How to create an inline formset for a reverse foreign key relationship

Question

I have a Property Model as follows =

class Property(models.Model):
    property_type = models.CharField(max_length=255, default='Apartment')
    specifications = models.CharField(max_length=255, default='Basic')
    built_up_area = models.FloatField(max_length=6, null=False, default=0)
    total_area = models.FloatField(null=False, default=0)
    number_of_bedrooms = models.CharField(max_length=3, default=1)
    number_of_bathrooms = models.CharField(max_length=3, default=1)
    number_of_parking_spaces = models.CharField(max_length=2, default=0)
    address_line_one = models.CharField(max_length=255, null=False)
    address_line_two = models.CharField(max_length=255, null=True, default=None)
    connectivity = models.CharField(max_length=255, default=None, null=True)
    neighborhood_quality = models.CharField(max_length=255, default=None,
                                            null=True)
    comments = models.CharField(max_length=255, default=None, null=True)
    city = models.ForeignKey('City')
    state = models.ForeignKey('State')
    pin_code = models.ForeignKey('PinCode')
    developer = models.ForeignKey('Developer', null=True, default=None)
    owner = models.ForeignKey('Owner', null=True, default=None)
    created_by = models.ForeignKey('custom_user.User')

    project = models.ForeignKey('Project')

    def __unicode__(self):
        return self.property_type

    class Meta:
        verbose_name_plural = 'Properties'

And a City model as follows -

class City(models.Model):
    name = models.CharField(max_length=255)
    slug = models.SlugField(unique=True)

    def save(self, *args, **kwargs):
        self.slug = slugify(self.name)
        super(City, self).save(*args, **kwargs)

    def __unicode__(self):
        return self.name

Now I want to make a single form where I can enter the Property details and while entering the city, I can enter the name of the city instead of selecting from the dropdown list.

So how do I create the inline formset using the inlineformset_factory to create the form?

==EDIT==

I've tried to use the following code to create the formset

CityFormset = inlineformset_factory(City, Property,
                                       fields=('city',),
                                       extra=0,
                                       min_num=1,
                                       can_delete=False)

Answer 1

You've misunderstood what an inline formset is. It's for editing the "many" side of a one-to-many relationship: that is, given a parent model of City, you could edit inline the various Properties that belong to that city.

You don't want a formset at all to simply edit the single City that a property can belong to. Instead, override the city field within your Property form to be a TextField, and either create a new City or find an existing one in the clean_city method.

class PropertyForm(forms.ModelForm):
    city = forms.TextField(required=True)

    class Meta:
        model = Property
        exclude = ('city',)

    def __init__(self, *args, **kwargs):
        super(PropertyForm, self).__init__(*args, **kwargs)
        if self.instance and not self.data:
            self.initial['city'] = self.instance.city.name

    def save(self, commit=True):
        city_name = self.cleaned_data['city']
        city, _ = City.objects.get_or_create(name=city_name)
        instance = self.save(commit=False)
        instance.city = city
        if commit = True:
            instance.save()
        return instance