From 65f055a3ed790d41aeca8d4ca7f3771b05cf544f Mon Sep 17 00:00:00 2001
From: Emilio Tagua <miloops@gmail.com>
Date: Mon, 5 Oct 2009 15:24:08 -0300
Subject: [PATCH] Added eager loading support to Relation and ActiveRecord#all.

---
 .../lib/active_record/associations.rb         |  4 +--
 activerecord/lib/active_record/base.rb        | 17 ++++------
 activerecord/lib/active_record/relation.rb    | 32 +++++++++++++++----
 .../cascaded_eager_loading_test.rb            |  2 +-
 4 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index b363cceccb..016745add2 100755
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1455,9 +1455,9 @@ module ActiveRecord
           after_destroy(method_name)
         end
 
-        def find_with_associations(options = {})
+        def find_with_associations(options = {}, join_dependency = nil)
           catch :invalid_query do
-            join_dependency = JoinDependency.new(self, merge_includes(scope(:find, :include), options[:include]), options[:joins])
+            join_dependency ||= JoinDependency.new(self, merge_includes(scope(:find, :include), options[:include]), options[:joins])
             rows = select_all_rows(options, join_dependency)
             return join_dependency.instantiate(rows)
           end
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index 2fd3384877..60e69f020c 100755
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -666,23 +666,18 @@ module ActiveRecord #:nodoc:
       def all(*args)
         options = args.extract_options!
 
-
         if options.empty? && !scoped?(:find)
           relation = arel_table
         else
+          relation = construct_finder_arel(options)
           include_associations = merge_includes(scope(:find, :include), options[:include])
 
-          # if include_associations.any? && references_eager_loaded_tables?(options)
-          #   join_dependency = JoinDependency.new(self, include_associations, options[:joins])
-
-          #   relation = construct_finder_arel_with_included_associations(options, join_dependency)
-
-          #   relation.preload(include_associations)
-          # else
-            relation = construct_finder_arel(options)
-            if include_associations.any?
+          if include_associations.any?
+            if references_eager_loaded_tables?(options)
+              relation.eager_load(include_associations)
+            else
               relation.preload(include_associations)
-            # end
+            end
           end
         end
         relation
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 6abb2df8ff..24fd29c7f3 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -7,11 +7,17 @@ module ActiveRecord
       @klass, @relation = klass, relation
       @readonly = false
       @associations_to_preload = []
+      @eager_load_associations = []
     end
 
     def preload(association)
-      @associations_to_preload << association
-      @associations_to_preload.flatten!
+      @associations_to_preload += association
+      self
+    end
+
+    def eager_load(association)
+      @eager_load_associations += association
+      self
     end
 
     def readonly
@@ -20,11 +26,23 @@ module ActiveRecord
     end
 
     def to_a
-      records = @klass.find_by_sql(@relation.to_sql)
-
-      @klass.send :preload_associations, records, @associations_to_preload unless @associations_to_preload.empty?
-
-      records.each { |record| record.readonly! } if @readonly
+      if @eager_load_associations.any?
+        records = catch :invalid_query do
+          @klass.send(:find_with_associations, {
+            :select => @relation.send(:select_clauses).join(', '),
+            :joins => @relation.joins(relation),
+            :group => @relation.send(:group_clauses).join(', '),
+            :order => @relation.send(:order_clauses).join(', '),
+            :conditions => @relation.send(:where_clauses).join("\n\tAND "),
+            :limit => @relation.taken
+            },
+            ActiveRecord::Associations::ClassMethods::JoinDependency.new(@klass, @eager_load_associations, nil))
+        end
+      else
+        records = @klass.find_by_sql(@relation.to_sql)
+        @klass.send(:preload_associations, records, @associations_to_preload) unless @associations_to_preload.empty?
+        records.each { |record| record.readonly! } if @readonly
+      end
 
       records
     end
diff --git a/activerecord/test/cases/associations/cascaded_eager_loading_test.rb b/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
index 45e74ea024..ed2e2e9f8f 100644
--- a/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
+++ b/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
@@ -104,7 +104,7 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
       authors.first.posts.first.special_comments.first.post.very_special_comment
     end
   end
-  
+
   def test_eager_association_loading_where_first_level_returns_nil
     authors = Author.find(:all, :include => {:post_about_thinking => :comments}, :order => 'authors.id DESC')
     assert_equal [authors(:mary), authors(:david)], authors