ManyToManyField causes invalid form when limit_choices_to argument set

[rgreene]

Good day,

This is a somewhat contrived example, but I'm having the same problem in a real project.

Assuming continents have many countries, and countries can belong to many continents, I have a continent_country "junction" table in the database and am using ManyToManyField as follows...

Models:

class Country(models.Model):

    country_id = models.AutoField(primary_key=True)

    country_name = models.CharField(max_length=200)

    class Meta:

        managed = False

        db_table = 'country'

    def __unicode__(self):

        return '%s' % (self.country_name)

class Continent(models.Model):

    continent_id = models.AutoField(primary_key=True)

    continent_name = models.CharField(max_length=200)

    country = models.ManyToManyField(Country, db_table='continent_country', limit_choices_to=Q(country_id__exact=1))

    class Meta:

        managed = False

        db_table = 'continent'

Form:

class ContinentForm(ModelForm):

    class Meta:

        model = Continent

        widgets = {'country': CheckboxSelectMultiple}

Using this form, everything saves as expected if I remove the limit_choices_to=Q(country_id__exact=1)argument. However, using the form with the ManyToManyField configured as shown causes the form to be returned with is_valid=False in the POST, indicating that field country is required.

I traced into the django code for a bit, but as a relative rookie got somewhat lost! Why does limiting the list prevent django from setting the country? How to work around this? Any ideas greatly appreciated...

Thanks in advance,

Randal

[rgreene]

Solved! It turned out the problem only occurred trying to uncheck the last checkbox. I needed to set blank=True on the ManyToManyField.