Danger with django ModelForms and related names

There is a danger in extending your ModelForms with fields if you don’t take care of your naming. Take for example these models. The forms represents a simple batch emailing module.

#!/usr/bin/python/

class EmailBatch(models.Model):
    body = models.TextField()
    subject = models.CharField(max_length=400)

class Email(models.Model):
    batch = models.ForeignKey(EmailBatch, null=False, related_name="emails")
    recipient = models.EmailField()

I wrote a simple form field called MultipleEmailField so the users can input several email addresses in a simple textarea. The resulting form is something like this:

#!/usr/bin/python/

class SendingForm(forms.ModelForm):
    emails = MultiEmailField(required=True)

    class EmailBatch:
        model = Delivery
        fields = ('body', 'subject', )

This appears to be alright, but isn’t. If you use this form you’ll get an AttributeError. The problem is in handling the “emails” field on the form. It’s not bound to any model, but the model actually contains something called emails (it’s set in the related_name part of the Email model). This can take some time to find :(

The bug is already fixed in django trunk, but for those of us trying to use a stable version we’ll just have to wait a little longer.

A simple fix is just to rename your field or related name