Btukfyl

I'm building a form for user's to run a query on a database. The model is called Sample and the user is selecting the names they want to include in the query results. In this case the name field is unique but other fields done the same way aren't.

Form.py

from django import forms

from .models import Sample



class SampleForm(forms.Form):

    samples = Sample.objects.all()

    names = [(s.id, s.name) for s in samples]

    initial = [c[0] for c in names]

    Rock_Names = forms.MultipleChoiceField(widget=forms.CheckboxSelectMultiple,

                                          choices=names,

                                          initial=initial,

                                          label='Name')

The problem I'm having is when a new sample has been added the form won't update with that sample name until I restart the server. I have a list view for all samples and it updates with the new sample fine. I've tried running Sample.objects.update() after the new sample is saved, but that didn't help. Is there a way to force this to update? Is there a better way to build a query form?

Edit Okay, I thought through this and realized it is a more basic object oriented programming problem. The form is created using class attributes defined with the class definition (at server restart) and not when an instance is created (when the page reloads). I don't think I want to rerun the form creation every time the page loads (such as moving to instance attributes in an init method), so I moved the form creation to a function that is called at class definition and through a method I can call when I add data. The new code looks like:

from django import forms

from .models import Sample



def create_form():

    samples = Sample.objects.all()

    names = [(s.id, s.name) for s in samples]

    initial = [c[0] for c in names]

    Rock_Names = forms.MultipleChoiceField(widget=forms.CheckboxSelectMultiple,

                                          choices=names,

                                          initial=initial,

                                          label='Name')

    return Rock_Names



class SampleForm(forms.Form):

    Rock_Names = create_form()



   def update_form():

      Rock_Names = create_form()

When you have a choice field with dynamic choices, setting them in the __init__ method is the recommended approach.

In your case, you can probably simply use a ModelMultipleChoiceField instead of a MultipleChoiceField:

class SampleForm(forms.Form):



    rock_names = forms.MultipleChoiceField(widget=forms.CheckboxSelectMultiple,

                                          queryset=Sample.objects.all(),

                                          label='Name')

To get Sample.name as label, you either have to give Sample a __str__ method:

class Sample(models.Model):



    ...



    def __str__(self):

        return self.name

Or create and use a subclass of ModelMultipleChoiceField with a custom label_from_instance method:

class SampleMultipleChoiceField(MultipleChoiceField):



    def label_from_instance(self, obj):

        return obj.name





class SampleForm(forms.Form):



    rock_names = SampleMultipleChoiceField(widget=forms.CheckboxSelectMultiple,

                                          queryset=Sample.objects.all(),

                                          label='Name')

On a side note, the common convention is to write class attributes in lower case.