I'm using django-rest-framework and python-social-auth in my Django project.
Here is the serializer class of UserSocialAuth model in my project
class SocialAuthSerializer(serializers.HyperlinkedModelSerializer):
id = serializers.CharField()
class Meta:
model = UserSocialAuth
fields = ('id', 'provider')
Then I want to an additional field UserSocialAuth.extra_data['login'] to above Serializer, the traditional way should be
class UserSocialAuth(AbstractUserSocialAuth):
def login:
return self.extra_data['login']
class SocialAuthSerializer(serializers.HyperlinkedModelSerializer):
login = serializers.CharField(source='login')
...
fields = ('id', 'provider', 'login')
The problem is that UserSocialAuth is belong to python-social-auth, I have to change the code of python-social-auth app directly to add def login:, so how can I add the additional field to the existing model UserSocialAuth without touching the code of python-social-auth.
I just find that I can use SerializerMethodField here, no need to change the raw class UserSocialAuth, just add one more field to the serializer like this:
class SocialAuthSerializer(serializers.HyperlinkedModelSerializer):
login = serializers.SerializerMethodField()
def get_login(self, obj):
return obj.extra_data['login']
I am looking for a way to properly ovverride the default .create() method of a ModelSerializer serializer in Django Rest Framework for dealing with an extra parameter.
In my original Django model I have just overridden the default.save() method for managing an extra param. Now .save() can be called also in this way: .save(extra = 'foo').
I have to create a ModelSerializer mapping on that original Django model:
from OriginalModels.models import OriginalModel
from rest_framework import serializers
class OriginalModelSerializer(serializers.ModelSerializer):
# model fields
class Meta:
model = OriginalModel
But in this way I can't pass the extra param to the model .save() method.
How can I properly override the .create() method of my OriginalModelSerializer class to take (eventually) this extra param into account?
Hmm. this might not be the perfect answer given I don't know how you want to pass this "extra" in (ie. is it an extra field in a form normally, etc)
What you'd probably want to do is just represent foo as a field on the serializer. Then it will be present in validated_data in create, then you can make create do something like the following
def create(self, validated_data):
obj = OriginalModel.objects.create(**validated_data)
obj.save(foo=validated_data['foo'])
return obj
You'd probably want to look at the default implementation of create for some of the other things it does though (like remove many-to-many relationships, etc.).
You can now do this in the view set (threw in user as a bonus ;) ):
class OriginalModelViewSet(viewsets.ModelViewSet):
"""
API endpoint that allows OriginalModel classes to be viewed or edited.
"""
serializer_class = OriginalModelSerializer
queryset = OriginalModel.objects.all()
def perform_create(self, serializer):
user = None
if self.request and hasattr(self.request, "user"):
user = self.request.user
serializer.save(user=user, foo='foo')
That way the Serializer can stay generic, i.e.:
class OriginalModelSerializer(serializers.HyperlinkedModelSerializer):
class Meta:
model = OriginalModel
fields = '__all__'
With Django REST Framework, a standard ModelSerializer will allow ForeignKey model relationships to be assigned or changed by POSTing an ID as an Integer.
What's the simplest way to get this behavior out of a nested serializer?
Note, I am only talking about assigning existing database objects, not nested creation.
I have hacked away around this in the past with additional 'id' fields in the serializer and with custom create and update methods, but this is such a seemingly simple and frequent issue for me that I'm curious to know the best way.
class Child(models.Model):
name = CharField(max_length=20)
class Parent(models.Model):
name = CharField(max_length=20)
phone_number = models.ForeignKey(PhoneNumber)
child = models.ForeignKey(Child)
class ChildSerializer(ModelSerializer):
class Meta:
model = Child
class ParentSerializer(ModelSerializer):
# phone_number relation is automatic and will accept ID integers
children = ChildSerializer() # this one will not
class Meta:
model = Parent
Updated on July 05 2020
This post is getting more attention and it indicates more people have a similar situation. So I decided to add a generic way to handle this problem. This generic way is best suitable for you if you have more serializers that need to change to this format
Since DRF doesn't provide this functionality out of the box, we need to create a serializer field first.
from rest_framework import serializers
class RelatedFieldAlternative(serializers.PrimaryKeyRelatedField):
def __init__(self, **kwargs):
self.serializer = kwargs.pop('serializer', None)
if self.serializer is not None and not issubclass(self.serializer, serializers.Serializer):
raise TypeError('"serializer" is not a valid serializer class')
super().__init__(**kwargs)
def use_pk_only_optimization(self):
return False if self.serializer else True
def to_representation(self, instance):
if self.serializer:
return self.serializer(instance, context=self.context).data
return super().to_representation(instance)
I am not well impressed with this class name, RelatedFieldAlternative, you can use anything you want.
