providing arel with column information when possible [#5392 state:resolved]

3 files changed, 29 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 4bf206d589..acfc5ccf14 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -2107,8 +2107,13 @@ module ActiveRecord
             def association_join
               return @join if @join
 
-              aliased_table = Arel::Table.new(table_name, :as => @aliased_table_name, :engine => arel_engine)
-              parent_table = Arel::Table.new(parent.table_name, :as => parent.aliased_table_name, :engine => arel_engine)
+              aliased_table = Arel::Table.new(table_name, :as      => @aliased_table_name,
+                                                          :engine  => arel_engine,
+                                                          :columns => klass.columns)
+
+              parent_table = Arel::Table.new(parent.table_name, :as      => parent.aliased_table_name,
+                                                                :engine  => arel_engine,
+                                                                :columns => parent.active_record.columns)
 
               @join = case reflection.macro
               when :has_and_belongs_to_many
@@ -2191,7 +2196,9 @@ module ActiveRecord
             end
 
             def relation
-              aliased = Arel::Table.new(table_name, :as => @aliased_table_name, :engine => arel_engine)
+              aliased = Arel::Table.new(table_name, :as => @aliased_table_name,
+                                                    :engine => arel_engine,
+                                                    :columns => klass.columns)
 
               if reflection.macro == :has_and_belongs_to_many
                 [Arel::Table.new(options[:join_table], :as => aliased_join_table_name, :engine => arel_engine), aliased]
diff --git a/activerecord/test/cases/associations/join_model_test.rb b/activerecord/test/cases/associations/join_model_test.rb
index b83966e91c..f131dc01f6 100644
--- a/activerecord/test/cases/associations/join_model_test.rb
+++ b/activerecord/test/cases/associations/join_model_test.rb
@@ -44,6 +44,16 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     assert !authors(:mary).unique_categorized_posts.loaded?
   end
 
+  def test_column_caching
+    # pre-heat our cache
+    Post.arel_table.columns
+    Comment.columns
+
+    Post.connection.column_calls = 0
+    2.times { Post.joins(:comments).to_a }
+    assert_equal 0, Post.connection.column_calls
+  end
+
   def test_has_many_uniq_through_find
     assert_equal 1, authors(:mary).unique_categorized_posts.find(:all).size
   end
diff --git a/activerecord/test/cases/helper.rb b/activerecord/test/cases/helper.rb
index 561bb22785..19a8a97c1a 100644
--- a/activerecord/test/cases/helper.rb
+++ b/activerecord/test/cases/helper.rb
@@ -57,6 +57,15 @@ ActiveRecord::Base.connection.class.class_eval do
   alias_method_chain :execute, :query_record
 end
 
+ActiveRecord::Base.connection.extend Module.new {
+  attr_accessor :column_calls
+  def columns(*args)
+    @column_calls += 1
+    super
+  end
+}
+ActiveRecord::Base.connection.column_calls = 0
+
 unless ENV['FIXTURE_DEBUG']
   module ActiveRecord::TestFixtures::ClassMethods
     def try_to_load_dependency_with_silence(*args)