Django ManytoManyField and widgets

Ok, this is my solution using above classes. I added a bunch more filters to filter it correctly, but I wanted to make the code readable here.

This is exactly what I was looking for, and I found my solution here: http://www.slideshare.net/lincolnloop/customizing-the-django-admin#stats-bottom (slide 50)

Add the following to my admin.py:

class CustomerForm(forms.ModelForm): 
    def __init__(self, *args, **kwargs):
        super(CustomerForm, self).__init__(*args, **kwargs)
        wtf = Category.objects.filter(pk=self.instance.cat_id);
        w = self.fields['categories'].widget
        choices = []
        for choice in wtf:
            choices.append((choice.id, choice.name))
        w.choices = choices


class CustomerAdmin(admin.ModelAdmin):
    list_per_page = 100
    ordering = ['submit_date',] # didnt have this one in the example, sorry
    search_fields = ['name', 'city',]
    filter_horizontal = ('categories',)
    form = CustomerForm

This filters the "categories" list without removing any functionality! (ie: i can still have my beloved filter_horizontal :))

The ModelForms is very powerful, I'm a bit surprised it's not covered more in the documentation/book.

null=True sets NULL (versus NOT NULL) on the column in your DB. Blank values for Django field types such as DateTimeField or ForeignKey will be stored as NULL in the DB.

blank determines whether the field will be required in forms. This includes the admin and your custom forms. If blank=True then the field will not be required, whereas if it's False the field cannot be blank.

The combo of the two is so frequent because typically if you're going to allow a field to be blank in your form, you're going to also need your database to allow NULL values for that field. The exception is CharFields and TextFields, which in Django are never saved as NULL. Blank values are stored in the DB as an empty string ('').

A few examples:

models.DateTimeField(blank=True) # raises IntegrityError if blank

models.DateTimeField(null=True) # NULL allowed, but must be filled out in a form

Obviously, Those two options don't make logical sense to use (though there might be a use case for null=True, blank=False if you want a field to always be required in forms, optional when dealing with an object through something like the shell.)

models.CharField(blank=True) # No problem, blank is stored as ''

models.CharField(null=True) # NULL allowed, but will never be set as NULL

CHAR and TEXT types are never saved as NULL by Django, so null=True is unnecessary. However, you can manually set one of these fields to None to force set it as NULL. If you have a scenario where that might be necessary, you should still include null=True.