Dynamically specify a ModelChoiceField queryset in Django

Introduction

There is a case where you want to control the items that can be selected according to the authority of the logged-in user for the list box that is referenced by the master.

↓ A memo of how to investigate and try using the model and form as a sample.

models.py

class Book(models.Model):
    name = models.charField('name',max_length=255)

forms.py

class SampleForm(forms.Form):
    book = forms.ModelChoiceField(label='book',queryset=Book.objects.all())

Overwrite queryset after form generation

Probably the simplest way.

python

form = SampleForm()
form.fields['book'].queryset = Book.objects.filter(...)

Receive queryset as an argument and overwrite it with __init__ of the form

forms.py

class SampleForm(forms.Form):
    book = forms.ModelChoiceField(label='book',queryset=Book.objects.none())
    def __init__(self, queryset=None, *args, **kwargs):
        super(SampleForm,self).__init__(*args,**kwargs)
        if queryset :
            self.fields['book'].queryset = queryset

python

form = SampleForm(queryset=Book.objects.filter(...))

Note that self.fields will not be generated unless you call super.__ init__.

What to do with the default queryset depends on the role of the form.

It is also possible to implement that the queryset itself is not received, only the data used for the filter condition is received, and the queryset is generated on the form side.

forms.py

class SampleForm(forms.Form):
    book = forms.ModelChoiceField(label='book',queryset=Book.objects.none())
    def __init__(self, permission=None, *args, **kwargs):
        super(SampleForm,self).__init__(*args,**kwargs)
        self.fields['book'].queryset = self.get_book_list(permission)

    def get_book_list(self, permission=None):
        if not permission :
            return Book.objects.none()

        if permission == AAA :
            query = Q(...)
        elif permission == BBB :
            query = Q(...)
        #Write as much as you need...

        return Book.objects.filter(query)

What you are doing is essentially the same. The point is that you can overwrite Form.fields ['field_name']. Queryset after processing Form.__ init__.

Digression

By playing with Form.fields, you can change various attributes of other fields after the form is created. Is it possible to add / remove the field itself?