Ensure Arel columns are typecasted properly when grouping with calculation

Fix build issue with postgresql.

activerecord/lib/active_record/relation/calculations.rb

@@ -265,9 +265,9 @@ def execute_grouped_calculation(operation, column_name, distinct) #:nodoc:
       group_attrs = group_values
 
       if group_attrs.first.respond_to?(:to_sym)
-        association = @klass.reflect_on_association(group_attrs.first.to_sym)
-        associated  = group_attrs.size == 1 && association && association.macro == :belongs_to # only count belongs_to associations
-        group_fields  = Array(associated ? association.foreign_key : group_attrs)
+        association  = @klass.reflect_on_association(group_attrs.first.to_sym)
+        associated   = group_attrs.size == 1 && association && association.macro == :belongs_to # only count belongs_to associations
+        group_fields = Array(associated ? association.foreign_key : group_attrs)
       else
         group_fields = group_attrs
       end
@@ -313,10 +313,10 @@ def execute_grouped_calculation(operation, column_name, distinct) #:nodoc:
       end
 
       Hash[calculated_data.map do |row|
-        key   = group_columns.map { |aliaz, column|
+        key = group_columns.map { |aliaz, column|
           type_cast_calculated_value(row[aliaz], column)
         }
-        key   = key.first if key.size == 1
+        key = key.first if key.size == 1
         key = key_records[key] if associated
         [key, type_cast_calculated_value(row[aggregate_alias], column_for(column_name), operation)]
       end]
@@ -343,7 +343,7 @@ def column_alias_for(*keys)
     end
 
     def column_for(field)
-      field_name = field.to_s.split('.').last
+      field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split('.').last
       @klass.columns.detect { |c| c.name.to_s == field_name }
     end
 

activerecord/test/cases/calculations_test.rb

@@ -58,12 +58,16 @@ def test_should_get_minimum_of_field
 
   def test_should_group_by_field
     c = Account.group(:firm_id).sum(:credit_limit)
-    [1,6,2].each { |firm_id| assert c.keys.include?(firm_id) }
+    [1,6,2].each do |firm_id|
+      assert c.keys.include?(firm_id), "Group #{c.inspect} does not contain firm_id #{firm_id}"
+    end
   end
 
   def test_should_group_by_arel_attribute
-    c = Account.sum(:credit_limit, :group => Account.arel_table[:firm_id])
-    [1,6,2].each { |firm_id| assert c.keys.include?(firm_id) }
+    c = Account.group(Account.arel_table[:firm_id]).sum(:credit_limit)
+    [1,6,2].each do |firm_id|
+      assert c.keys.include?(firm_id), "Group #{c.inspect} does not contain firm_id #{firm_id}"
+    end
   end
 
   def test_should_group_by_multiple_fields