I want to remove/replace some properties from list() call on Django rest framework call.
e.g. I have ip_address on the db table, also adds ip_address when perform_create() called, but it should not be shown/included on list() and retrieve() calls.
On retrieve calls, I can make it simply overriding the method then by adding instance.ip_address = None.
But the problem now I have is on list() calls, I need to modify properties of a queryset object.
I tried the following,
o = ThreadedComment.objects.all()
o.annotate(ip_address=Value('', output_field=CharField())).all()
but I got an error:
The annotation 'ip_address' conflicts with a field on the model.
Is there a way to remove/override/replace an properly on queryset in Django? Thanks
As I understood from your question, In one of your views, for the list() and retrive() methods, you want ip_address not to be displayed or not to be in response for any reason. If I understand correctly for this purpose you have many solutions to do one of that is removing the field from the query set by the name of that field:
fields_to_display = [field.name for field in ThreadedComment._meta.get_fields()]
fields_to_display.remove('ip_address')
qs = ThreadedComment.object.all().values(*fields_to_display)
For now I put this workaround. Anyways works for me, but not sure this is the best I could do. Kindly tell me any hints or advices if you have some.
def to_representation(self, instance):
ret = super().to_representation(instance)
if self.context["request"].method == "GET": ret.pop("ip_address")
return ret
Related
I have the following custom model manager in Django that is meant to count the number of related comments and add them to the objects query set:
class PublicationManager(models.Manager):
def with_counts(self):
return self.annotate(
count_comments=Coalesce(models.Count('comment'), 0)
)
Adding this manager to the model does not automatically add the extra field in DRF. In my API view, I found a way to retrieve the count_comments field by overriding the get function such as:
class PublicationDetails(generics.RetrieveUpdateAPIView):
queryset = Publication.objects.with_counts()
...
def get(self, request, pk):
queryset = self.get_queryset()
serializer = self.serializer_class(queryset.get(id=pk))
data = {**serializer.data}
data['count_comments'] = queryset.get(id=pk).count_comments
return Response(data)
This works for a single instance, but when I try to apply this to a paginated list view using pagination_class, overriding the get method seems to remove pagination functionality (i.e. I get a list of results instead of the usual page object with previous, next, etc.). This leads me to believe I'm doing something wrong: should I be adding the custom manager's extra field to the serializer instead? I'm not sure how to proceed given that I'm using a model serializer. Should I be using a basic serializer?
Update
As it turns out, I was using the model manager all wrong. I didn't understand the idea of table-level functionality when what I really wanted was row-level functionality to count the number of comments related to a single instance. I am now using a custom get_paginated_response method with Comment.objects.filter(publication=publication).count().
Original answer
I ended up solving this problem by creating a custom pagination class and overriding the get_paginated_response method.
class PaginationPublication(pagination.PageNumberPagination):
def get_paginated_response(self, data):
for item in data:
publication = Publication.objects.with_counts().get(id=item['id'])
item['count_comments'] = publication.count_comments
return super().get_paginated_response(data)
Not sure it's the most efficient solution, but it works!
In my django website, I have 3 classes: Thing, Category and SubCategory.
Thing has 2 ForeignKeys: "Category" and "SubCategory" (such as Car and Ferrari).
SubCategory has 1 ForeighKey: "Category" (Ferrari is in the category Car)
When I create an instance of Thing in the Admin part and when I choose a Category, I would like that the "SubCategory" field only shows the SubCategories linked to the Category I chose. Is that possible?
I saw the possibility to change the AdminForm like:
class ThingFormAdmin(forms.ModelForm):
def __init__(self,Category,*args,**kwargs):
super (ThingFormAdmin,self ).__init__(*args,**kwargs) # populates the post
self.fields['sub_category'].queryset = SubCategory.objects.filter(category= ... )
But I don't know what to write on the ...
Thanks for the help!
in general always this solution would work:
you need some javascript to catch what has been selected for first selection. then do filtering agin using javascript.
but in django admin, there is autocomplete_fields available. using this would create a kind of selection-input that uses ajax to do some magic filtering on choices when user types some characters. it uses the get_search_results method of the related models admin.ModelAdmin class. overriding that method and giving some extra data to that method could help. but it's the longest way to walk.
Thanks! I will look in the 1st answer after the 2nd, because the fact that I don't have to write JS is very nice, as I am very bad in it.
I manage to use the autocomplete_field to work, but I am stuck with the redefinition of the get_search_results method. If I understood correctly the doc, it will be something like:
def get_search_results(self, request, queryset, search_term):
queryset, use_distinct = super().get_search_results(request, queryset, search_term)
try:
cat = search_term
except ValueError:
queryset |= self.model.objects.all()
else:
queryset |= self.model.objects.filter(category=cat)
return queryset, use_distinct
But I don't understand from where this search_term comes from, and how I can specify it. Any ideas?
https://simpleisbetterthancomplex.com/tutorial/2018/01/29/how-to-implement-dependent-or-chained-dropdown-list-with-django.html
This tutorial will walk you through every step of doing whatever I presume you need to do.
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.
In a Django app, I'm having a model Bet which contains a ManyToMany relation with the User model of Django:
class Bet(models.Model):
...
participants = models.ManyToManyField(User)
User should be able to start new bets using a form. Until now, bets have exactly two participants, one of which is the user who creates the bet himself. That means in the form for the new bet you have to chose exactly one participant. The bet creator is added as participant upon saving of the form data.
I'm using a ModelForm for my NewBetForm:
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
widgets = {
'participants': forms.Select()
}
def save(self, user):
... # save user as participant
Notice the redefined widget for the participants field which makes sure you can only choose one participant.
