Add ActiveRecord::Base.exists? with no args [#1817 state:committed]

Signed-off-by: David Heinemeier Hansson <david@loudthinking.com>

activerecord/CHANGELOG

@@ -1,3 +1,8 @@
+*Edge*
+
+* Added that ActiveRecord::Base.exists? can be called with no arguments #1817 [Scott Taylor]
+
+
 *2.3.0 [RC1] (February 1st, 2009)*
 
 * Add Support for updating deeply nested models from a single form. #1202 [Eloy Duran]

activerecord/lib/active_record/base.rb

@@ -663,7 +663,7 @@ module ActiveRecord #:nodoc:
 
 
       # Returns true if a record exists in the table that matches the +id+ or
-      # conditions given, or false otherwise. The argument can take four forms:
+      # conditions given, or false otherwise. The argument can take five forms:
       #
       # * Integer - Finds the record with this primary key.
       # * String - Finds the record with a primary key corresponding to this
@@ -672,6 +672,7 @@ module ActiveRecord #:nodoc:
       #   (such as <tt>['color = ?', 'red']</tt>).
       # * Hash - Finds the record that matches these +find+-style conditions
       #   (such as <tt>{:color => 'red'}</tt>).
+      # * No args - Returns false if the table is empty, true otherwise.
       #
       # For more information about specifying conditions as a Hash or Array,
       # see the Conditions section in the introduction to ActiveRecord::Base.
@@ -685,7 +686,8 @@ module ActiveRecord #:nodoc:
       #   Person.exists?('5')
       #   Person.exists?(:name => "David")
       #   Person.exists?(['name LIKE ?', "%#{query}%"])
-      def exists?(id_or_conditions)
+      #   Person.exists?
+      def exists?(id_or_conditions = {})
         connection.select_all(
           construct_finder_sql(
             :select     => "#{quoted_table_name}.#{primary_key}",

activerecord/test/cases/finder_test.rb

@@ -95,6 +95,15 @@ class FinderTest < ActiveRecord::TestCase
     assert_raise(NoMethodError) { Topic.exists?([1,2]) }
   end
   
+  def test_exists_returns_true_with_one_record_and_no_args
+    assert Topic.exists?
+  end
+  
+  def test_does_not_exist_with_empty_table_and_no_args_given
+    Topic.delete_all
+    assert !Topic.exists?
+  end
+  
   def test_exists_with_aggregate_having_three_mappings
     existing_address = customers(:david).address
     assert Customer.exists?(:address => existing_address)