Rails - Feb 2005 - [Error] Using validates_presence_of for datetime field causes parse error?

Hi Everyone -

I''ve got an odd sort of error when I try to use validates_presence_of  
for a MySQL ''datetime'' field. Here''s the relevant
portion of the table
definition:

mysql> describe student_surveys;
+---------------------+---------------------+------+----- 
+---------------------+----------------+
| Field               | Type                | Null | Key | Default       
        | Extra          |
+---------------------+---------------------+------+----- 
+---------------------+----------------+
| id                  | int(11)             |      | PRI | NULL          
        | auto_increment |
<snip>
| creation_date       | datetime            |      |     | 0000-00-00  
00:00:00 |                |

In my model, I have

	    validates_presence_of :creation_date

And the relevant portion of the unit testing ruby file is:

     def setup
         @student_survey = StudentSurvey.new
         #<snip>
         @student_survey.creation_date = DateTime.now
     end

     def test_create
         @student_survey.save
     end

When I run this unit test, I get:

   1) Error:
test_create(StudentSurveyTest):
NoMethodError: private method `gsub!'' called for #<DateTime:  
11776418931730081/4800000000,-5/24,2299161>
     /usr/lib/ruby/1.8/date/format.rb:238:in `_parse''
     /usr/lib/ruby/1.8/parsedate.rb:9:in `parsedate''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
connection_adapters/abstract_adapter.rb:228:in `string_to_time''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
connection_adapters/abstract_adapter.rb:196:in `type_cast''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
base.rb:1054:in `read_attribute''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
base.rb:1031:in `method_missing''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
validations.rb:443:in `send''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
validations.rb:443:in `add_on_empty''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
validations.rb:442:in `each''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
validations.rb:442:in `add_on_empty''
      
/usr/lib/ruby/gems/1.8/gems/activerecord-1.6.0/lib/active_record/ 
validations.rb:378:in `run_validations''
<snip>

What gives? If I change my unit test''s setup method to assign  
DateTime.now.asctime to my creation_date field, it works, but why can''t
I just store a DateTime object in the Active Record object''s field?

Thanks for any suggestions!

- Sean