port [9018] to 2.0 stable

git-svn-id: http://svn-commit.rubyonrails.org/rails/branches/2-0-stable@9019 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

Author: technoweenie

activerecord/CHANGELOG

@@ -1,5 +1,7 @@
 *SVN*
 
+* Ensure that ActiveRecord::Calculations disambiguates field names with the table name.  #11027 [cavalle]
+
 * Ensure that modifying has_and_belongs_to_many actions clear the query cache.  Closes #10840 [john.andrews]
 
 * Fix issue where Table#references doesn't pass a :null option to a *_type attribute for polymorphic associations.  Closes #10753 [railsjitsu]

activerecord/lib/active_record/calculations.rb

@@ -155,6 +155,7 @@ def construct_calculation_sql(operation, column_name, options) #:nodoc:
           scope           = scope(:find)
           merged_includes = merge_includes(scope ? scope[:include] : [], options[:include])
           aggregate_alias = column_alias_for(operation, column_name)
+          column_name     = "#{connection.quote_table_name(table_name)}.#{column_name}" unless column_name == "*" || column_name.to_s.include?('.')
 
           if operation == 'count'
             if merged_includes.any?

activerecord/test/associations/join_model_test.rb

@@ -536,6 +536,14 @@ def test_has_many_through_sum_uses_calculations
     assert_nothing_raised { authors(:david).comments.sum(:post_id) }
   end
 
+  def test_calculations_on_has_many_through_should_disambiguate_fields
+    assert_nothing_raised { authors(:david).categories.maximum(:id) }
+  end
+  
+  def test_calculations_on_has_many_through_should_not_disambiguate_fields_unless_necessary
+    assert_nothing_raised { authors(:david).categories.maximum("categories.id") }
+  end
+
   def test_has_many_through_has_many_with_sti
     assert_equal [comments(:does_it_hurt)], authors(:david).special_post_comments
   end