How to use choices of a Select field of a form, when defined in the view in Django?

I have an issue with a form with a Select input. This input is used to select a user in a list. The list should only contain user from the group currently used.

I found a solution, however I am not completely sure of what am I doing in the form definition (I do not fully understand how works the def __init__ part). And of course, my code is not working : I obtain the right form, with the choices I need, however if a submit data, it's not saved in the database.

I have been able to check if the form is valid (it is not), the error is the following :

> Category - Select a valid choice. That choice is not one of the available choices.

(I have the same error for the user field). I can't find my way in this, so if you can help, would be very appreciated!

My models:

class Group(models.Model):
    name = models.CharField(max_length=100)
    def __str__(self):
        return self.name   
    
class User(AbstractUser):
    groups = models.ManyToManyField(Group)
    current_group = models.ForeignKey(Group, on_delete=models.SET_NULL,blank = True , null = True, related_name="current_group")

class Category(models.Model):
    name = models.CharField(max_length=100)
    groups = models.ManyToManyField(Group)

    def __str__(self):
        return self.name

class Expanses(models.Model):
    date = models.DateTimeField()
    amount = models.DecimalField(decimal_places=2, max_digits=12)
    category = models.ForeignKey(Category, on_delete=models.CASCADE)
    user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
    group = models.ForeignKey(Group, on_delete=models.CASCADE)
    comment = models.CharField(max_length=500)
    
    def __str__(self):
        return self.amount

My form:

class CreateExpanseForm(forms.ModelForm):
    class Meta:
        model = Expanses
        fields = ['date', 'amount', 'category', 'user','comment']
        widgets={'date':DateInput(attrs={'placeholder':'Date', 'class':'form-input', 'type':'date'}),
                 'amount':TextInput(attrs={'placeholder':'Amount', 'class':'form-input', 'type':'text'}),
                 'category':Select(attrs={'placeholder':'Category', 'class':'form-select', 'type':'text'}),
                 'user':Select(attrs={'placeholder':'user', 'class':'form-select', 'type':'text'}),
                 'comment':TextInput(attrs={'placeholder':'comment', 'class':'form-input', 'type':'text'}),}
    
    def __init__(self, *args, **kwargs):
        user_choices = kwargs.pop('user_choices', None)
        category_choices = kwargs.pop('category_choices', None)
        
        super().__init__(*args, **kwargs)
        if user_choices:
            self.fields['user'].choices = user_choices
        if category_choices:
            self.fields['category'].choices = category_choices   

My view:

def SummaryView(request):
    createExpanseForm = CreateExpanseForm(user_choices = [(user.username, user.username) for user in request.user.current_group.user_set.all()],
                                          category_choices = [(category.name, category.name) for category in request.user.current_group.category_set.all()])
    if request.method == "POST":
        if 'createExpanse' in request.POST:
            createExpanseForm = CreateExpanseForm(user_choices = [(user.username, user.username) for user in request.user.current_group.user_set.all()],
                                                  category_choices = [(category.name, category.name) for category in request.user.current_group.category_set.all()],
                                                  data=request.POST)
            if createExpanseForm.is_valid():
                expanse = createExpanseForm.save()
                if expanse is not None:
                    expanse.group = request.user.current_group
                    expanse.save()
                else:
                    messages.success(request, "Error!")
            
    context = {'createExpanseForm':createExpanseForm}
    return render(request, 'app/summary.html', context)

The form field of a ForeignKey is a ModelChoiceField ^[Django-doc], this neecds the primary key of the item to work with, not the name of a category. You thus try to do too much yourself, and thus invalidated the data of the form field.

I suggest that you let the form handle it and specify the queryset when necessary:

<pre><code>class CreateExpanseForm(forms.ModelForm):
def init(self, *args, user=None, **kwargs):
super().init(*args, **kwargs)
if user is not None:
self.fields['user']<b>.queryset</b> = user.current_group.user_set.all()
self.fields[
'category'
]<b>.queryset</b> = user.current_group.category_set.all()

class Meta:
    model = Expanses
    fields = ['date', 'amount', 'category', 'user', 'comment']
    widgets = {
        'date': DateInput(
            attrs={
                'placeholder': 'Date',
                'class': 'form-input',
                'type': 'date',
            }
        ),
        'amount': TextInput(
            attrs={
                'placeholder': 'Amount',
                'class': 'form-input',
                'type': 'text',
            }
        ),
        'category': Select(
            attrs={
                'placeholder': 'Category',
                'class': 'form-select',
                'type': 'text',
            }
        ),
        'user': Select(
            attrs={
                'placeholder': 'user',
                'class': 'form-select',
                'type': 'text',
            }
        ),
        'comment': TextInput(
            attrs={
                'placeholder': 'comment',
                'class': 'form-input',
                'type': 'text',
            }
        ),
    }</code></pre>

In the view you can then just pass the logged in user:

<pre><code>from django.contrib.auth.decorators import login_required
from django.shortcuts import redirect

@login_required
def summary_view(request):
form = CreateExpanseForm(<b>user=request.user</b>)
if request.method == 'POST':
if 'createExpanse' in request.POST:
form = CreateExpanseForm(
request.POST, request.FILES, <b>user=request.user</b>
)
if form.is_valid():
form<b>.instance.group = request.user.current_group</b>
expanse = createExpanseForm.save()
return redirect('<em>name-of-some-view</em>')

context = {'createExpanseForm': form}
return render(request, 'app/summary.html', context)</code></pre>

> Note: Functions are normally written in snake_case, not PascalCase, therefore it is
> advisable to rename your function to summary_view, not <s>SummaryView</s>.

> Note: You can limit views to a view to authenticated users with the
> @login_required decorator&nbsp;^[Django-doc].

> Note: In case of a successful POST request, you should make a redirect
> ^[Django-doc]
> to implement the Post/Redirect/Get pattern&nbsp;^[wiki].
> This avoids that you make the same POST request when the user refreshes the
> browser.