Saving a model in Django gives me "Warning: Field 'id' doesn't have a default value"

Question

I have a very basic model in Django:

class Case(models.Model):
    name = models.CharField(max_length=255)
    created_at = models.DateTimeField(default=datetime.now)
    updated_at = models.DateTimeField(default=datetime.now)

    def save(self):
        if self.created_at == None:
             self.created_at = datetime.now()
        self.updated_at = datetime.now()
        super(Case, self).save()

    class Meta:
        db_table = u'cases'

Because I did not specify the PK, Django took care of that for me. I see the field in my database which is called "id", marked as a primary key and auto-increment. I find odd to be getting that warning since everything is cool on the DB and model end. The error is:

_mysql_exceptions.Warning

Warning: Field 'id' doesn't have a default value

My work around when saving is to set the id to 0. It kills the warning and the id gets set properly anyway since MySQL handles it.

case = Case()
case.id = 0 #ugly workaround for - Warning: Field 'id' doesn't have a default value
case.name = request.POST[u'case[name]']
case.save()

The issue with this solution is:

1. It's ugly
2. The new PK is inaccessible after saving which makes it impossible to serialize properly

Does anyone know how to fix this?

I'm running:

Python 2.7.2
django.VERSION (1, 3, 1, 'final', 0)
mysql  Ver 14.14 Distrib 5.1.45, for apple-darwin10.2.0 (i386) using readline 5.1
MySQL_python-1.2.3-py2.7-macosx-10.4-x86_64.egg

And my create table looks like this:

CREATE TABLE `cases` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) NOT NULL,
  `created_at` datetime NOT NULL,
  `updated_at` datetime NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=MyISAM AUTO_INCREMENT=45 DEFAULT CHARSET=latin1

Answer 1

I'd like to expand on this question as I've ran into it this week. I was getting this same exact error and taking a look at the model definition and SQL definition showed that:

1. The models affected either had no PK explicitly defined or had a PK explicitly defined (both had problems). This alone seemed unrelated.

2. The tables affected had the "id" definition as in the OP, i.e. id int(11) NOT NULL AUTO_INCREMENT. The PRIMARY KEY is set as expected.

3. Looking into the MySQL query log I got something to this extent:

   INSERT INTO `x` (...) VALUES (...)
   SHOW WARNINGS
   ROLLBACK
   

   Running the query individually is successful, and SHOW WARNINGS reflects the warning noted in the OP.

I however came across a MySQL-end fix, http://webit.ca/2012/01/field-id-doesnt-have-a-default-value/ mentioned that resetting the id definition (which at a cursory glance appears to not be any different) fixes the problem. I can't explain why this works, but it addresses the problem without any additional code changes. I believe this may be in some way linked to removing records, but the whole issue seems non-sensical to me.