Question

I need to pass an instance variable (self.rank) to be used by a class variable (provider) (see the commented out line below).

Commented out, the code below works. But I’m pretty sure I shouldn’t be trying to pass an instance variable up to a class variable anyway. So I’m dumbfounded as to how to accomplish my goal, which is to dynamically filter down my data in the ModelChoiceField.

As you can see, I already overrided ModelChoiceField so I could beautify the usernames. And I also subclassed my basic SwapForm because I have several other forms I’m using (not shown here).

Another way of saying what I need … I want the value of request.user in my Form so I can then determine the rank of that user and then filter out my Users by rank to build a smaller ModelChoiceField (that looks good too). Note that in my views.py, I call the form using:

form = NewSwapForm(request.user)

or

form = NewSwapForm(request.user, request.POST)

In forms.py:

from myapp.swaps.models import Swaps
from django.contrib.auth.models import User

class UserModelChoiceField(forms.ModelChoiceField):
    """ Override the ModelChoiceField to display friendlier name """
    def label_from_instance(self, obj):
    return "%s" % (obj.get_full_name())

class SwapForm(forms.ModelForm):
    """ Basic form from Swaps model. See inherited models below. """
    class Meta:
        model = Swaps

class NewSwapForm(SwapForm):
    # Using a custom argument 'user'
    def __init__(self, user, *args, **kwargs):
        super(NewSwapForm, self).__init__(*args, **kwargs)
        self.rank = User.objects.get(id=user.id).firefighter_rank_set.get().rank

    provider = UserModelChoiceField(User.objects.all().
            order_by('last_name').
            filter(firefighter__hirestatus='active')
            ### .filter(firefighter_rank__rank=self.rank)  ###
            )

    class Meta(SwapForm.Meta):
        model = Swaps
        fields = ['provider', 'date_swapped', 'swap_shift']

Thanks!

Answer 1

You can’t do it that way, because self doesn’t exist at that point – and even if you could, that would be executed at define time, so the rank would be static for all instantiations of the form.

Instead, do it in __init__:

provider = UserModelChoiceField(User.objects.none())

 def __init__(self, user, *args, **kwargs):
    super(NewSwapForm, self).__init__(*args, **kwargs)
    rank = User.objects.get(id=user.id).firefighter_rank_set.get().rank # ??
    self.fields['provider'].queryset = User.objects.order_by('last_name').filter(
           firefighter__hirestatus='active', firefighter_rank__rank=rank)

I’ve put a question mark next to the rank line, because rank_set.get() isn’t valid… not sure what you meant there.