Do not instantiate intermediate AR objects when eager loading.

Closes #3313

activerecord/CHANGELOG.md

@@ -1,5 +1,11 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Do not instantiate intermediate Active Record objects when eager loading.
+    These records caused `after_find` to run more than expected.
+    Fix #3313
+
+    *Yves Senn*
+
 *   Add STI support to init and building associations.
     Allows you to do BaseClass.new(:type => "SubClass") as well as
     parent.children.build(:type => "SubClass") or parent.build_child

activerecord/lib/active_record/relation/finder_methods.rb

@@ -225,9 +225,11 @@ module ActiveRecord
       orders = relation.order_values.map { |val| val.presence }.compact
       values = @klass.connection.distinct("#{quoted_table_name}.#{primary_key}", orders)
 
-      relation = relation.dup
+      relation = relation.dup.select(values)
+
+      id_rows = @klass.connection.select_all(relation.arel, 'SQL', relation.bind_values)
+      ids_array = id_rows.map {|row| row[primary_key]}
 
-      ids_array = relation.select(values).collect {|row| row[primary_key]}
       ids_array.empty? ? raise(ThrowResult) : table[primary_key].in(ids_array)
     end
 

activerecord/test/cases/associations/eager_test.rb

@@ -944,6 +944,12 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_equal 3, Developer.all.merge!(:includes => 'projects', :where => { 'developers_projects.access_level' => 1 }, :limit => 5).to_a.size
   end
 
+  def test_dont_create_temporary_active_record_instances
+    Developer.instance_count = 0
+    developers = Developer.all.merge!(:includes => 'projects', :where => { 'developers_projects.access_level' => 1 }, :limit => 5).to_a
+    assert_equal developers.count, Developer.instance_count
+  end
+
   def test_order_on_join_table_with_include_and_limit
     assert_equal 5, Developer.all.merge!(:includes => 'projects', :order => 'developers_projects.joined_on DESC', :limit => 5).to_a.size
   end

activerecord/test/models/developer.rb

@@ -57,6 +57,16 @@ class Developer < ActiveRecord::Base
   def log=(message)
     audit_logs.build :message => message
   end
+
+  after_find :track_instance_count
+  cattr_accessor :instance_count
+
+  def track_instance_count
+    self.class.instance_count ||= 0
+    self.class.instance_count += 1
+  end
+  private :track_instance_count
+
 end
 
 class AuditLog < ActiveRecord::Base