I have a function in DRF where I want to tell the system to update "everybody", say I want to give everyone that logged in today a free prize and want to persist that list (I get this example is dumb, it just me trying to generalize my use case). It will query to see which users have signed in today and then I want to loop through those users to create a new activity of giving them a prize.
It appears to only be storing the last value in the loop on write.
time_threshold = datetime.now() - timedelta(hours=12)
signed_in_list = Activity.objects.filter(created__gte=time_threshold, activity="signed in")
for activity in signed_in_list:
serializer.save(user=activity.user_id, activity="gets free prize")
headers = self.get_success_headers(serializer.data)
return Response(serializer.data, status=status.HTTP_201_CREATED,
headers=headers)
I'm trying to get it so that each user ID that is returned from the "signed_in_list" would have a new activity written.
I was expecting a new Activity entry to be written for each user_id in the loop, but it only is executing the last user_id in the loop. That makes me think the serializer.save is working, but overriding itself each time in the loop (versus performing the write to the DB).
You refer to "for user in" and "user.id" when in fact it's not a user, those objects you are referring to are activities.
Ideally I'd like to see your serializer, but given you have passed the same argument as the queryset command I assume the Serializer's model is Activity?
In which case you are attempting to save a new activity with the same primary key id as a previous existing activity which was returned in your queryset. This is an update, but to run an update on a serializer, the Activity instance would need to be passed to the serializer when it was initialized. In general, whether with Django models or DRF serializers, you never need to pass the id to save, especially not an existing id.
Assuming you have a foreign key on the activity model called "user" which references the User model you can do:
time_threshold = datetime.now() - timedelta(hours=12)
signed_in_list = Activity.objects.filter(created__gte=time_threshold, activity="signed in")
for activity in signed_in_list:
serializer.save(user=activity.user, activity="gets free prize")
headers = self.get_success_headers(serializer.data)
return Response(serializer.data, status=status.HTTP_201_CREATED,
headers=headers)
Regarding "user=activity.user", passed as a keyword argument to serializer.save(), this is the way you would do it when saving a model. I think it's the same with DRF serializers, I'm not 100% sure but if it doesn't work you can try user=activity.user.id
I was able to resolve this. Rather than serializer.save, I updated the request and recursively called my create function
def create(self, request, *args, **kwargs):
time_threshold = datetime.now() - timedelta(hours=12)
signed_in_list = Activity.objects.filter(created__gte=time_threshold, activity="signed in")
for activity in signed_in_list:
request.data["user"] = activity.user
self.create(request, *args, **kwargs)
return Response(status=status.HTTP_201_CREATED)
Related
I want to create a user at the creation of an object. This object is linked to the user by a foreign key.
I have override the def_save() method to create the user and link it to the object.
Problem: I generate a random password for this user and I would like to send it by e-mail not to the just created user but to the user.
def save(self, *args, **kwargs):
if self._state.adding:
super(Machine, self).save(*args, **kwargs)
username = f"machine_{slugify(self.site.client.name).lower()}_{self.id}"
password = User.objects.make_random_password()
self.user = User.objects.create(
username=username,
password=password
)
self.save(update_fields=['user'])
send_mail(
f'Password of {username}',
f'Password: {password}',
settings.DEFAULT_FROM_EMAIL,
[self.request.user.email],
fail_silently=True,
)
else:
super(Machine, self).save(*args, **kwargs)
The problem is that I don't have access to self.request in this method.
How can I access to request in my def save()?
Or how can I get the password value in my view?
I think you should design this differently.
If there is always a view, it suggests that the only legitimate place this object and the related user could be created is inside a particular view. So, use get_or_create and if it was created, then invoke the logic to create and associate the new user and e-mail the password to the current Django user.
You could harden it against object creation outside of an appropriate view by instead using
try:
existing_instance = MyModel.objects.get( ...)
except MyModel.DoesNotExist
new = MyModel( ...)
# create and associate the User object here
setattr( new, '_foo_bar', 'not_Molly') # a Mollyguard
new.save()
and check in MyModel's save method that self._foo_bar is present and correct. Raise a meaningful error if not. This will avoid accidental creation of MyModel instances without an associated User by, say, newly recruited help who don't fully understand the bad implications of doing this.
If you really, really want, you could pass the current request.User as the value of an attribute, and check isinstance( self._foo_bar, User) and then having crashed out if you don't have a valid User, put the logic in the save method. This feels wrong to me.
To answer your question directly (I definitely think you should read the design suggestions here also) but to get the request object throughout the request cycle, one solution is threadlocals. Threadlocals middleware puts the request object on a thread-accessible storage, and then provides a get_current_request handler that you can import anywhere and grab the request off of local storage.
