Creating a ModelForm where my primary key field generates a select box

I am not sure if my language clear enough but basically I have this form:

class Paper(models.Model):
    number = models.CharField(max_length=12,primary_key=True)
    project = models.ForeignKey(Project)

class SomeForm(forms.ModelForm):

    class Meta:
        model = Paper
        fields = ('project', 'number开发者_如何学运维')

and django creates a textfield for me. What I want is a select box with the existing primary keys.

Thanks.

---

I don't think you want a modelform - that's for creating and updating model instances. It sounds like you just want a form to select IDs. Use a normal form, but with a ModelChoiceField.

class SomeForm(forms.Form):
    ids = forms.ModelChoiceField(queryset=Paper.objects.all())

You'll need to give the Paper model a __unicode__ method that returns self.number.