Then use this new serializer field in your parent serializer as,
class ParentSerializer(ModelSerializer):
child = RelatedFieldAlternative(queryset=Child.objects.all(), serializer=ChildSerializer)
class Meta:
model = Parent
fields = '__all__'
Original Post
Using two different fields would be ok (as #Kevin Brown and #joslarson mentioned), but I think it's not perfect (to me). Because getting data from one key (child) and sending data to another key (child_id) might be a little bit ambiguous for front-end developers. (no offense at all)
So, what I suggest here is, override the to_representation() method of ParentSerializer will do the job.
def to_representation(self, instance):
response = super().to_representation(instance)
response['child'] = ChildSerializer(instance.child).data
return response
Complete representation of Serializer
class ChildSerializer(ModelSerializer):
class Meta:
model = Child
fields = '__all__'
class ParentSerializer(ModelSerializer):
class Meta:
model = Parent
fields = '__all__'
def to_representation(self, instance):
response = super().to_representation(instance)
response['child'] = ChildSerializer(instance.child).data
return response
Advantage of this method?
By using this method, we don't need two separate fields for creation and reading. Here both creation and reading can be done by using child key.
Sample payload to create parent instance
{
"name": "TestPOSTMAN_name",
"phone_number": 1,
"child": 1
}
Screenshot
The best solution here is to use two different fields: one for reading and the other for writing. Without doing some heavy lifting, it is difficult to get what you are looking for in a single field.
The read-only field would be your nested serializer (ChildSerializer in this case) and it will allow you to get the same nested representation that you are expecting. Most people define this as just child, because they already have their front-end written by this point and changing it would cause problems.
The write-only field would be a PrimaryKeyRelatedField, which is what you would typically use for assigning objects based on their primary key. This does not have to be write-only, especially if you are trying to go for symmetry between what is received and what is sent, but it sounds like that might suit you best. This field should have a source set to the foreign key field (child in this example) so it assigns it properly on creation and updating.
This has been brought up on the discussion group a few times, and I think this is still the best solution. Thanks to Sven Maurer for pointing it out.
Here's an example of what Kevin's answer is talking about, if you want to take that approach and use 2 separate fields.
In your models.py...
class Child(models.Model):
name = CharField(max_length=20)
class Parent(models.Model):
name = CharField(max_length=20)
phone_number = models.ForeignKey(PhoneNumber)
child = models.ForeignKey(Child)
then serializers.py...
class ChildSerializer(ModelSerializer):
class Meta:
model = Child
class ParentSerializer(ModelSerializer):
# if child is required
child = ChildSerializer(read_only=True)
# if child is a required field and you want write to child properties through parent
# child = ChildSerializer(required=False)
# otherwise the following should work (untested)
# child = ChildSerializer()
child_id = serializers.PrimaryKeyRelatedField(
queryset=Child.objects.all(), source='child', write_only=True)
class Meta:
model = Parent
Setting source=child lets child_id act as child would by default had it not be overridden (our desired behavior). write_only=True makes child_id available to write to, but keeps it from showing up in the response since the id already shows up in the ChildSerializer.
There is a way to substitute a field on create/update operation:
class ChildSerializer(ModelSerializer):
class Meta:
model = Child
class ParentSerializer(ModelSerializer):
child = ChildSerializer()
# called on create/update operations
def to_internal_value(self, data):
self.fields['child'] = serializers.PrimaryKeyRelatedField(
queryset=Child.objects.all())
return super(ParentSerializer, self).to_internal_value(data)
class Meta:
model = Parent
A few people here have placed a way to keep one field but still be able to get the details when retrieving the object and create it with only the ID. I made a little more generic implementation if people are interested:
First off the tests:
from rest_framework.relations import PrimaryKeyRelatedField
from django.test import TestCase
from .serializers import ModelRepresentationPrimaryKeyRelatedField, ProductSerializer
from .factories import SomethingElseFactory
from .models import SomethingElse
class TestModelRepresentationPrimaryKeyRelatedField(TestCase):
def setUp(self):
self.serializer = ModelRepresentationPrimaryKeyRelatedField(
model_serializer_class=SomethingElseSerializer,
queryset=SomethingElse.objects.all(),
)
def test_inherits_from_primary_key_related_field(self):
assert issubclass(ModelRepresentationPrimaryKeyRelatedField, PrimaryKeyRelatedField)
def test_use_pk_only_optimization_returns_false(self):
self.assertFalse(self.serializer.use_pk_only_optimization())
def test_to_representation_returns_serialized_object(self):
obj = SomethingElseFactory()
ret = self.serializer.to_representation(obj)
self.assertEqual(ret, SomethingElseSerializer(instance=obj).data)
Then the class itself:
from rest_framework.relations import PrimaryKeyRelatedField
class ModelRepresentationPrimaryKeyRelatedField(PrimaryKeyRelatedField):
def __init__(self, **kwargs):
self.model_serializer_class = kwargs.pop('model_serializer_class')
super().__init__(**kwargs)
def use_pk_only_optimization(self):
return False
def to_representation(self, value):
return self.model_serializer_class(instance=value).data
The usage is like so, if you have a serializer somewhere:
class YourSerializer(ModelSerializer):
something_else = ModelRepresentationPrimaryKeyRelatedField(queryset=SomethingElse.objects.all(), model_serializer_class=SomethingElseSerializer)
This will allow you to create an object with a foreign key still only with the PK, but will return the full serialized nested model when retrieving the object you created (or whenever really).