So many caveats here: Django core devs intentionally didn't include this functionality, here is a great discussion of why you shouldn't do this, Python is not 100% thread safe, this may be (and probably is) an anti-pattern, and consider the cases brought up in this thread.
I'm trying to create a fully anonymous survey, where the survey participant enters a landing site (index.html), clicks a link and is directed to a survey view. On this survey (pre_test.html) page, I want to assign a new Participant object with a primary key and link that to the Survey model via a foreign key. Because this Survey isn't the main part of my study, I want to send that Participant object to a new view, where the Participant primary key is again used as a foreign key to link to another model (call it Task).
What I've tried so far in the views.py is:
def pre_test(request):
if request.method == "POST":
participant = Participants()
participant.save()
participant_pk = participant.pk
form = PreTestQuestionnaireForm(request.POST)
if form.is_valid():
post = form.save(commit=False)
post.save()
post_primary = PreTestQuestionnaire(pk=post.pk)
post_primary.Analyst_id = Participants(pk=participant_pk)
post_primary.save()
request.session['user'] = participant_pk
return HttpResponseRedirect(reverse('main:picture_test'))
else:
form = PreTestQuestionnaireForm()
return render(request, 'study/pre_test.html', {'form': form})
def picture_test(request):
obj = Participants(Unique_ID=request.session.get('user')) # Unique_ID is the pk I've set for Participants
but when calling print(obj) all I get is Participants object (None). What am I missing in using the session? Should I not be using sessions in this way at all, or should I create actual users in another table without giving them passwords and other data? Keeping the users anonymous is essential and I want to avoid cookies as much as possible, although I can write code to remove cookies after each session.
I believe I have found the culprit.
I had set SESSION_COOKIE_SECURE=True in the settings.py file, which blocks cookies from working well in localhost development and thus using request.session.get() doesn't return anything.
I have a view that I'm using for GET and POST to a database that's NOT the default DB.
class DeployResourceFilterView(generics.ListAPIView):
serializer_class = ResourceSerializer
def get(self, request, format=None):
resname = self.request.GET.get('name')
queryset = Resmst.objects.db_manager('Admiral').filter(resmst_name=resname)
serializer = ResourceSerializer(queryset)
if queryset:
return Response(serializer.data)
else:
raise Http404
def post(self, request, format=None):
serializer = ResourceSerializer(data=request.DATA, many=True)
if serializer.is_valid():
serializer.save()
return Response(serializer.data, status=status.HTTP_201_CREATED)
return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
The GET works perfectly fine but on the POST it constantly fails complaining that the table does not exist. My assumption is that the reason for this is because it's trying to use the default database not the 'Admiral' one I have defined as my secondary database. How do I assign the POST to use a specific database and not the default?
See this link to the docs: https://docs.djangoproject.com/en/1.7/topics/db/multi-db/#selecting-a-database-for-save
You can specify the database you want to save to, just pass it as a parameter:
my_object.save(using='database-name')
In your case it would be:
serializer.save(using='Admiral')
You should also use it in your queryset like this:
queryset = Resmst.objects.using('Admiral').filter(resmst_name=resname)
Since it is a queryset and not a command that needs a db_manager as creating objects is.
In the code provide by the op, the issue arises when serializer is trying to be saved, i.e. on the line
serializer.save()
-the default database is being used. One cannot use the form serializer.save(using='database_name') as the accepted answer recommends, because the kwarg "using='database_name" will not be understood/expected by a serializer class (in this case the class ResourceSerializer).
The django docs state that if you have a model (model.Model) then yes you can save using
my_object.save(using='database_name') see here for the quote: https://docs.djangoproject.com/en/2.1/topics/db/multi-db/#selecting-a-database-for-save
. But serializer is obviously not a model instance.
In such a case as above, you could subclass (or amend -I prefer amending when I have created the serializer myself) ResourceSerializer and change the create and update methods to work utilizing db_manager('Admiral'). For example:
class MyResourceSerializer(ResourceSerializer):
def create(self, validated_data):
"""
copy the create from ResourceSerializer and amend it here, with code such as
follows in the try section.
"""
ModelClass=Resmst # or whichever desired model you are acting on
try:
instance = ModelClass.objects.db_manager('Admiral').create(**validated_data)
except TypeError: # or whatever error type you are mitigating against, if any
raise TypeError()
return instance
A nice alternative (as elim mentions in one of the comments to this question) is to add a router and have this all handled without having to insert "using" or "db_manager" throughout the code: https://docs.djangoproject.com/en/2.1/topics/db/multi-db/#using-routers
Say for example you're using a ListCreateAPIView
You might might be able to do it at the view level, using get_queryset
When to use get, get_queryset, get_context_data in Django?
class YourModelDRFGetView(generics.ListCreateAPIView):
serializer_class = YourModelDRFViewSerializer
def get_queryset(self):
return YourModel.objects.using('your_read_replica').all()
Where your_read_replica is defined in settings.py:
replica_database_url = os.environ.get("DATABASE_REPLICA_URL") or database_url
DATABASES["your_read_replica"] = dj_database_url.parse(replica_database_url)
When I try to deserialize some data into an object, if I include a field that is unique and give it a value that is already assigned to an object in the database, I get a key constraint error. This makes sense, as it is trying to create an object with a unique value that is already in use.
