I have a question about dealing with m2m / through models and their presentation in django rest framework. Let's take a classic example:
models.py:
from django.db import models
class Member(models.Model):
name = models.CharField(max_length = 20)
groups = models.ManyToManyField('Group', through = 'Membership')
class Group(models.Model):
name = models.CharField(max_length = 20)
class Membership(models.Model):
member = models.ForeignKey('Member')
group = models.ForeignKey('Group')
join_date = models.DateTimeField()
serializers.py:
imports...
class MemberSerializer(ModelSerializer):
class Meta:
model = Member
class GroupSerializer(ModelSerializer):
class Meta:
model = Group
views.py:
imports...
class MemberViewSet(ModelViewSet):
queryset = Member.objects.all()
serializer_class = MemberSerializer
class GroupViewSet(ModelViewSet):
queryset = Group.objects.all()
serializer_class = GroupSerializer
When GETing an instance of Member, I successfully receive all of the member's fields and also its groups - however I only get the groups' details, without extra details that comes from the Membership model.
In other words I expect to receive:
{
'id' : 2,
'name' : 'some member',
'groups' : [
{
'id' : 55,
'name' : 'group 1'
'join_date' : 34151564
},
{
'id' : 56,
'name' : 'group 2'
'join_date' : 11200299
}
]
}
Note the join_date.
I have tried oh so many solutions, including of course Django Rest-Framework official page about it and no one seems to give a proper plain answer about it - what do I need to do to include these extra fields? I found it more straight-forward with django-tastypie but had some other problems and prefer rest-framework.
How about.....
On your MemberSerializer, define a field on it like:
groups = MembershipSerializer(source='membership_set', many=True)
and then on your membership serializer you can create this:
class MembershipSerializer(serializers.HyperlinkedModelSerializer):
id = serializers.Field(source='group.id')
name = serializers.Field(source='group.name')
class Meta:
model = Membership
fields = ('id', 'name', 'join_date', )
That has the overall effect of creating a serialized value, groups, that has as its source the membership you want, and then it uses a custom serializer to pull out the bits you want to display.
EDIT: as commented by #bryanph, serializers.field was renamed to serializers.ReadOnlyField in DRF 3.0, so this should read:
class MembershipSerializer(serializers.HyperlinkedModelSerializer):
id = serializers.ReadOnlyField(source='group.id')
name = serializers.ReadOnlyField(source='group.name')
class Meta:
model = Membership
fields = ('id', 'name', 'join_date', )
for any modern implementations
I was facing this problem and my solution (using DRF 3.6) was to use SerializerMethodField on the object and explicitly query the Membership table like so:
class MembershipSerializer(serializers.ModelSerializer):
"""Used as a nested serializer by MemberSerializer"""
class Meta:
model = Membership
fields = ('id','group','join_date')
class MemberSerializer(serializers.ModelSerializer):
groups = serializers.SerializerMethodField()
class Meta:
model = Member
fields = ('id','name','groups')
def get_groups(self, obj):
"obj is a Member instance. Returns list of dicts"""
qset = Membership.objects.filter(member=obj)
return [MembershipSerializer(m).data for m in qset]
This will return a list of dicts for the groups key where each dict is serialized from the MembershipSerializer. To make it writable, you can define your own create/update method inside the MemberSerializer where you iterate over the input data and explicitly create or update Membership model instances.
I just had the same problem and I ended it up solving it with an annotation on the group queryset.
from django.db.models import F
class MemberSerializer(ModelSerializer):
groups = serializers.SerializerMethodField()
class Meta:
model = Member
def get_groups(self, instance):
groups = instance.groups.all().annotate(join_date=F(membership__join_date))
return GroupSerializer(groups, many=True).data
class GroupSerializer(ModelSerializer):
join_date = serializers.CharField(required=False) # so the serializer still works without annotation
class Meta:
model = Group
fields = ..., 'join_date']
NOTE: As a Software Engineer, I love to use Architectures and I have deeply worked on Layered Approach for Development so I am gonna be Answering it with Respect to Tiers.