There is a package for that! Check out PresentablePrimaryKeyRelatedField in Drf Extra Fields package.
https://github.com/Hipo/drf-extra-fields
I think the approach outlined by Kevin probably would be the best solution, but I couldn't ever get it to work. DRF kept throwing errors when I had both a nested serializer and a primary key field set. Removing one or the other would function, but obviously didn't give me the result I needed. The best I could come up with is creating two different serializers for reading and writing, Like so...
serializers.py:
class ChildSerializer(serializers.ModelSerializer):
class Meta:
model = Child
class ParentSerializer(serializers.ModelSerializer):
class Meta:
abstract = True
model = Parent
fields = ('id', 'child', 'foo', 'bar', 'etc')
class ParentReadSerializer(ParentSerializer):
child = ChildSerializer()
views.py
class ParentViewSet(viewsets.ModelViewSet):
serializer_class = ParentSerializer
queryset = Parent.objects.all()
def get_serializer_class(self):
if self.request.method == 'GET':
return ParentReadSerializer
else:
return self.serializer_class
Here's how I've solved this problem.
serializers.py
class ChildSerializer(ModelSerializer):
def to_internal_value(self, data):
if data.get('id'):
return get_object_or_404(Child.objects.all(), pk=data.get('id'))
return super(ChildSerializer, self).to_internal_value(data)
You'll just pass your nested child serializer just as you get it from the serializer ie child as a json/dictionary. in to_internal_value we instantiate the child object if it has a valid ID so that DRF can further work with the object.
I started by implementing something similar to JPG's solution before I found this answer, and noticed that it breaks the built-in Django Rest Framework's templates. Now, that isn't such a big deal (as their solution works wonderfully via requests/postman/AJAX/curl/etc.), but if someone's new (like me) and wants the built-in DRF form to help them along the way, here's my solution (after cleaning it up and integrating some of JPG's ideas):
class NestedKeyField(serializers.PrimaryKeyRelatedField):
def __init__(self, **kwargs):
self.serializer = kwargs.pop('serializer', None)
if self.serializer is not None and not issubclass(self.serializer, serializers.Serializer):
raise TypeError('You need to pass a instance of serialzers.Serializer or atleast something that inherits from it.')
super().__init__(**kwargs)
def use_pk_only_optimization(self):
return not self.serializer
def to_representation(self, value):
if self.serializer:
return dict(self.serializer(value, context=self.context).data)
else:
return super().to_representation(value)
def get_choices(self, cutoff=None):
queryset = self.get_queryset()
if queryset is None:
return {}
if cutoff is not None:
queryset = queryset[:cutoff]
return OrderedDict([
(
self.to_representation(item)['id'] if self.serializer else self.to_representation(item), # If you end up using another column-name for your primary key, you'll have to change this extraction-key here so it maps the select-element properly.
self.display_value(item)
)
for item in queryset
])
and an example below,
Child Serializer class:
class ChildSerializer(serializers.ModelSerializer):
class Meta:
model = ChildModel
fields = '__all__'
Parent Serializer Class:
class ParentSerializer(serializers.ModelSerializer):
same_field_name_as_model_foreign_key = NestedKeyField(queryset=ChildModel.objects.all(), serializer=ChildSerializer)
class Meta:
model = ParentModel
fields = '__all__'
Based on the answers of both JPG and Bono, I came up with a solution that handles the OpenAPI Schema generator of DRF as well.
