participation creation: smart users list

exclude users already participating

accounts/forms.py

@@ -30,6 +30,9 @@ class ParticipationField(forms.ModelChoiceField):
 
 
 class NewParticipationForm(forms.Form):
-
-    participant = ParticipationField(User.objects.all(), widget=Select2Widget(),
+    def __init__(self, *args, **kwargs):
+        site = kwargs.pop('site')
+        super().__init__(*args, **kwargs)
+        queryset = User.objects.exclude(participation__site=site).all()
+        self.fields['participant'] = ParticipationField(queryset, widget=Select2Widget(),
                                      label='Add participant from existing account')

accounts/views.py

@@ -39,7 +39,7 @@ def profile(request):
 @staff_required
 def participation_list(request):
     participation_list = Participation.objects.filter(site=get_current_site(request)).all()
-    form = NewParticipationForm(request.POST or None)
+    form = NewParticipationForm(request.POST or None, site=get_current_site(request))
 
     if request.method == 'POST' and form.is_valid():
         if not Participation.objects.get(user=request.user, site=get_current_site(request)).is_orga():