Django REST Framework customize update method

Question

My application has the following structure:

models.py

class EventHost(models.Model):

    hostid = models.ForeignKey(Host, on_delete=models.PROTECT)
    eventid = models.ForeignKey(Event, on_delete=models.CASCADE)
    someparam = models.CharField(max_length=100, blank=True, null=True)

    ...

    class Meta:
        unique_together = ("hostid", "event")


class Host(models.Model):
    hostid = models.IntegerField(primary_key=True)
    hostname = models.CharField(max_length=100)
    ...


class Event(models.Model):
    eventid = models.AutoField(primary_key=True)
    eventname = models.CharField(max_length=100)
    ...
    hosts = models.ManyToManyField(Host, through='EventHost')

views.py

class EventViewSet(viewsets.ModelViewSet):
    queryset = Event.objects.order_by('-date')
    serializer_class = EventSerializer

class HostViewSet(viewsets.ModelViewSet):
    queryset = Host.objects.order_by('-hostid')
    serializer_class = HostSerializer

class EventHostViewSet(viewsets.ModelViewSet):
    queryset = EventHost.objects.all()
    serializer_class = EventHostSerializer

Currently to update EventHost table I'm doing http put providing id (which is primary key) in my url .

I'd like to be able to update EventHost providing hostname and eventname (which will be passed in url) instead of id.

Using SQL it would look like this:

update eventhost set someparam='somevalue' from eventhost as a, event as b, host as c where b.id = a.eventid and c.hostid = a.hostid and b.eventname='myevent' and c.hostname='myhost';

From documentation I understood that I would need to modify the default update method for the viewset or/and modify queryset. Any ideas how should it be achieved?

kamilyrb · Accepted Answer · 2020-05-18 16:36:11Z

1

You can override get_object method and use your parameters provided from url like that:

class EventHostViewSet(viewsets.ModelViewSet):
    queryset = EventHost.objects.all()
    serializer_class = EventHostSerializer

    def get_object(self):
       return EventHost.objects.get(hostid=self.kwargs['hostid'],eventid=self.kwargs['eventid'])

In this way, you must manage if there is no record with this query scenario, as custom

answered May 18, 2020 at 16:36

kamilyrb

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Comments

mon io · Accepted Answer · 2020-05-19 17:41:41Z

1

Assuming that you have properly constructed URL.

Edited EventHostViewSet.get_object method:

class EventHostViewSet(viewsets.ModelViewSet):
    ...
    lookup_field = 'eventname'
    def get_object(self):
        queryset = self.filter_queryset(self.get_queryset())

        filter_kwargs = {'hostid__hostname': self.kwargs.get('hostname'),
                         'eventid__eventname': self.kwargs.get('eventname')}
        obj = get_object_or_404(queryset, **filter_kwargs)

        self.check_object_permissions(self.request, obj)
        return obj

EventHostViewSet registration:

router.register(rf'event-hosts/(?P<hostname>[.]+)', EventViewSet)

Some comments about your problem:

You will have problem when in your system will exist two EventHost with same hostid__hostname and eventid__event because queryset get method should only return ONE record
in DRF PUT method needs all fields to be provided in request data, if you want to update selected fields you should use PATCH method or override update viewset method (set partial to True)

EDITED AGAIN:

This is really bad design, you should not do this like that (somehow you should use id / maybe @action decorator to construct specific url for updating like that).

edited May 19, 2020 at 17:41

answered May 18, 2020 at 18:33

mon io

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4 Comments

pitmod Over a year ago

Thanks. How should I construct it in urls.py? Currently it looks like this:

router = routers.DefaultRouter() router.register(r'accounts', AccountViewSet) router.register(r'events', EventViewSet) router.register(r'hosts', HostViewSet)                                                                                          urlpatterns = [      url(r'^api/v1/', include(router.urls)),  ]

Can I use some regex in route.register?

mon io Over a year ago

I edited answer again. This is really bad design (but it resolves your problem - workaround) and you should use diffrent solution.

pitmod Over a year ago

Could you give me an example of url that should be used here? I'm still struggling to make it work

mon io Over a year ago

.../event-hosts/SOMEHOSTNAME/SOMEEVENTNAME

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