explicitly including child associations that are also included in the parent association definition should not result in double records in the collection/double loads (#1110)

Signed-off-by: Michael Koziarski <michael@koziarski.com>
[#1110 state:committed]

activerecord/lib/active_record/association_preload.rb

@@ -193,6 +193,7 @@ module ActiveRecord
       end
 
       def preload_has_one_association(records, reflection, preload_options={})
+        return if records.first.send("loaded_#{reflection.name}?")
         id_to_record_map, ids = construct_id_map(records)        
         options = reflection.options
         records.each {|record| record.send("set_#{reflection.name}_target", nil)}
@@ -214,6 +215,7 @@ module ActiveRecord
       end
 
       def preload_has_many_association(records, reflection, preload_options={})
+        return if records.first.send(reflection.name).loaded?
         options = reflection.options
 
         primary_key_name = reflection.through_reflection_primary_key_name
@@ -271,6 +273,7 @@ module ActiveRecord
       end
 
       def preload_belongs_to_association(records, reflection, preload_options={})
+        return if records.first.send("loaded_#{reflection.name}?")
         options = reflection.options
         primary_key_name = reflection.primary_key_name
 

activerecord/lib/active_record/associations.rb

@@ -1248,6 +1248,11 @@ module ActiveRecord
             association.target.nil? ? nil : association
           end
 
+          define_method("loaded_#{reflection.name}?") do
+            association = instance_variable_get(ivar) if instance_variable_defined?(ivar)
+            association && association.loaded?
+          end
+
           define_method("#{reflection.name}=") do |new_value|
             association = instance_variable_get(ivar) if instance_variable_defined?(ivar)
 

activerecord/test/cases/associations/eager_test.rb

@@ -18,7 +18,7 @@ require 'models/developer'
 require 'models/project'
 
 class EagerAssociationTest < ActiveRecord::TestCase
-  fixtures :posts, :comments, :authors, :categories, :categories_posts,
+  fixtures :posts, :comments, :authors, :author_addresses, :categories, :categories_posts,
             :companies, :accounts, :tags, :taggings, :people, :readers,
             :owners, :pets, :author_favorites, :jobs, :references, :subscribers, :subscriptions, :books,
             :developers, :projects, :developers_projects
@@ -111,6 +111,46 @@ class EagerAssociationTest < ActiveRecord::TestCase
     end
   end
 
+  def test_finding_with_includes_on_has_many_association_with_same_include_includes_only_once
+    author_id = authors(:david).id
+    author = assert_queries(3) { Author.find(author_id, :include => {:posts_with_comments => :comments}) } # find the author, then find the posts, then find the comments
+    author.posts_with_comments.each do |post_with_comments|
+      assert_equal post_with_comments.comments.length, post_with_comments.comments.count
+      assert_equal nil, post_with_comments.comments.uniq!
+    end
+  end
+
+  def test_finding_with_includes_on_has_one_assocation_with_same_include_includes_only_once
+    author = authors(:david)
+    post = author.post_about_thinking_with_last_comment
+    last_comment = post.last_comment
+    author = assert_queries(3) { Author.find(author.id, :include => {:post_about_thinking_with_last_comment => :last_comment})} # find the author, then find the posts, then find the comments
+    assert_no_queries do
+      assert_equal post, author.post_about_thinking_with_last_comment
+      assert_equal last_comment, author.post_about_thinking_with_last_comment.last_comment
+    end
+  end
+
+  def test_finding_with_includes_on_belongs_to_association_with_same_include_includes_only_once
+    post = posts(:welcome)
+    author = post.author
+    author_address = author.author_address
+    post = assert_queries(3) { Post.find(post.id, :include => {:author_with_address => :author_address}) } # find the post, then find the author, then find the address
+    assert_no_queries do
+      assert_equal author, post.author_with_address
+      assert_equal author_address, post.author_with_address.author_address
+    end
+  end
+
+  def test_finding_with_includes_on_null_belongs_to_association_with_same_include_includes_only_once
+    post = posts(:welcome)
+    post.update_attributes!(:author => nil)
+    post = assert_queries(2) { Post.find(post.id, :include => {:author_with_address => :author_address}) } # find the post, then find the author which is null so no query for the address
+    assert_no_queries do
+      assert_equal nil, post.author_with_address
+    end
+  end
+
   def test_loading_from_an_association
     posts = authors(:david).posts.find(:all, :include => :comments, :order => "posts.id")
     assert_equal 2, posts.first.comments.size

activerecord/test/models/author.rb

@@ -17,6 +17,8 @@ class Author < ActiveRecord::Base
       proxy_target
     end
   end
+  has_one  :post_about_thinking, :class_name => 'Post', :conditions => "posts.title like '%thinking%'"
+  has_one  :post_about_thinking_with_last_comment, :class_name => 'Post', :conditions => "posts.title like '%thinking%'", :include => :last_comment
   has_many :comments, :through => :posts
   has_many :comments_containing_the_letter_e, :through => :posts, :source => :comments
   has_many :comments_with_order_and_conditions, :through => :posts, :source => :comments, :order => 'comments.body', :conditions => "comments.body like 'Thank%'"

activerecord/test/models/post.rb

@@ -13,6 +13,7 @@ class Post < ActiveRecord::Base
   end
 
   belongs_to :author_with_posts, :class_name => "Author", :foreign_key => :author_id, :include => :posts
+  belongs_to :author_with_address, :class_name => "Author", :foreign_key => :author_id, :include => :author_address
 
   has_one :last_comment, :class_name => 'Comment', :order => 'id desc'