Added ActiveRecord::Base.find(:last) (closes #11338) [miloops]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@9012 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Added ActiveRecord::Base.find(:last) #11338 [miloops]
+
 * test_native_types expects DateTime.local_offset instead of DateTime.now.offset; fixes test breakage due to dst transition [Geoff Buesing]
 
 * Add :readonly option to HasManyThrough associations. #11156 [miloops]

activerecord/lib/active_record/base.rb

@@ -430,12 +430,14 @@ def self.reset_subclasses #:nodoc:
     @@schema_format = :ruby
 
     class << self # Class methods
-      # Find operates with three different retrieval approaches:
+      # Find operates with four different retrieval approaches:
       #
       # * Find by id: This can either be a specific id (1), a list of ids (1, 5, 6), or an array of ids ([5, 6, 10]).
       #   If no record can be found for all of the listed ids, then RecordNotFound will be raised.
       # * Find first: This will return the first record matched by the options used. These options can either be specific
       #   conditions or merely an order. If no record can be matched, nil is returned.
+      # * Find last: This will return the last record matched by the options used. These options can either be specific
+      #   conditions or merely an order. If no record can be matched, nil is returned.
       # * Find all: This will return all the records matched by the options used. If no records are found, an empty array is returned.
       #
       # All approaches accept an options hash as their last parameter. The options are:
@@ -475,6 +477,11 @@ class << self # Class methods
       #   Person.find(:first, :conditions => [ "user_name = ?", user_name])
       #   Person.find(:first, :order => "created_on DESC", :offset => 5)
       #
+      # Examples for find last:
+      #   Person.find(:last) # returns the last object fetched by SELECT * FROM people
+      #   Person.find(:last, :conditions => [ "user_name = ?", user_name])
+      #   Person.find(:last, :order => "created_on DESC", :offset => 5)
+      #
       # Examples for find all:
       #   Person.find(:all) # returns an array of objects for all the rows fetched by SELECT * FROM people
       #   Person.find(:all, :conditions => [ "category IN (?)", categories], :limit => 50)
@@ -499,6 +506,7 @@ def find(*args)
 
         case args.first
           when :first then find_initial(options)
+          when :last  then find_last(options)
           when :all   then find_every(options)
           else             find_from_ids(args, options)
         end
@@ -1236,6 +1244,35 @@ def find_initial(options)
           find_every(options).first
         end
 
+        def find_last(options)
+          order = options[:order]
+
+          if order
+            order = reverse_sql_order(order)
+          elsif !scoped?(:find, :order)
+            order = "#{table_name}.#{primary_key} DESC"
+          end
+
+          if scoped?(:find, :order)
+            scoped_order = reverse_sql_order(scope(:find, :order))
+            scoped_methods.select { |s| s[:find].update(:order => scoped_order) }
+          end
+          
+          find_initial(options.merge({ :order => order }))
+        end
+
+        def reverse_sql_order(order_query)
+          reversed_query = order_query.split(/,/).each { |s|
+            if s.match(/\s(asc|ASC)$/)
+              s.gsub!(/\s(asc|ASC)$/, ' DESC')
+            elsif s.match(/\s(desc|DESC)$/)
+              s.gsub!(/\s(desc|DESC)$/, ' ASC')
+            elsif !s.match(/\s(asc|ASC|desc|DESC)$/) 
+              s.concat(' DESC')
+            end
+          }.join(',')
+        end
+        
         def find_every(options)
           include_associations = merge_includes(scope(:find, :include), options[:include])
 

activerecord/test/cases/base_test.rb

@@ -1616,6 +1616,33 @@ def test_scoped_find_order_including_has_many_association
     end
   end
 
+  def test_find_last
+    last  = Developer.find :last
+    assert_equal last, Developer.find(:first, :order => 'id desc')
+  end
+  
+  def test_find_ordered_last
+    last  = Developer.find :last, :order => 'developers.salary ASC'
+    assert_equal last, Developer.find(:all, :order => 'developers.salary ASC').last
+  end
+
+  def test_find_reverse_ordered_last
+    last  = Developer.find :last, :order => 'developers.salary DESC'
+    assert_equal last, Developer.find(:all, :order => 'developers.salary DESC').last
+  end
+
+  def test_find_multiple_ordered_last
+    last  = Developer.find :last, :order => 'developers.name, developers.salary DESC'
+    assert_equal last, Developer.find(:all, :order => 'developers.name, developers.salary DESC').last
+  end
+  
+  def test_find_scoped_ordered_last
+    last_developer = Developer.with_scope(:find => { :order => 'developers.salary ASC' }) do
+      Developer.find(:last)
+    end
+    assert_equal last_developer, Developer.find(:all, :order => 'developers.salary ASC').last
+  end
+  
   def test_abstract_class
     assert !ActiveRecord::Base.abstract_class?
     assert LoosePerson.abstract_class?