From 7f49582ac214d20258dccd222e360350591e1cce Mon Sep 17 00:00:00 2001
From: =?utf-8?q?Tarmo=20T=C3=A4nav?= <tarmo@itech.ee>
Date: Wed, 23 Jul 2008 14:57:42 +0300
Subject: [PATCH] has_many association and named_scope empty?() uses exists?({}) instead of counting.

This way the database only has to find one match using an index
instead of counting all the matches. If the association or scope
is already loaded or the association has a custom counter_sql
size check is used instead.
---
 .../associations/association_collection.rb         |    6 +++++-
 activerecord/lib/active_record/named_scope.rb      |    2 +-
 .../associations/has_many_associations_test.rb     |   16 ++++++++++++++++
 activerecord/test/cases/named_scope_test.rb        |   11 +++++++++++
 4 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/activerecord/lib/active_record/associations/association_collection.rb b/activerecord/lib/active_record/associations/association_collection.rb
index a28be9e..9c44eb9 100644
--- a/activerecord/lib/active_record/associations/association_collection.rb
+++ b/activerecord/lib/active_record/associations/association_collection.rb
@@ -206,7 +206,11 @@ module ActiveRecord
       end

       def empty?
-        size.zero?
+        if loaded? || @reflection.options[:counter_sql]
+          size.zero?
+        else
+          !exists?({})
+        end
       end

       def any?
diff --git a/activerecord/lib/active_record/named_scope.rb b/activerecord/lib/active_record/named_scope.rb
index d5a1c5f..ab842b4 100644
--- a/activerecord/lib/active_record/named_scope.rb
+++ b/activerecord/lib/active_record/named_scope.rb
@@ -137,7 +137,7 @@ module ActiveRecord
       end

       def empty?
-        @found ? @found.empty? : count.zero?
+        @found ? @found.empty? : !exists?({})
       end

       def any?
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index f8b8b1f..899e20d 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1017,4 +1017,20 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     ActiveRecord::Base.store_full_sti_class = old
   end

+  def test_empty_with_counter_sql
+    company = Firm.find(:first)
+    assert_sql /COUNT/i do
+      assert_equal false, company.clients.empty?
+    end
+  end
+
+  def test_empty?
+    company = Firm.find(:first)
+    assert_queries(1) do
+      assert_equal false, company.plain_clients.empty?
+    end
+
+    # should have used LIMIT, but because of different SQL adapters we can't check for that here.
+    assert_no_match /COUNT/i, $queries_executed.first
+  end
 end
diff --git a/activerecord/test/cases/named_scope_test.rb b/activerecord/test/cases/named_scope_test.rb
index e21ffbb..fd0b09d 100644
--- a/activerecord/test/cases/named_scope_test.rb
+++ b/activerecord/test/cases/named_scope_test.rb
@@ -231,4 +231,15 @@ class NamedScopeTest < ActiveRecord::TestCase
     assert topic.approved
     assert_equal 'lifo', topic.author_name
   end
+
+  def test_empty_should_use_exists_when_not_loaded
+    ActiveRecord::NamedScope::Scope.any_instance.expects(:exists?).with({}).returns(true)
+    assert_equal false, Topic.approved.empty?
+  end
+
+  def test_empty_should_not_use_exists_when_loaded
+    Topic.approved.to_a # load the association
+    Topic.approved.expects(:exists?).never
+    assert_equal false, Topic.approved.empty?
+  end
 end
--
1.5.6.3