Django Model Choice Field: Huge List of choices

Consider these 3 models:

# models.py
class City(models.Model):
    name = models.CharField(max_length=50)

class Institute(models.Model):
    name = models.CharField(max_length=100)
    city = models.ForeignKey(City)

class Student(models.Model):
    name = models.CharField(max_length=60)
    roll = models.CharField(max_length=10)
    institute = models.ForeignKey(Institute)

Now I am creating a model form to add/edit students but I provide the option to select city and institute to the user. So basically when a user selects city the corresponding institutes are displayed using JavaScript

# forms.py
class StudentForm(forms.ModelForm):
    city = forms.ModelChoiceField(City)
    institute = forms.ModelChoiceField(queryset=Institute.objects.all())

class Meta:
    model开发者_如何学编程 = Student

But the number of institutes is over 3000. So what I want is to keep the choices as blank initially for institute field (coz they will be filled by the JavaScript once the user selects a City), but upon submitting the data, I get a "Select a valid choice" validation error. Any ideas how to tackle such problem?

Note: When I do NOT specify choices (for institute field) the web page size is 300KB and when I specify them the size of web page is 1.1MB

Apparently, I had to override the Choice widget and change its render method to display no options. Since choices argument is still provided, the validation error does not occur and I can freely use javascript to render institutes by the city selected.

I had the same issue, but overcomed it by setting widget.choices to []

class StudentForm(forms.ModelForm):
    city = forms.ModelChoiceField(City)
    institute = forms.ModelChoiceField(queryset=Institute.objects.all())

def __init__(self, *args, **kwargs):
    super(StudentForm, self).__init__(*args, **kwargs)
    self.fields['institute'].widget.choices = []

You should ensure that the Institute values that get filled up in the select box should also have the primary key as the html id attribute.