The actual field class is:
from rest_framework import serializers
class ModelRepresentationPrimaryKeyRelatedField(serializers.PrimaryKeyRelatedField):
def __init__(self, **kwargs):
self.response_serializer_class = kwargs.pop('response_serializer_class', None)
if self.response_serializer_class is not None \
and not issubclass(self.response_serializer_class, serializers.Serializer):
raise TypeError('"serializer" is not a valid serializer class')
super(ModelRepresentationPrimaryKeyRelatedField, self).__init__(**kwargs)
def use_pk_only_optimization(self):
return False if self.response_serializer_class else True
def to_representation(self, instance):
if self.response_serializer_class is not None:
return self.response_serializer_class(instance, context=self.context).data
return super(ModelRepresentationPrimaryKeyRelatedField, self).to_representation(instance)
The extended AutoSchema class is:
import inspect
from rest_framework.schemas.openapi import AutoSchema
from .fields import ModelRepresentationPrimaryKeyRelatedField
class CustomSchema(AutoSchema):
def _map_field(self, field):
if isinstance(field, ModelRepresentationPrimaryKeyRelatedField) \
and hasattr(field, 'response_serializer_class'):
frame = inspect.currentframe().f_back
while frame is not None:
method_name = frame.f_code.co_name
if method_name == '_get_request_body':
break
elif method_name == '_get_responses':
field = field.response_serializer_class()
return super(CustomSchema, self)._map_field(field)
frame = frame.f_back
return super(CustomSchema, self)._map_field(field)
Then on your Dganjo's project settings you can define this new Schema class to be used globally like:
REST_FRAMEWORK = {
'DEFAULT_SCHEMA_CLASS': '<path_to_custom_schema>.CustomSchema',
}
Lastly from within your models you can use the new field type like:
class ExampleSerializer(serializers.ModelSerializer):
test_field = ModelRepresentationPrimaryKeyRelatedField(queryset=Test.objects.all(), response_serializer_class=TestListSerializer)
I have been also stuck in the same situation. But what i have done that i have created two serializers for the following models as follow:
class Base_Location(models.Model):
Base_Location_id = models.AutoField(primary_key = True)
Base_Location_Name = models.CharField(max_length=50, db_column="Base_Location_Name")
class Location(models.Model):
Location_id = models.AutoField(primary_key = True)
Location_Name = models.CharField(max_length=50, db_column="Location_Name")
Base_Location_id = models.ForeignKey(Base_Location, db_column="Base_Location_id", related_name="Location_Base_Location", on_delete=models.CASCADE)
This is my parent serializer
class BaseLocationSerializer(serializers.ModelSerializer):
class Meta:
model = Base_Location
fields = "__all__"
I'm using this serializer only for get request so in response i got data with foreign key also because of nested serializer
class LocationSerializerList(serializers.ModelSerializer): <-- using for get request
Base_Location_id = BaseLocationSerializer()
class Meta:
model = Location
fields = "__all__"
Screenshot of get method request and response in postman
I'm using this serializer only for post request so while sending post request i do not need to include any additional information rather than primary key field value
class LocationSerializerInsert(serializers.ModelSerializer): <-- using for post request
class Meta:
model = Location
fields = "__all__"
Screenshot of post method request and response in postman
Here's what I'm using all over. This may be the simplest, most straight forward method which needs no hacks etc, and is directly using DRF without jumping thru hoops. Happy to hear disagreements with this approach.
In the view's perform_create (or equivalent), fetch the FK model database object corresponding to the field sent in the POST request, and then send that into the Serializer. The field in the POST request can be anything that can be used to filter and locate the DB object, need not be an ID.
This is documented here: https://www.django-rest-framework.org/api-guide/generic-views/#genericapiview
These hooks are particularly useful for setting attributes that are
implicit in the request, but are not part of the request data. For
instance, you might set an attribute on the object based on the
request user, or based on a URL keyword argument.
def perform_create(self, serializer):
serializer.save(user=self.request.user)
This method also has the advantage of maintaining parity between the read and write side, by not sending a nested representation for child in the response to the GET or POST.
Given the example posted by the OP:
class Child(models.Model):
name = CharField(max_length=20)
class Parent(models.Model):
name = CharField(max_length=20)
phone_number = models.ForeignKey(PhoneNumber)
child = models.ForeignKey(Child)
class ChildSerializer(ModelSerializer):
class Meta:
model = Child
class ParentSerializer(ModelSerializer):
# Note this is different from the OP's example. This will send the
# child name in the response
child = serializers.ReadOnlyField(source='child.name')
class Meta:
model = Parent
fields = ('name', 'phone_number', 'child')
In the View's perform_create:
class SomethingView(generics.ListCreateAPIView):
serializer_class = ParentSerializer
def perform_create(self, serializer):
child_name = self.request.data.get('child_name', None)
child_obj = get_object_or_404(Child.objects, name=child_name)
serializer.save(child=child_obj)
PS: Please note that I've not tested this above snippet, however its based on a pattern I'm using in many places so it should work as is.
