Change Base#to_xml to take the name for a container element for an association...

Change Base#to_xml to take the name for a container element for an association from the element name, not the first record's class name.  Closes #7004

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6654 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/CHANGELOG

 *SVN*
 
+* Use association name for the wrapper element when using .to_xml.  Previous behaviour lead to non-deterministic situations with STI and polymorphic associations. [Koz, jstrachan]
+
 * Improve performance of calling .create on has_many :through associations. [evan]
 
 * Improved cloning performance by relying less on exception raising #8159 [Blaine]

activerecord/lib/active_record/xml_serialization.rb

@@ -204,11 +204,11 @@ def add_includes
           when :has_many, :has_and_belongs_to_many
             records = @record.send(association).to_a
             unless records.empty?
-              tag = records.first.class.to_s.underscore.pluralize
+              tag = association.to_s
               tag = tag.dasherize if dasherize?
 
               builder.tag!(tag) do
-                records.each { |r| r.to_xml(opts.merge(:root => association.to_s.singularize)) }
+                records.each { |r| r.to_xml(opts.merge(:root=>r.class.to_s.underscore)) }
               end
             end
           when :has_one, :belongs_to

activerecord/test/xml_serialization_test.rb

@@ -133,7 +133,8 @@ def test_should_serialize_yaml
 class DatabaseConnectedXmlSerializationTest < Test::Unit::TestCase
   fixtures :authors, :posts
   # to_xml used to mess with the hash the user provided which
-  # caused the builder to be reused
+  # caused the builder to be reused.  This meant the document kept
+  # getting appended to.
   def test_passing_hash_shouldnt_reuse_builder
     options = {:include=>:posts}
     david = authors(:david)
@@ -141,4 +142,10 @@ def test_passing_hash_shouldnt_reuse_builder
     second_xml_size = david.to_xml(options).size
     assert_equal first_xml_size, second_xml_size
   end
+  
+
+  def test_include_uses_association_name
+    xml = authors(:david).to_xml :include=>:hello_posts, :indent=>0
+    assert(xml.include?(%(<hello_posts><post>)) || xml.include?(%(</post></hello-posts>)))
+  end
 end
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