I'd like to add a dynamic attribute to my serializers whenever they are called. Note that I'm talking about an attribute, not a field. Here's the idea:
User call the API
Viewset calls the serializer with the data
I manage to set self.my_key = my_dynamic_value
Checks and returns the serializer data (normal process)
To set my dynamic value, I need to use self.context meaning I can't override the __init__ method of the serializers (they are called on server start and context is empty)
Any idea on how I could do it?
Using another topic (Pass extra arguments to Serializer Class in Django Rest Framework), I managed to find a suitable solution.
I simply pass my dynamic value within the context by overriding the get_serializer_context method in the view, like that:
class MyViewSet(viewsets.GenericViewSet):
def get_serializer_context(self):
context = super().get_serializer_context()
context["my_key"] = my_value
return context
Then in my serializer, I can get it using self.context["my_key"]
I am using Django detailview. initially, I used the URL pattern
url(r'^todo/details/(?P<pk>[\d]+)', views.todoDetailView.as_view(), name='detail_todo'),
my view is
class todoDetailView(DetailView):
model = models.todo
It worked fine.
In the second case, my URL is
url(r'^todo/details/(?P<id>[\d]+)', views.todoDetailView.as_view(), name='detail_todo'),
this time, I modified my view to
class todoDetailView(DetailView):
model = models.todo
# context_object_name = 'todo_detail'
def get_object(self, **kwargs):
print(kwargs)
return models.todo.objects.get(id=self.kwargs['id'])
It worked fine, I modified the second case to
class todoDetailView(DetailView):
model = models.todo
# context_object_name = 'todo_detail'
def get_queryset(self):
return models.todo.objects.get(id=self.kwargs['id'])
then I get an error,
Generic detail view todoDetailView must be called with either an object pk or a slug.
I know that there is no proper slug or pk provided. So, initially I added get_object() (it worked) but get_queryset() is not working. What is the difference in their working ??
And also if a user is getting details only based on the slug, I read on StackOverflow that
this can be used
slug_field = 'param_name'
slug_url_kwarg = 'param_name'
link - Generic detail view ProfileView must be called with either an object pk or a slug
Can anyone explain me actual working of get_object() and get_queryset() (also get_slug_field() if possible)
Along with the terms slug_field and slug_url_kwarg
Thanks in advance
get_object returns an object (an instance of your model), while get_queryset returns a QuerySet object mapping to a set of potentially multiple instances of your model. In the case of the DetailView (or in fact any class that inherits from the SingleObjectMixin, the purpose of the get_queryset is to restrict the set of objects from which you'll try to fetch your instance.
If you want to show details of an instance, you have to somehow tell Django how to fetch that instance. By default, as the error message indicates, Django calls the get_object method which looks for a pk or slug parameter in the URL. In your first example, where you had pk in the URL, Django managed to fetch your instance automatically, so everything worked fine. In your second example, you overrode the get_object method and manually used the id passed as parameter to fetch the object, which also worked. In the third example, however, you didn't provide a get_object method, so Django executed the default one. SingleObjectMixin's default get_object method didn't find either a pk or a slug, so it failed.
There are multiple ways to fix it:
1. Use pk in the URL
The simplest one is to simply use the code you provided in your first example. I don't know why you were unsatisfied with that, it is perfectly fine. If you're not happy, please explain why in more detail.
2. Override get_object
This is the second solution you provided. It is overkill because if you properly configured your view with the correct options (as you will see in the following alternatives), Django would take care of fetching the object for you.
3. Provide the pk_url_kwarg option
If you really want to use id in the URL for some reason, you can indicate that in your view by specifying the pk_url_kwarg option:
class todoDetailView(DetailView):
model = models.todo
pk_url_kwarg = 'id'
4. Provide the slug_field and slug_url_kwarg options [DON'T DO THIS]
This is a terrible solution because you are not really using a slug, but an id, but it should in theory work. You will basically "fool" Django into using the id field as if it was a slug. I am only mentioning it because you explicitly asked about these options in your question.
class todoDetailView(DetailView):
model = models.todo
slug_field = 'id'
slug_url_kwarg = 'id'
Regarding your get_queryset method: in your example, it doesn't even get to be executed, but in any case it is broken because it returns an individual object instead of a queryset (that's what objects.get does). My guess is you probably don't need a custom get_queryset method at all. This would be useful for example if you had a complex permission system in which different users can only access a different subset of todo objects, which I assume is not your case. Currently, if you provide this get_queryset method, even if everything else is configured properly, you will get an error. Probably an AttributeError saying that the queryset object has no attribute filter (because it will actually be a todo object and not a QuerySet object as Django expects).
The default get_object for DetailView tries to fetch the object using pk or slug from the URL. The simplest thing for you to do is to use (?P<pk>[\d]+) in the URL pattern.
When you override get_object, you are replacing this default behaviour, so you don't get any errors.
When you override get_queryset, Django first runs your get_queryset method an fetches the queryset. It then tries to fetch the object from that queryset using pk or slug, and you get an error because you are not using either of them.
The slug_field and slug_url_kwarg parameters are both defined in the docs. The slug_fields is the name of the field in the model used to fetch the item, and slug_url_kwarg is the name of the parameter in the URL pattern. In your case, you are fetching the object using the primary key (pk/id), so you shouldn't use either of these options.