As i understood the Issue, Here's the Solution
models.py
class Member(models.Model):
member_id = models.AutoField(primary_key=True)
member_name = models.CharField(max_length =
class Group(models.Model):
group_id = models.AutoField(primary_key=True)
group_name = models.CharField(max_length = 20)
fk_member_id = models.ForeignKey('Member', models.DO_NOTHING,
db_column='fk_member_id', blank=True, null=True)
class Membership(models.Model):
membershipid = models.AutoField(primary_key=True)
fk_group_id = models.ForeignKey('Group', models.DO_NOTHING,
db_column='fk_member_id', blank=True, null=True)
join_date = models.DateTimeField()
serializers.py
import serializer
class AllSerializer(serializer.Serializer):
group_id = serializer.IntegerField()
group_name = serializer.CharField(max_length = 20)
join_date = serializer.DateTimeField()
CustomModels.py
imports...
class AllDataModel():
group_id = ""
group_name = ""
join_date = ""
BusinessLogic.py
imports ....
class getdata(memberid):
alldataDict = {}
dto = []
Member = models.Members.objects.get(member_id=memberid) #or use filter for Name
alldataDict["MemberId"] = Member.member_id
alldataDict["MemberName"] = Member.member_name
Groups = models.Group.objects.filter(fk_member_id=Member)
for item in Groups:
Custommodel = CustomModels.AllDataModel()
Custommodel.group_id = item.group_id
Custommodel.group_name = item.group_name
Membership = models.Membership.objects.get(fk_group_id=item.group_id)
Custommodel.join_date = Membership.join_date
dto.append(Custommodel)
serializer = AllSerializer(dto,many=True)
alldataDict.update(serializer.data)
return alldataDict
You would technically, have to pass the Request to DataAccessLayer which would return the Filtered Objects from Data Access Layer but as I have to Answer the Question in a Fast Manner so i adjusted the Code in Business Logic Layer!
Related
I would like to do the following with Django REST Framework:
Filter results based on a field of a manytomany field.
The query would look like this:
https://endpoint.com/api/artwork/?having_style=Modern,Contemporary
I would expect the result to contain all ArtWork objects which contain a relation to a Style object with name "Modern", "Contemporary" or both.
The code below is not working and I don't know why.
models.py
class Style(models.Model):
name = models.CharField(validators=[validate_style], max_length=100, unique=True)
class ArtWork(models.Model):
styles = models.ManyToManyField(Style, default=None)
filters.py
class ArtWorkFilter(filters_rest.FilterSet):
having_style = django_filters.Filter(field_name="styles__name", lookup_expr='in')
class Meta:
model = ArtWork
fields = ['having_style']
class StyleSerializer(serializers.ModelSerializer):
class Meta:
model = Style
fields = ('name',)
class ArtWorkSerializer(serializers.ModelSerializer):
styles = StyleSerializer(many=True)
class Meta:
model = ArtWork
fields = ('styles'/)
views.py
class ArtWorkViewSet(viewsets.ModelViewSet):
permission_classes = []
queryset = ArtWork.objects.all()
serializer_class = ArtWorkSerializer
filter_backends = [filters_rest.DjangoFilterBackend,]
filterset_class= ArtWorkFilter
pagination_class = CursorSetPagination
Thank you in advance!
Solution
I solved it by changing the ArtWorkFilter to
filters.py
class ArtWorkFilter(filters_rest.FilterSet):
having_style = django_filters.Filter(field_name="styles__name", lookup_expr='in')
class Meta:
model = ArtWork
fields = ['having_style']
def filter_by_style_name(self, queryset, name, value):
list_styles = value.split(',')
return queryset.filter(styles__name__in=list_styles)
Try adding method param in Filter declaration. Something like:
class ArtWorkFilter(filters_rest.FilterSet):
having_style = django_filters.Filter(field_name="styles__name", lookup_expr='in')
class Meta:
model = ArtWork
fields = ['having_style']
def filter_by_style_name(self, queryset, name, value):
list_styles = value.split(',')
return queryset.filter(styles__name__in=list_styles)
CartItem.objects.filter(cart=cart, product=product, attribute__in=attribute_list).annotate(num_attr=Count('attribute')).filter(num_attr=len(attribute_list))
I have 3 models: Maker, Item and MakerItem that creates the relation between the items and their makers:
class Maker(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4)
name = models.CharField(max_length=100)
class Item(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4)
name = models.CharField(max_length=100)
class MakerItem(models.Model):
id = models.UUIDField(primary_key=True, default=uuid.uuid4)
item_id = models.ForeignKey(Item, on_delete=models.CASCADE)
maker_id = models.ForeignKey(Maker, on_delete=models.CASCADE)
the items can have a random amount of makers.
