How to assign default value to Django model Integerfield, while related FormField is optional?

Question

I want to create a Django model Field (IntegerField) with a default value, and also create a form derived from the model, where the field is optional. If it's not set on the form, then when I save the form, I want the default value saved to the DB.

# model.py
class Invoice(models.Model):
    # IntegrityError "Column 'expireDays' cannot be null"
    expireDays = models.PositiveSmallIntegerField(default=1)

    # expireDays = *null* in DB
    expireDays = models.PositiveSmallIntegerField(default=1, blank=True, null=True)

# forms.py
class InvoiceForm(forms.ModelForm):
    # leaving this line out gives invalid form
    expireDays = forms.IntegerField(required=False)
    class Meta:
        model = Invoice

(I used only one of the field declaration lines at a time. :)

I'm not even sure that I'm declaring the default value correctly. The only reference I could find to it was in an article on handling choices by James Bennett. I have yet to find it in the Django docs (I'm using version 1.2 - maybe it's in 1.3?)

Update - I tried setting the field's default value in the MySql database, to no effect. It seems as if, even when the form does not have a value for the field, it goes ahead and assigns null to the DB, over-riding the MySql default value.

Although I am currently just setting a default value in the view that creates the form - I don't really like that, since it puts the responsibility for the field's integrity in the view, not the DB.

The way I would have thought it would work, is that the field could be set, or not, in the form - if set, that value would be written to the DB, and if not set, the DB default would be used. Instead, if not set, the form is writing a null to the DB. So what's the point of having a default value in the ModelField declaration if it's not used? What exactly does it do?

Jerzyk · Accepted Answer · 2011-05-17 22:03:16Z

23

i you want field to be optional - just leave second definition in the model and do not add anything in the form definition:

class Invoice(models.Model):
    expireDays = models.PositiveSmallIntegerField(default=1, blank=True, null=True)

class InvoiceForm(forms.ModelForm):
    class Meta:
        model = Invoice

update, so in case there is no value set, use 1 as the field value:

class InvoiceForm(forms.ModelForm):

    def clean_expireDays(self):
        exp_days = self.cleaned_data.get('expireDays')
        if exp_days is None:
            return self.fields['expireDays'].initial
            # above can be: return 1
            # but now it takes value from model definition
        else:
            return exp_days

    class Meta:
        model = Invoice

edited May 17, 2011 at 22:03

answered May 15, 2011 at 23:24

Jerzyk

3,77227 silver badges41 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

John C Over a year ago

My post may not have been clear, but that is one of the combinations I tried - and the MySql data field shows up as null when I do that, not a 1.

John C Over a year ago

Comment on the update - actually, I'm doing it another way - setting the field in the (copied) POST data to a default of 1, before passing the POST data to the form. But that still puts the logic for maintaining data integrity inside the form, and not the database where I want it. The MySql db should be assigning the default value. What I would have expected to happen, is if the form didn't get a value, it wouldn't try to set the DB value - but it seems to be assigning a NULL to the DB, which over-rides even the default value I set by hand in the DB.

Collectives™ on Stack Overflow

How to assign default value to Django model Integerfield, while related FormField is optional?

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related