Always return decimal average of integer fields

In previous version if database adapter (e.g. SQLite and Oracle) returned non-String calculated values then type_cast_using_column converted decimal average value of intefer field to integer value. Now operation parameter is always checked to decide which conversion of calculated value should be done.

activerecord/lib/active_record/relation/calculations.rb

@@ -282,15 +282,11 @@ def column_for(field)
     end
 
     def type_cast_calculated_value(value, column, operation = nil)
-      if value.is_a?(String) || value.nil?
-        case operation
-          when 'count'   then value.to_i
-          when 'sum'     then type_cast_using_column(value || '0', column)
-          when 'average' then value.try(:to_d)
-          else type_cast_using_column(value, column)
-        end
-      else
-        type_cast_using_column(value, column)
+      case operation
+        when 'count'   then value.to_i
+        when 'sum'     then type_cast_using_column(value || '0', column)
+        when 'average' then value.try(:to_d)
+        else type_cast_using_column(value, column)
       end
     end
 

activerecord/test/cases/calculations_test.rb

@@ -23,6 +23,11 @@ def test_should_average_field
     assert_equal 53.0, value
   end
 
+  def test_should_return_decimal_average_of_integer_field
+    value = Account.average(:id)
+    assert_equal 3.5, value
+  end
+
   def test_should_return_nil_as_average
     assert_nil NumericData.average(:bank_balance)
   end