Free-form input for ForeignKey Field on a Django ModelForm

Question

I have two models related by a foreign key:

# models.py    
class TestSource(models.Model):
  name        = models.CharField(max_length=100)

class TestModel(models.Model):
  name        = models.CharField(max_length=100)
  attribution = models.ForeignKey(TestSource, null=True)

By default, a django ModelForm will present this as a <select> with <option>s; however I would prefer that this function as a free form input, <input type="text"/>, and behind the scenes get or create the necessary TestSource object and then relate it to the TestModel object.

I have tried to define a custom ModelForm and Field to accomplish this:

# forms.py
class TestField(forms.TextInput):
  def to_python(self, value):
    return TestSource.objects.get_or_create(name=value)

class TestForm(ModelForm):
  class Meta:
    model=TestModel
    widgets = {
      'attribution' : TestField(attrs={'maxlength':'100'}),
    }

Unfortunately, I am getting: invalid literal for int() with base 10: 'test3' when attempting to check is_valid on the submitted form. Where am I going wrong? Is their and easier way to accomplish this?

Answer 1

Something like this should work:

class TestForm(ModelForm):
  attribution = forms.CharField(max_length=100)

  def save(self, commit=True):
      attribution_name = self.cleaned_data['attribution']
      attribution = TestSource.objects.get_or_create(name=attribution_name)[0]  # returns (instance, <created?-boolean>)
      self.instance.attribution = attribution

      return super(TestForm, self).save(commit)

  class Meta:
    model=TestModel
    exclude = ('attribution')

Answer 2

There are a few problems here.

Firstly, you have defined a field, not a widget, so you can't use it in the widgets dictionary. You'll need to override the field declaration at the top level of the form.

Secondly get_or_create returns two values: the object retrieved or created, and a boolean to show whether or not it was created. You really just want to return the first of those values from your to_python method.

I'm not sure if either of those caused your actual error though. You need to post the actual traceback for us to be sure.