"Simple Dynamic" Dropdown menu in django form

Question

First, I am quite new with django... I am trying to add a dropdown menu of available distinct Users (by name and coming from my db "dynamically") in a form.

I am using django 2.2.6.

# MyCustomForm
class DetailedReportForm(forms.Form):
    AVAILABLE_USERS = MyUserModel.objects.order_by().values_list('name').distinct()
    selected_date = forms.DateTimeField(input_formats=['%d/%m/%Y'], required=True, widget=DateInput())
    selected_user = forms.CharField(label="Select a user", widget=forms.Select(choices=AVAILABLE_USERS))

# MyModel
class MyUserModel(models.Model):
    id = models.AutoField(db_column='Id', primary_key=True)
    name = models.CharField(db_column='Name', unique=True, max_length=90)
    ...
    def __str__(self):
        return str(self.name)

The issue I am facing is my queryset is not working (not sure why) as it is giving me the following: not enough values to unpack (expected 2, got 1)

I tried to google it but still not very clear to me what this error message means.

Can someone please explain what this django error means so I can fix it and include the dropdown list in my form?

neverwalkaloner · Accepted Answer · 2020-02-10 17:39:45Z

3

The problem is choices argument expecting list of tuples like this: [(1, "one"), (2, "two")]. First element in tuple actual value to store in DB, second is human readable representation.

But actually in your case you can just use ModelChoiceField instead:

class DetailedReportForm(forms.Form):
    AVAILABLE_USERS = MyUserModel.objects.order_by().values_list('name').distinct()
    selected_date = forms.DateTimeField(input_formats=['%d/%m/%Y'], required=True, widget=DateInput())
    selected_user = forms.ModelChoiceField(label="Select a user", queryset=MyUserModel.objects.order_by().distinct("name"))

Otherwise list of available options wiil not updated dynamically, since code inside form class running only once on django starting.

answered Feb 10, 2020 at 17:39

neverwalkaloner

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2 Comments

WilliamW Over a year ago

Thank you for your answer, for some reason. I cannot distinct on field when the backend is MySQL. So I had to replace your dictinct("name") to be distinct() here

neverwalkaloner Over a year ago

@WilliamW yep, unfortunatelly distinct by field only work on PostgreSQL now.

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