[FIXED] Populate a Django form field with choices from database (but not from a model)

Issue

I'd like to populate a form dropdown with data from database. Those data don't come directly from a model but from a raw query.

This is working when the database is available and the migrations are already generated. Otherwise, generating the migrations (python manage.py makemigrations myapp) fails because Django evaluates _all_departments() which is not able to find the appropriate table.

def _all_departments() -> List[Tuple[str, str]]:
    from django.db import connection
    with connection.cursor() as cursor:
        cursor.execute("select distinct department from crm_mytable order by department")
        return [(row[0], row[0]) for row in cursor.fetchall()]


class MyForm(forms.Form):
    department = forms.CharField(
        widget=forms.SelectMultiple(choices=_all_departments()))

I naively tried to update manually the choices on __init__ without success (choices are always empty):

class MyForm(forms.Form):
    def __init__(self, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)
        self.fields['department'].widget.choices = _all_departments()

    department = forms.CharField(
        widget=forms.SelectMultiple(choices=[]))

What would be the way to properly fill on-demand the choices?

Solution

You should not pass the choices to the widget, but to the field. You furthermore probably want to use a MultipleChoiceField [Django-doc], this uses a SelectMultiple [Django-doc] as default widget:

class MyForm(forms.Form):

    department = forms.MultipleChoiceField(choices=[])

    def __init__(self, *args, **kwargs):
        super(MyForm, self).__init__(*args, **kwargs)
        self.fields['department'].choices = _all_departments()

Answered By - Willem Van Onsem