Don't use `Column` for type casting in Relation calculations

activerecord/lib/active_record/relation/calculations.rb

@@ -273,7 +273,7 @@ def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
       row    = result.first
       value  = row && row.values.first
       column = result.column_types.fetch(column_alias) do
-        column_for(column_name)
+        type_for(column_name)
       end
 
       type_cast_calculated_value(value, column, operation)
@@ -336,14 +336,14 @@ def execute_grouped_calculation(operation, column_name, distinct) #:nodoc:
       Hash[calculated_data.map do |row|
         key = group_columns.map { |aliaz, col_name|
           column = calculated_data.column_types.fetch(aliaz) do
-            column_for(col_name)
+            type_for(col_name)
           end
           type_cast_calculated_value(row[aliaz], column)
         }
         key = key.first if key.size == 1
         key = key_records[key] if associated
 
-        column_type = calculated_data.column_types.fetch(aggregate_alias) { column_for(column_name) }
+        column_type = calculated_data.column_types.fetch(aggregate_alias) { type_for(column_name) }
         [key, type_cast_calculated_value(row[aggregate_alias], column_type, operation)]
       end]
     end
@@ -370,24 +370,20 @@ def column_alias_for(keys)
       @klass.connection.table_alias_for(table_name)
     end
 
-    def column_for(field)
+    def type_for(field)
       field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split('.').last
-      @klass.columns_hash[field_name]
+      @klass.type_for_attribute(field_name)
     end
 
-    def type_cast_calculated_value(value, column, operation = nil)
+    def type_cast_calculated_value(value, type, operation = nil)
       case operation
         when 'count'   then value.to_i
-        when 'sum'     then type_cast_using_column(value || 0, column)
+        when 'sum'     then type.type_cast_from_database(value || 0)
         when 'average' then value.respond_to?(:to_d) ? value.to_d : value
-        else type_cast_using_column(value, column)
+        else type.type_cast_from_database(value)
       end
     end
 
-    def type_cast_using_column(value, column)
-      column ? column.type_cast_from_database(value) : value
-    end
-
     # TODO: refactor to allow non-string `select_values` (eg. Arel nodes).
     def select_for_count
       if select_values.present?

activerecord/test/cases/calculations_test.rb

@@ -53,11 +53,6 @@ def test_should_return_nil_as_average
     assert_nil NumericData.average(:bank_balance)
   end
 
-  def test_type_cast_calculated_value_should_convert_db_averages_of_fixnum_class_to_decimal
-    assert_equal 0, NumericData.all.send(:type_cast_calculated_value, 0, nil, 'avg')
-    assert_equal 53.0, NumericData.all.send(:type_cast_calculated_value, 53, nil, 'avg')
-  end
-
   def test_should_get_maximum_of_field
     assert_equal 60, Account.maximum(:credit_limit)
   end