Make sure count works on has_many :through associations using :group. Closes #10480 [remvee]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8742 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/lib/active_record/associations.rb

@@ -55,6 +55,12 @@ def initialize(owner, reflection)
     end
   end
 
+  class HasManyThroughCantCountOnColumnForGroupedAssociation < ActiveRecordError #:nodoc:
+    def initialize(owner, reflection, column_name)
+      super("Cannot count on column '#{column_name}' for association '#{owner.class.name}##{reflection.name}' grouped by '#{reflection.options[:group]}'.")
+    end
+  end
+
   class EagerLoadPolymorphicError < ActiveRecordError #:nodoc:
     def initialize(reflection)
       super("Can not eagerly load the polymorphic association #{reflection.name.inspect}")

activerecord/lib/active_record/associations/has_many_through_association.rb

@@ -124,6 +124,15 @@ def count(*args)
           column_name = "#{@reflection.quoted_table_name}.#{@reflection.klass.primary_key}" if column_name == :all
           options.merge!(:distinct => true) 
         end
+
+        if @reflection.options[:group]
+          unless column_name == :all
+            raise HasManyThroughCantCountOnColumnForGroupedAssociation.new(@owner, @reflection, column_name)
+          end
+          column_name = @reflection.options[:group]
+          options.merge!(:distinct => true)
+        end
+
         @reflection.klass.send(:with_scope, construct_scope) { @reflection.klass.count(column_name, options) } 
       end
 

activerecord/test/cases/associations/join_model_test.rb

@@ -603,6 +603,21 @@ def test_belongs_to_shared_parent
     end
   end
 
+  def test_group_has_many_through_should_use_group_for_count
+    using_length = authors(:david).reload.grouped_comments.length           # all associated comments are read first
+    using_count = authors(:david).reload.grouped_comments.count             # associated comments are only counted
+    assert_equal using_count, using_length
+
+    commented_posts = authors(:david).comments.map(&:post).uniq.size        # count commented posts manually
+    assert_equal commented_posts, authors(:david).grouped_comments.count
+  end
+
+  def test_group_has_many_through_should_not_allow_column_name_for_count
+    assert_raises ActiveRecord::HasManyThroughCantCountOnColumnForGroupedAssociation do
+      authors(:david).grouped_comments.count(:id)
+    end
+  end
+
   private
     # create dynamic Post models to allow different dependency options
     def find_post_with_dependency(post_id, association, association_name, dependency)

activerecord/test/models/author.rb

@@ -20,6 +20,7 @@ def testing_proxy_target
   has_many :funky_comments, :through => :posts, :source => :comments
   has_many :ordered_uniq_comments, :through => :posts, :source => :comments, :uniq => true, :order => 'comments.id'
   has_many :ordered_uniq_comments_desc, :through => :posts, :source => :comments, :uniq => true, :order => 'comments.id DESC'
+  has_many :grouped_comments, :through => :posts, :source => :comments, :group => 'comments.post_id'
 
   has_many :special_posts
   has_many :special_post_comments, :through => :special_posts, :source => :comments