Django Column 'id' cannot be null

I am having a weird problem with my mysql database and django.

I created an app with a model imported from an existing database with inspectdb. It was working fine until yesterday I removed the django automatically created tables (django_, auth_, site_*). I did that because it was preventing my model to validate when I added my app in the installed apps.

Now开发者_Go百科 today I tried inserting a new record in my database and I get the following error :

Django Version:     1.3
Exception Type:     IntegrityError
Exception Value: (1048, "Column 'asset_id' cannot be null")

The field is a primary key and it's supposed to be auto_increment so I don't give a value to it when I create a new record.

Can someone point me what's going on here ?

EDIT : I partly figured out the problem : somehow all my auto_increment proprities were removed from my database. How did that happen ?

Check your generated models, and ensure that the "auto_increment" columns correspond with fields marked with the primary_key=True option.

May be you need to save your object model, before obtain id property.