reduce sql request count

zitap/views.py

@@ -60,14 +60,17 @@ def create_event(request):
 @vary_on_cookie
 def event(request, url):
     try:
-        event = Event.objects.prefetch_related('date_set', 'participant_set', 'participant_set__user').get(url=url)
+        participants = list(Participant.objects.prefetch_related('user', 'event', 'event__date_set').filter(event__url=url))
+        event = participants[0].event
     except Event.DoesNotExist:
         return render(request, 'zitap/event-not-found.html')
     
     # Check if the user is logged in
     if 'user_id' in request.session:
-        participant = event.participant_set.filter(user_id=request.session['user_id']).first()
-        if participant is None:
+        for participant in participants:
+            if participant.user_id == request.session['user_id']:
+                break
+        else:
             participant, created = Participant.objects.get_or_create(user_id=request.session['user_id'], event=event)
         login_form = None
         update_form = UpdateSlotsForm(initial={'slots': slots2string(participant, get_slot_count(event))}, participant=participant)
@@ -77,7 +80,7 @@ def event(request, url):
     return render(
         request, 
         'zitap/event.html', 
-        {'event': event, 'grid': slots2grid(event, list(event.participant_set.all()), False), 'login_form': login_form, 'update_form': update_form}
+        {'event': event, 'grid': slots2grid(event, participants, False), 'login_form': login_form, 'update_form': update_form}
     )
 
 def login(request, url):
@@ -164,12 +167,15 @@ def slots_api(request, url):
     The string begins with the first slot of the first day of the event and ends with the last slot of the last day of the event.
     """
     try:
-        event = Event.objects.get(url=url)
+        participants = Participant.objects.select_related('event', 'user').filter(event__url=url)
+        event = participants.first().event
         slot_count = get_slot_count(event)
 
         # Check if the user is logged in and wants to update their slots
         if 'user_id' in request.session and request.method == 'POST':
-            participant = Participant.objects.get(user_id=request.session['user_id'], event=event)
+            participant = participants.filter(user_id=request.session['user_id']).first()
+            if participant is None:
+                participant = Participant.objects.get_or_create(user_id=request.session['user_id'], event=event)
             form = UpdateSlotsForm(request.POST, participant=participant)
             if form.is_valid():
                 data = form.cleaned_data
@@ -178,7 +184,6 @@ def slots_api(request, url):
 
         # Get the slots of each participant
         data = {}
-        participants = event.participant_set.all()
         for participant in participants:
             data[participant.user.username] = slots2string(participant, slot_count)