For your URL pattern with (?P<id>[\d]+), you could use pk_url_kwarg = 'id'. That would tell Django to fetch the object using id from the URL. However, it's much simpler to use your first URL pattern with (?P<pk>[\d]+), then you don't have to override any of the methods/attributes above.
get_object() majorly uses with the generic views which takes pk or id
like: DetailView, UpdateView, DeleteView
where get_queryset() uses with the ListView where we are expecting more objects
Also, get_object() or self.get_object() uses pk as default lookup field or can use slug Field
a little peek at get_object()
if queryset is None:
queryset = self.get_queryset()
# Next, try looking up by primary key.
pk = self.kwargs.get(self.pk_url_kwarg)
slug = self.kwargs.get(self.slug_url_kwarg)
if pk is not None:
queryset = queryset.filter(pk=pk)
# Next, try looking up by slug.
if slug is not None and (pk is None or self.query_pk_and_slug):
slug_field = self.get_slug_field()
queryset = queryset.filter(**{slug_field: slug})
I can't help you with what the error message explicitly means, but get_queryset is used in listviews by get multiple objects, while get_object is used to get a single object (ie DetailView).
If you have a pk you can use to get an object, you don't need to specify a slug field. Slug field are used to filter out objects when you don't have or can't show the primary key publicly. This gives a better explanation of a slug field.
What I Need
I want to have a global configuration for my app and I want to reuse a generic UpdateView.
What I Tried
For this purpose I created a model (example fields):
class Configuration(models.Model):
admin = models.ForeignKey('User', on_delete=models.CASCADE)
hostname = models.CharField(max_length=23)
A generic Updateview:
class ConfigurationView(UpdateView):
model = Configuration
fields = ['admin','hostname']
And urls.py entry
path(
'configuration/',
views.ConfigurationView.as_view(
queryset=Configuration.objects.all().first()
),
name='configuration'
),
As you can see I want the configuration/ path to link to this configuration and always only edit this one object.
Problem
I get the error
AttributeError: 'Configuration' object has no attribute 'all'
Questions
How can I hardcode the object into the path in urls.py so that always the first Configuration object is used for the UpdateView?
Is there a better way to do this? I simply want to have a global configuration object and want it to be editable and displayable with a template of my choice.
You're trying to provide a single object to a class expecting a queryset. The view calls get_queryset which does this;
def get_queryset(self):
"""
Return the `QuerySet` that will be used to look up the object.
This method is called by the default implementation of get_object() and
may not be called if get_object() is overridden.
"""
if self.queryset is None:
if self.model:
return self.model._default_manager.all()
else:
raise ImproperlyConfigured(
"%(cls)s is missing a QuerySet. Define "
"%(cls)s.model, %(cls)s.queryset, or override "
"%(cls)s.get_queryset()." % {
'cls': self.__class__.__name__
}
)
return self.queryset.all()
You've provided a queryset so that lands on self.queryset.all() which for your example is calling all() on an instance of your class.
To use the queryset kwarg of as_view() you'd do something like MyView.as_view(queryset=MyModel.objects.filter(enabled=True))
So you need to change the way the view looks for the object;
class ConfigurationView(UpdateView):
def get_object(self):
return Configuration.objects.first()
By default UpdateView does this to get an object; https://ccbv.co.uk/projects/Django/2.0/django.views.generic.edit/UpdateView/
If you're limiting the config to 1 object you will also want to implement a Singleton design. Essentially this is a way to ensure only 1 object can exist. Read more here; https://steelkiwi.com/blog/practical-application-singleton-design-pattern/
There is a really helpful package for singletons called django-solo
views.py
def retrieve(self, request, weather_date=None):
as shows in the image of retrieve() i have change the argument as weather_date but the swagger is generating only pk and serializer class is viewsets.ReadOnlyModelViewSet and the router in urls.py is DefaultRouter.
Rest-swagger introspects the the ModelViewSet class rather than the function signature. That field is based off the lookup_field attribute on view class. Reason being is that object lookups are also used for update, partial update and delete
ie
delete /api/weather/air-pollution/:weather_date
or
patch /api/weather/air-polution/:weather_date
The lookup field on this is defaulted to 'id'. Instead I would over ride the value in your Weather viewset class.
class Weather(viewsets.ReadOnlyModelViewSet):
lookup_field = 'weather_date'
Changing this should reflect in your rest swagger docs
class User(generics.RetrieveAPIView):
serializer_class = RetrieveLocalSerializer
queryset = User.objects.filter(
fields_1=True,
fields_2=False
)
class LocalSerializer(serializers.ModelSerializer):
class Meta:
model = User
fields = ('field_1', 'field_2', 'field_3',)
The API did not work as it I wish. When I tried get user that does not have the property i want, it still returned the result.
I even tried override that function but it did not work too.
def get_queryset(self):
return User.objects.filter(
is_localguide=True,
state=PROFILE_STATE.PUBLISHED
)
Any help is appreciated.
If I understood your question correctly you wish to get list of instances in your view (using Django Rest Framework). The problem is that your view is inheriting from a generics.RetrieveAPIView. This view class calls self.retrieve(request, *args, **kwargs) method which returns you an object, not queryset. I think that you should inherit your view from a ListAPIView class. This class inherits ListModelMixin which
Provides a .list(request, *args, **kwargs) method, that implements listing a queryset.
So your code will be looking like this:
class User(generics.ListAPIView):
serializer_class = RetrieveLocalSerializer
queryset = User.objects.filter(
fields_1=True,
fields_2=False
)
See http://www.django-rest-framework.org/api-guide/generic-views/#listapiview for more information.
You may either define your queryset in a view or override get_queryset method:
queryset - The queryset that should be used for returning objects from this view. Typically, you must either set this attribute, or override the get_queryset() method. If you are overriding a view method, it is important that you call get_queryset() instead of accessing this property directly, as queryset will get evaluated once, and those results will be cached for all subsequent requests.
You may find more information here: http://www.django-rest-framework.org/api-guide/generic-views/#genericapiview
Hope this will help)