Most of the tutorials on Django Rest Framework explains using the Django models and doing CRUD operations. That is a GET request on user model returns the attributes of user object in JSON format if I use JSON serializer.
I am designing my Django application to process a query and return response.
For example, I provide a REST API to get the results of the following query
"Get me the user first name and department whose salary than XXX"
Here are my Django models:
class UserProfile(AbstractUser):
age = models.PositiveIntegerField(_("age"))
salary=models.PositiveIntegerField(_("salary"))
AUTH_USER_MODEL = "profiles.UserProfile"
User = get_user_model()
class Department(models.Model):
users=models.ForeignKey(User)
dept_name = models.CharField(max_length=30)
Now I have the following DTO (Data transfer object):
class CustomResponse(object):
def __init__(self, user_name, salary, dept_name):
self.user_name = user_name
self.salary = salary
self.dept_name=dept_name
In my REST service implemented using DRF, I want the following
#api_view(['GET'])
def getNameandDept(salary):
users=User.objects.filter(salary__gt=salary)
toreturn=[]
for user in users:
response=CustomResponse(user.first_name,user.salary,user.dept_name)
to_return.append(response)
return Response(to_return)
I am not sure what is the right way to implement the above, with the tools that Django rest framework provide.
I am expecting the response something like this
[{user_name:"matt", salary:"5000", dept_name:"ENG"},{user_name:"smith",salary:"4000", dept_name:"HR"}....]
Thanks
EDIT
I was hoping DRF provides out of box tool for this kind of serialization. I have been using JAX-RS API (jersey and RESTeasy) that does this serialization.
You don't really need the REST Framework for this. All you need is to define a serializer class instead of the CustomResponse that you have.
in serializers.py
from django.core.serializers.json import Serializer
class UserSerializer(Serializer):
def get_dump_object(self, obj):
mapped_object = {
'user_name': obj.first_name,
'salary': obj.salary,
'dept_name': obj.dept_name
}
return mapped_object
then in your views.py
from myapp.serializers import UserSerializer
def getNameandDept(request, salary):
users = User.objects.filter(salary__gt=salary)
serializer = UserSerializer()
return HttpResponse(serializer.serialize(users), mimetype='application/json')
Don't forget to define the salary argument in your urls.py
url(r'^users/(?P<salary>\d+)$', views.getNameandDept, name='getNameandDept'),
PS. You absolutely can do this with the DRF as well. It is a basic GET call (the filtering by salary has no effect on the serializer), so all you need to do there is define a ModelSerializer subclass with just the three fields
class UserSerializer(serializers.ModelSerializer):
class Meta:
model = User
fields = ('first_name', 'salary', 'dept_name')
and then serialize the output (note the slightly different syntax)
serializer = UserSerializer(users)
return Response(serializer.data)
I have a model with a foreign key to group (the other fields don't matter):
class Project(models.Model) :
group = models.ForeignKey(Group)
...
I have a model form for this model:
class AddProjectForm(forms.ModelForm):
class Meta:
model = Project
fields = ["group","another"]
In my urls, I am using this in a generic view:
(r'^$', create_object, {'form_class':AddProjectForm, 'template_name':"form.html", 'login_required':True, 'extra_context':{'title':'Add a Project'}}),
That all works, but I want to have the group field display only the groups that the current user belongs to, not all of the groups available. I'd normally do this by passing in the user to the model form and overriding init if I wasn't in a generic view. Is there any way to do this with the generic view or do I need to go with a regular view to pass in that value?
This is gonna look dirty, since the generic view instantiates the form_class with no parameters. If you really want to use the generic_view you're gonna have to generate the class dynamically :S
def FormForUser(user):
class TmpClass(forms.ModelForm):
def __init__(self, *args, **kwargs):
super(TmpClass, self).__init__(*args, **kwargs)
self.fields['group'].queryset = user.group_set.all()
class Meta:
model = Project
fields = ['group', 'another']
Then wrap the create object view
#login_required # Only logged users right?
def create_project(request):
user = request.user
form_class = FormForUser(user)
return create_object(request, form_class=form_class, ..... )
My recommendation is to write your own view, it will give you more control on the long term and it's a trivial view.
No, you'll need to make a regular view. As can be seen by looking at the source code for create_object(), there's no functionality to pass in extra parameters to the modelform (in django 1.2):
http://code.djangoproject.com/svn/django/branches/releases/1.2.X/django/views/generic/create_update.py