
   add_index :subscribers, :nick, :unique => true
 
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