class ContactForm(models.Model):

Solution:

ModelForm only have save method
Form doesn’t have save method so

class ContactForm(forms.ModelForm):

If you have a list in your session, append operations don’t get saved to the object.

Solution

Copy the list out of the session object, append to it, then copy it back in:

sessionlist = request.session[’my_list‘]
sessionlist.append(new_object)
request.session[’my_list‘] = sessionlist

When you have a Field: current_zip = meta.IntegerField(maxlength=5,blank=True)

django will create a not nullable field in the DB. However leaving the field blank (in admin/web) django will try and insert a NULL value in the DB.

Solution

Add null=True:

current_zip = meta.IntegerField(maxlength=5,null=True,blank=True)

The automatic admin interface is showing nothing (or a single ) in the “Select [object_type] to change” view.

Probable cause

You may have forgotten to create a __str__() function for your model. Django calls __str__() to find out how to display objects in the admin interface. An alternate cause is the string you return from __str__() includes brackets (an therefore looks like an html tag), and is cleaned up by the strip_tags template filter, resulting in blank entries.

Solution

Add a correct __str__() function (without brackets in the output) to all your models. Make it a habit so it becomes automatic.

You’re using SQLite3, your DATABASE_NAME is set to the database file’s full path, the database file is writeable by Apache, but you still get the above error.

Solution

Make sure Apache can also write to the parent directory of the database. SQLite needs to be able to write to this directory.

Make sure each folder of your database file’s full path does not start with number, eg. /www/4myweb/db (observed on Windows 2000).

A model does not validate with the following message:

Validating models...
project.allication: Error when calling the metaclass bases
unbound method contribute_to_class() must be called with TextField instance as first argument (got ModelBase instance instead)
1 error found.

Possible Cause

A model field was not declared properly, the parentheses after the field types name were missing:

wrong:

class Content(models.Model):
content = models.TextField

correct:

class Content(models.Model):
content = models.TextField()

Solution

A model field is an instance of the appropriate Field class, so the parentheses are required.

After creating a new application, with a model that validates, trying to log on to the admin causes an error similar to:

ImproperlyConfigured: Error importing middleware django.middleware.common: “No module named … “

Possible cause

Check to see that you didn’t use a reserved name in naming your application, i.e. “email”, “date” and “time” are common application names that would validate when the server starts but will break Django’s admin.

Solution

Rename your application directory using a non-reserved name, i.e., “email_app” instead of “email”. Go into the INSTALLED_APPS section of settings.py and change the name there too. Also, don’t forget to do a syncdb to create the newly renamed app in your database. You may also want to go in to your database and drop the old “mis-named” table.

You have been playing with the database API and noticed that a returned query set looks a lot like a list:

>>> from mysite.polls.models import Poll,Choice
>>> Poll.objects.all()
[<Poll: What is up?>, <Poll: What is your favourite colour?>]  ## looks a lot like a list to me

But, it doesn’t behave like a list in some cases.

Solution

Here are a couple of cases where the behaviour is not list-like and their solution.

In Python this is how we can test for an empty list:

>>> b=[]
>>> b==[]
True

This doesn’t work with a QuerySet?. You might try the following but it will fail:

>>> from mysite.polls.models import Poll,Choice
>>> p = Poll.objects.filter(question__startswith=‘ZZZZZZZZZZZZ’)
>>> p
[]
>>> p==[]
False

The way to do it is test for p.count:

>>> from mysite.polls.models import Poll,Choice
>>> p = Poll.objects.filter(question__startswith=‘ZZZZZZZZZZZZ’)
>>> p
[]
>>> p.count() == 0
True

Another case occurs when you want to retrieve the last member of a QuerySet?:

>>> from mysite.polls.models import Poll,Choice
>>> p = Poll.objects.all()
>>> p
[<Poll: What is up?>, <Poll: What is your favourite colour?>]
>>> p[-1]
Traceback (most recent call last):
File “<console>”, line 1, in ?
File “c:\python24\lib\site-packages\django-0.95-py2.4.egg\django\db\models\query.py”, line 98, in
__getitem__
assert (not isinstance(k, slice) and (k >= 0)) \
AssertionError: Negative indexing is not supported.

The way I get the last member is:

>>> p[p.count()-1]
<Poll: What is your favourite colour?>

You have no clue how to map a media url to your media directory when using apache2.

Solution

Use the Alias Directive and don’t forget to set-up access rights correctly.

Alias /mediaurl /path/to/files
<Directory /path/to/files>
Order allow,deny
Allow from all
</Directory>