However, this gives me a validation error:
Enter a list of values.
I'm not really sure where this comes from. If I look at the POST data in the developer tools, it seems to be exactly the same as if I use the default widget and choose only one participant. However, it seems like the to_python() method of the ManyToManyField has its problems with this data. At least there is no User object created if I enable the Select widget.
I know I could work around this problem by excluding the participants field from the form and define it myself but it would be a lot nicer if the ModelForm's capacities could still be used (after all, it's only a widget change). Maybe I could manipulate the passed data in some way if I knew how.
Can anyone tell me what the problem is exactly and if there is a good way to solve it?
Thanks in advance!
Edit
As suggested in the comments: the (relevant) code of the view.
def new_bet(request):
if request.method == 'POST':
form = NewBetForm(request.POST)
if form.is_valid():
form.save(request.user)
... # success message and redirect
else:
form = NewBetForm()
return render(request, 'bets/new.html', {'form': form})
After digging in the Django code, I can answer my own question.
The problem is that Django's ModelForm maps ManyToManyFields in the model to ModelMultipleChoiceFields of the form. This kind of form field expects the widget object to return a sequence from its value_from_datadict() method. The default widget for ModelMultipleChoiceField (which is SelectMultiple) overrides value_from_datadict() to return a list from the user supplied data. But if I use the Select widget, the default value_from_datadict() method of the superclass is used, which simply returns a string. ModelMultipleChoiceField doesn't like that at all, hence the validation error.
To solutions I could think of:
Overriding the value_from_datadict() of Select either via inheritance or some class decorator.
Handling the m2m field manually by creating a new form field and adjusting the save() method of the ModelForm to save its data in the m2m relation.
The seconds solution seems to be less verbose, so that's what I will be going with.
I don't mean to revive a resolved question but I was working a solution like this and thought I would share my code to help others.
In j0ker's answer he lists two methods to get this to work. I used method 1. In which I borrowed the 'value_from_datadict' method from the SelectMultiple widget.
forms.py
from django.utils.datastructures import MultiValueDict, MergeDict
class M2MSelect(forms.Select):
def value_from_datadict(self, data, files, name):
if isinstance(data, (MultiValueDict, MergeDict)):
return data.getlist(name)
return data.get(name, None)
class WindowsSubnetForm(forms.ModelForm):
port_group = forms.ModelMultipleChoiceField(widget=M2MSelect, required=True, queryset=PortGroup.objects.all())
class Meta:
model = Subnet
The problem is that ManyToMany is the wrong data type for this relationship.
In a sense, the bet itself is the many-to-many relationship. It makes no sense to have the participants as a manytomanyfield. What you need is two ForeignKeys, both to User: one for the creator, one for the other user ('acceptor'?)
You can modify the submitted value before (during) validation in Form.clean_field_name. You could use this method to wrap the select's single value in a list.
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
widgets = {
'participants': forms.Select()
}
def save(self, user):
... # save user as participant
def clean_participants(self):
data = self.cleaned_data['participants']
return [data]
I'm actually just guessing what the value proivded by the select looks like, so this might need a bit of tweaking, but I think it will work.
Here are the docs.
Inspired by #Ryan Currah I found this to be working out of the box:
class M2MSelect(forms.SelectMultiple):
def render(self, name, value, attrs=None, choices=()):
rendered = super(M2MSelect, self).render(name, value=value, attrs=attrs, choices=choices)
return rendered.replace(u'multiple="multiple"', u'')
The first one of the many to many is displayed and when saved only the selected value is left.
I found an easyer way to do this inspired by #Ryan Currah:
You just have to override "allow_multiple_selected" attribut from SelectMultiple class
class M2MSelect(forms.SelectMultiple):
allow_multiple_selected = False
class NewBetForm(forms.ModelForm):
class Meta:
model = Bet
participants = forms.ModelMultipleChoiceField(widget=M2MSelect, required=True, queryset=User.objects.all())
I want to save a Django model instance with a ManyToManyField. When I try to do so with the create() manager, it produces the following error:
Exception Value:'post' is an invalid keyword argument for this function
Here is my model:
class Amenity(models.Model):
post=models.ManyToManyField(Post,blank=True,null=True)
name=models.CharField(max_length=50, choices=AMENITIES)
def __unicode__(self):
return str(self.name)
Here is the relevant part of the view:
if request.POST.get('amenities'):
amens=request.POST['amenities'].split(',')
p=int(post.id)
for a in amens:
Amenity.objects.create(post=p,name=a)
return HttpResponse('success')
I'm trying to save multiple amenities at one time and I'd doing so outside of a modelform because I have design in mind and I didn't want to have to create a custom field in this case.
post.id is returning the correct value here, so that doesn't seem to be the issue.
Thanks!
There are two ways you can solve this:
1) By making another database hit: (which is the safest)
p = Post.objects.get(pk=post.id)
if p:
Amenity.objects.create(post=p, name=a)
else:
...
2) Passing the id to post_id
p = int(post.id)
Amenity.objects.create(post_id=p, name=a)
EDIT:
Ok, got it working on my pc. First of all as it is Many to Many, sounds better to use posts not post as a model field. Well anyway this is how you do it:
post = Post.objects.get(pk=id)
for a in amens:
a = Amenity(name=a)
a.post.add(post) #better if it said a.posts.add(post)
a.save()
You might be able to do it via Amenity.objects.create(posts=[p],name=a) since posts expects a list though I haven't tested it myself - all my ManyToMany use a through since they add additional metadata.
You shouldn't pass post.id to post field, cause post is m2m and django take care of it. Where you set post instance ?