Is there a way to have a get_or_create type of functionality for a ModelSerializer? I want to be able to give the Serializer some data, and if an object exists that has the given unique field, then just return that object.
In my experience nmgeek's solution won't work in DRF 3+ as serializer.is_valid() correctly honors the model's unique_together constraint. You can work around this by removing the UniqueTogetherValidator and overriding your serializer's create method.
class MyModelSerializer(serializers.ModelSerializer):
def run_validators(self, value):
for validator in self.validators:
if isinstance(validator, validators.UniqueTogetherValidator):
self.validators.remove(validator)
super(MyModelSerializer, self).run_validators(value)
def create(self, validated_data):
instance, _ = models.MyModel.objects.get_or_create(**validated_data)
return instance
class Meta:
model = models.MyModel
The Serializer restore_object method was removed starting with the 3.0 version of REST Framework.
A straightforward way to add get_or_create functionality is as follows:
class MyObjectSerializer(serializers.ModelSerializer):
class Meta:
model = MyObject
fields = (
'unique_field',
'other_field',
)
def get_or_create(self):
defaults = self.validated_data.copy()
identifier = defaults.pop('unique_field')
return MyObject.objects.get_or_create(unique_field=identifier, defaults=defaults)
def post(self, request, format=None):
serializer = MyObjectSerializer(data=request.data)
if serializer.is_valid():
instance, created = serializer.get_or_create()
if not created:
serializer.update(instance, serializer.validated_data)
return Response(serializer.data, status=status.HTTP_202_ACCEPTED)
return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
However, it doesn't seem to me that the resulting code is any more compact or easy to understand than if you query if the instance exists then update or save depending upon the result of the query.
#Groady's answer works, but you have now lost your ability to validate the uniqueness when creating new objects (UniqueValidator has been removed from your list of validators regardless the cicumstance). The whole idea of using a serializer is that you have a comprehensive way to create a new object that validates the integrity of the data you want to use to create the object. Removing validation isn't what you want. You DO want this validation to be present when creating new objects, you'd just like to be able to throw data at your serializer and get the right behavior under the hood (get_or_create), validation and all included.
I'd recommend overwriting your is_valid() method on the serializer instead. With the code below you first check to see if the object exists in your database, if not you proceed with full validation as usual. If it does exist you simply attach this object to your serializer and then proceed with validation as usual as if you'd instantiated the serializer with the associated object and data. Then when you hit serializer.save() you'll simply get back your already created object and you can have the same code pattern at a high level: instantiate your serializer with data, call .is_valid(), then call .save() and get returned your model instance (a la get_or_create). No need to overwrite .create() or .update().
The caveat here is that you will get an unnecessary UPDATE transaction on your database when you hit .save(), but the cost of one extra database call to have a clean developer API with full validation still in place seems worthwhile. It also allows you the extensibility of using custom models.Manager and custom models.QuerySet to uniquely identify your model from a few fields only (whatever the primary identifying fields may be) and then using the rest of the data in initial_data on the Serializer as an update to the object in question, thereby allowing you to grab unique objects from a subset of the data fields and treat the remaining fields as updates to the object (in which case the UPDATE call would not be extra).
Note that calls to super() are in Python3 syntax. If using Python 2 you'd want to use the old style: super(MyModelSerializer, self).is_valid(**kwargs)
from django.core.exceptions import ObjectDoesNotExist, MultipleObjectsReturned
class MyModelSerializer(serializers.ModelSerializer):
def is_valid(self, raise_exception=False):
if hasattr(self, 'initial_data'):
# If we are instantiating with data={something}
try:
# Try to get the object in question
obj = Security.objects.get(**self.initial_data)
except (ObjectDoesNotExist, MultipleObjectsReturned):
# Except not finding the object or the data being ambiguous
# for defining it. Then validate the data as usual
return super().is_valid(raise_exception)
else:
# If the object is found add it to the serializer. Then
# validate the data as usual
self.instance = obj
return super().is_valid(raise_exception)
else:
# If the Serializer was instantiated with just an object, and no
# data={something} proceed as usual
return super().is_valid(raise_exception)
class Meta:
model = models.MyModel
There are a couple of scenarios where a serializer might need to be able to get or create Objects based on data received by a view - where it's not logical for the view to do the lookup / create functionality - I ran into this this week.
