Modelserializer using kwargs to get FK object - django

Question

I'm creating a Django (1.8) webapp that saves racing laptimes and scoreboards. The database is populated using an API built using Django Rest Framework. It's the first time I'm trying to build a proper api using rest framework.
A quick overview of the models:
Event, A racing event/weekend
Session, A single race/practice/quali - FK Event
Car, A car taking part in a session - FK Session
Lap, Laps for specific car - FK Car
The Event is created manually, but the rest is supposed to be "dynamic" (get or create)
Right now I'm trying to create a new car using my API, but I'm stuck. To get the cars event and session I'm trying to use the url;
/api/results/skrotbilsracet-29042016/r1/cars/
The idea is to post data to this url and "get or create" a new car object.
To get the correct session object for the new car session FK, I need to use a custom function that takes the kwargs and tries to find the session.
The more I read about how to solve this, the more confused I get.
Could someone push me in the right direction?
This is my latest attempt at solving this, which just gives me "{"session":["This field is required."]}"
models.py
class Session(models.Model):
session_types = (
('p', 'Practice'),
('q', 'Qualification'),
('r', 'Race')
)
event_id = models.ForeignKey(Event, related_name='sessions')
name = models.CharField(max_length=2, blank=True)
current_session = models.BooleanField(default=True)
session_type = models.CharField(max_length=2,
choices=session_types)
started = models.DateTimeField(auto_now_add=True)
ended = models.DateTimeField(auto_now=True)
class Meta:
ordering = ['started']
def save(self):
if not self.name:
# Get number of sessions
session_count = Session.objects.filter(event_id=self.event_id)\
.filter(session_type=self.session_type)\
.count()
session_count += 1
self.name = self.session_type + str(session_count)
super(Session, self).save()
def __unicode__(self):
string = self.started.strftime("%d-%m-%Y %H:%M") + ' - '
string += self.name.upper()
return(string)
class Car(models.Model):
session = models.ForeignKey(Session, related_name='cars')
number = models.IntegerField()
full_name = models.CharField(max_length=256, blank=True)
short_name = models.CharField(max_length=256, blank=True)
race_class = models.CharField(max_length=50, blank=True)
best_lap = models.IntegerField(blank=True, null=True)
best_lap_time = models.CharField(max_length=20, blank=True)
best_sector1 = models.CharField(max_length=20, blank=True)
best_sector2 = models.CharField(max_length=20, blank=True)
best_sector3 = models.CharField(max_length=20, blank=True)
best_speed = models.IntegerField(blank=True, null=True)
pitstops = models.IntegerField(blank=True, null=True)
total_time = models.CharField(max_length=20, blank=True)
transponder = models.CharField(max_length=50, blank=True)
apiUrls.py
urlpatterns = [
url(r'^raceslug/$', raceSlugView.as_view(), name='race-slug'),
url(r'^events/$', eventsView.as_view(), name='event-list'),
url(r'^session/$', getSessionView.as_view(), name='session-pk'),
url(r'^(?P<event_id>[a-z0-9\-]+)/$', eventView.as_view(), name='event-detail'),
url(r'^(?P<event_id>[a-z0-9\-]+)/(?P<name>[a-z0-9\-]+)/$', sessionView.as_view(), name='session-detail'),
url(r'^(?P<event_id>[a-z0-9\-]+)/(?P<name>[a-z0-9\-]+)/cars/$', carsView.as_view(), name='car-list'),
url(r'^(?P<event_id>[a-z0-9\-]+)/(?P<name>[a-z0-9\-]+)/(?P<number>[0-9]+)/$', carView.as_view(), name='car-detail'),
]
urlpatterns = format_suffix_patterns(urlpatterns)
api.py
class carsView(generics.ListCreateAPIView):
serializer_class = carSerializer
def get_session(self, event_id, name):
print('Getting session')
# Get event object
try:
event = Event.objects.get(event_id=event_id)
print('Found event')
except ObjectDoesNotExist:
print('Did not find event')
return
# Get session object
try:
session = event.sessions.get(name=name)
print('Found session: ', session)
return session
except ObjectDoesNotExist:
print('Did not find session')
return
def get_queryset(self):
print('Getting queryset')
print('event_id: ' + self.kwargs['event_id'])
print('name: ' + self.kwargs['name'])
session = self.get_session(self.kwargs['event_id'], self.kwargs['name'])
return(Car.objects.filter(session=session.pk))
def perform_create(self, serializer):
print('Creating new car')
session = self.get_session(self.kwargs['event_id'], self.kwargs['name'])
serializer.save(session=session)
serializers.py
class carSerializer(serializers.ModelSerializer):
laps = lapSerializer(many=True, read_only=True)
class Meta:
model = Car
fields = (
'session',
'number',
'full_name',
'short_name',
'race_class',
'best_lap',
'best_lap_time',
'best_sector1',
'best_sector2',
'best_sector3',
'best_speed',
'pitstops',
'total_time',
'transponder',
'laps')
Solution:
This is what I actually changed to get it working.
api.py
from rest_framework.serializers import ValidationError
class carsView(generics.ListCreateAPIView):
...
def perform_create(self, serializer):
print('Creating new car')
session = self.get_session(self.kwargs['event_id'], self.kwargs['name'])
number = self.request.POST.get('number')
car = session.cars.filter(number=number)
if car.exists():
raise ValidationError('Car already exists')
serializer.save(session=session)
serializers.py
class carSerializer(serializers.ModelSerializer):
laps = lapSerializer(many=True, read_only=True)
session = serializers.StringRelatedField(required=False)
...

Answer 1

I see that you're creating your session ID there:
def get_queryset(self):
...
session = self.get_session(self.kwargs['event_id'], self.kwargs['name'])
return(Car.objects.filter(session=session.pk))
Then you don't need it in a serializer, only in a model. So you can set it a snot required in a serializer, but it will still be required in a model.
I guess this answer could help you: Django REST Framework serializer field required=false