Add relation.exists?

activerecord/CHANGELOG

@@ -1,5 +1,11 @@
 *Edge*
 
+* Add relation.exists? [Pratik Naik]
+
+  red_items = Item.where(:colours => 'red')
+  red_items.exists?
+  red_items.exists?(1)
+
 * Add find(ids) to relations. [Pratik Naik]
 
   old_users = User.order("age DESC")

activerecord/lib/active_record/relation.rb

@@ -139,6 +139,12 @@ module ActiveRecord
       end
     end
 
+    def exists?(id = nil)
+      relation = select("#{@klass.quoted_table_name}.#{@klass.primary_key}").limit(1)
+      relation = relation.where(@klass.primary_key => id) if id
+      relation.first ? true : false
+    end
+
     def first
       if loaded?
         @records.first

activerecord/test/cases/relations_test.rb

@@ -298,4 +298,15 @@ class RelationTest < ActiveRecord::TestCase
     assert_raises(ActiveRecord::RecordNotFound) { authors.find(['invalid', 'oops']) }
   end
 
+  def test_exists
+    davids = Author.where(:name => 'David')
+    assert davids.exists?
+    assert davids.exists?(authors(:david).id)
+    assert ! davids.exists?(authors(:mary).id)
+    assert ! davids.exists?("hax'id")
+
+    fake  = Author.where(:name => 'fake author')
+    assert ! fake.exists?
+    assert ! fake.exists?(authors(:david).id)
+  end
 end