Yes it is possible to have get_or_create functionality in a Serializer. There is a hint about this in the documentation here: http://www.django-rest-framework.org/api-guide/serializers#specifying-which-fields-should-be-write-only where:
restore_object method has been written to instantiate new users.
The instance attribute is fixed as None to ensure that this method is not used to update Users.
I think you can go further with this to put full get_or_create into the restore_object - in this instance loading Users from their email address which was posted to a view:
class UserFromEmailSerializer(serializers.ModelSerializer):
class Meta:
model = get_user_model()
fields = [
'email',
]
def restore_object(self, attrs, instance=None):
assert instance is None, 'Cannot update users with UserFromEmailSerializer'
(user_object, created) = get_user_model().objects.get_or_create(
email=attrs.get('email')
)
# You can extend here to work on `user_object` as required - update etc.
return user_object
Now you can use the serializer in a view's post method, for example:
def post(self, request, format=None):
# Serialize "new" member's email
serializer = UserFromEmailSerializer(data=request.DATA)
if not serializer.is_valid():
return Response(serializer.errors,
status=status.HTTP_400_BAD_REQUEST)
# Loaded or created user is now available in the serializer object:
person=serializer.object
# Save / update etc.
A better way of doing this is to use the PUT verb instead, then override the get_object() method in the ModelViewSet. I answered this here: https://stackoverflow.com/a/35024782/3025825.
A simple workaround is to use to_internal_value method:
class MyModelSerializer(serializers.ModelSerializer):
def to_internal_value(self, validated_data):
instance, _ = models.MyModel.objects.get_or_create(**validated_data)
return instance
class Meta:
model = models.MyModel
I know it's a hack, but in case if you need a quick solution
P.S. Of course, editing is not supported
class ExpoDeviceViewSet(viewsets.ModelViewSet):
permission_classes = [IsAuthenticated, ]
serializer_class = ExpoDeviceSerializer
def get_queryset(self):
user = self.request.user
return ExpoDevice.objects.filter(user=user)
def perform_create(self, serializer):
existing_token = self.request.user.expo_devices.filter(
token=serializer.validated_data['token']).first()
if existing_token:
return existing_token
return serializer.save(user=self.request.user)
In case anyone needs to create an object if it does not exist on GET request:
class MyModelViewSet(viewsets.ModelViewSet):
queryset = models.MyModel.objects.all()
serializer_class = serializers.MyModelSerializer
def retrieve(self, request, pk=None):
instance, _ = models.MyModel.objects.get_or_create(pk=pk)
serializer = self.serializer_class(instance)
return response.Response(serializer.data)
Another solution, as I found that UniqueValidator wasn't in the validators for the serializer, but rather in the field's validators.
def is_valid(self, raise_exception=False):
self.fields["my_field_to_fix"].validators = [
v
for v in self.fields["my_field_to_fix"].validators
if not isinstance(v, validators.UniqueValidator)
]
return super().is_valid(raise_exception)
I'm trying to set some fields before saving an object that a user wants to insert. For example, if a user wants to create a new instance, before saving it, I want to set the field owner equal to request.user and then call the create method from the parent. I've achieved this with the following code:
class ClassView(viewsets.ModelViewSet):
queryset = ModelClass.objects.all()
serializer_class = ModelClassSerializer
def create(self, request, pk = None):
if ModelClass.objects.filter(pk = request.user.id):
return Response({'detail' : "This user is already inserted" }, status = status.HTTP_401_UNAUTHORIZED)
return super(ClassView, self).create(request, pk = None)
def pre_save(self, obj):
obj.user_id = ModelClass.objects.get(pk = self.request.user.id)
It could be also that I want to set an attribute of the model according to some calculation with values coming from the POST request (those values are established as fields in the serializer).
Is the pre_save solution the correct way to go or am I missing something?
Thanks in advance.
I would say this is the correct way to go but if you simply want to set the object's user to the current request user, instead of:
obj.user_id = ModelClass.objects.get(pk = self.request.user.id)
...just use:
obj.user = self.request.user
The rest framework pre_save hook is there for your exact requirement but there exists other ones you may find useful. See http://www.django-rest-framework.org/api-guide/generic-views#genericapiview - under Save / deletion hooks.
However, if you require this data to be saved on the object instance outside of the rest framework (i.e. additionally within a normal Django view) you will most probably want to use the Django pre_save signal and hook your model up to it. That way the request user will be stored each time the object is saved, not just via the rest framework: https://docs.djangoproject.com/en/dev/ref/signals/