Added ActiveRecord::Base#becomes to turn a record into one of another class (mostly relevant for STIs) [DHH]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8259 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

@@ -1,5 +1,9 @@
 *SVN*
 
+* Added ActiveRecord::Base#becomes to turn a record into one of another class (mostly relevant for STIs) [DHH]. Example:
+
+    render :partial => @client.becomes(Company) # renders companies/company instead of clients/client
+
 * Fixed that to_xml should not automatically pass :procs to associations included with :include #10162 [chuyeow]
 
 * Fix documentation typo introduced in [8250]. Closes #10339 [Henrik N]

activerecord/lib/active_record/base.rb

@@ -1806,6 +1806,20 @@ module ActiveRecord #:nodoc:
         record
       end
 
+      # Returns an instance of the specified klass with the attributes of the current record. This is mostly useful in relation to
+      # single-table inheritance structures where you want a subclass to appear as the superclass. This can be used along with record
+      # identification in Action Pack to allow, say, Client < Company to do something like render :partial => @client.becomes(Company)
+      # to render that instance using the companies/company partial instead of clients/client.
+      #
+      # Note: The new instance will share a link to the same attributes as the original class. So any change to the attributes in either
+      # instance will affect the other.
+      def becomes(klass)
+        returning klass.new do |became|
+          became.instance_variable_set("@attributes", @attributes)
+          became.instance_variable_set("@new_record", new_record?)
+        end
+      end
+
       # Updates a single attribute and saves the record. This is especially useful for boolean flags on existing records.
       # Note: This method is overwritten by the Validation module that'll make sure that updates made with this method
       # aren't subjected to validation checks. Hence, attributes can be updated even if the full object isn't valid.

activerecord/test/base_test.rb

@@ -1737,4 +1737,9 @@ class BasicsTest < Test::Unit::TestCase
     assert_equal %("#{t.written_on.to_s(:db)}"), t.attribute_for_inspect(:written_on)
     assert_equal '"This is some really long content, longer than 50 ch..."', t.attribute_for_inspect(:content)
   end
-end
+  
+  def test_becomes
+    assert_kind_of Reply, topics(:first).becomes(Reply)
+    assert_equal "The First Topic", topics(:first).becomes(Reply).title
+  end
+end