I want to create both the Item and the MakerItem objects at the same time with a single set of data,
for example if a Maker with id = "abcd" already exists, and I go to /item and send a POST request with the following data:
{
"name": "item1",
"makers": [
{
"maker_id": "abcd"
}
]
}
I want the serializer to create the Item object and the MakerItem object.
I have achieved this, with the following setup:
views.py
class ItemListCreate(ListCreateAPIView):
queryset = Item.objects.all()
serializer_class = ItemSerializer
serializers.py
class ItemSerializer(serializers.ModelSerializer):
class MakerItemSerializer(serializers.ModelSerializer):
class Meta:
model = MakerItem
exclude = ['id', 'item_id']
makers = MakerItemSerializer(many=True)
class Meta:
model = Item
fields = ['id', 'name', 'makers']
def create(self, validated_data):
maker_item_data = validated_data.pop('makers')
item_instance = Item.objects.create(**validated_data)
for each in maker_item_data:
MakerItem.objects.create(
item_id=check_instance,
maker_id=each['maker_id']
)
return item_instance
but when Django tries to return the created object, it always gives me the error:
AttributeError at /item/
Got AttributeError when attempting to get a value for field `makers` on serializer `ItemSerializer`.
The serializer field might be named incorrectly and not match any attribute or key on the `Item` instance.
Original exception text was: 'Item' object has no attribute 'makers'.
What am I doing wrong?
Thanks
EDIT: To clarify, the objects get created and populate the database correctly, but when the browsable API that DRF provides tries to display the created object, it gives me the error above.
Change:
class ItemSerializer(serializers.ModelSerializer):
class MakerItemSerializer(serializers.ModelSerializer):
class Meta:
model = MakerItem
exclude = ['id', 'item_id']
makers = MakerItemSerializer(many=True)
To:
class ItemSerializer(serializers.ModelSerializer):
class MakerItemSerializer(serializers.ModelSerializer):
class Meta:
model = MakerItem
exclude = ['id', 'item_id']
makers = MakerItemSerializer(many=True, source="makeritem_set")
Hope this works!
For clarity, you're attempting to serialise the reverse relationship between MakerItem and Item for this serialiser.
This means that the attribute on your object is automatically set by Django as fieldname_set but you can override this behaviour by setting the related_name kwarg on the field and then makemigrations and migrate it.
In your case you would need to do:
maker_id = models.ForeignKey(Maker, on_delete=models.CASCADE, related_name="maker_items")
And then update the field in the Meta to match the new field name, this way you don't have to manually specify source. Because actually the attribute "makers" is misleading, due to the fact its actually the MakerItem, not the Maker itself.
See https://docs.djangoproject.com/en/3.2/ref/models/relations/ for further details about this behaviour.
I am using Django Rest and my request parameter contains:
[
{
"job_role": 2,
"technology": 1
},
{
"job_role": 1,
"technology": 1
},
{
"job_role": 2,
"technology": 1
}
]
My models are:
class Technology(models.Model):
name = models.CharField(max_length=50)
def __str__(self):
return self.name
class JobRole(models.Model):
role_name = models.CharField(max_length=100)
def __str__(self):
return self.role_name
class ExpertPricing(models.Model):
role_name = models.OneToOneField(JobRole, related_name="role", on_delete=models.SET_NULL, null=True)
experience_in_years = models.PositiveBigIntegerField()
technology = models.OneToOneField(Technology, related_name="technology", on_delete=models.SET_NULL, null=True)
salary_per_month = models.PositiveBigIntegerField()
My view looks like this:
class PricingView(APIView):
def post(self, request):
datas = request.data
data_list = []
for data in datas:
job_role_id = data["job_role"]
technology_id = data["technology"]
job_role = JobRole.objects.get(pk=job_role_id)
technology = Technology.objects.get(pk=technology_id)
expert_pricing = ExpertPricing.objects.filter(role_name=job_role, technology=technology)
if expert_pricing:
data_list.append(expert_pricing)
serializer = ExpertPricingSerializer(data_list, many=True)
return Response(serializer.data, status=status.HTTP_200_OK)
serializers.py
class TechnologySerializer(serializers.ModelSerializer):
class Meta:
model = Technology
fields = ("id", "name")
class JobRoleSerializer(serializers.ModelSerializer):
class Meta:
model = JobRole
fields = ("id","role_name")
class ExpertPricingSerializer(serializers.ModelSerializer):
role = JobRoleSerializer(many=False, read_only=True)
technology = TechnologySerializer(many=False, read_only=True)
class Meta:
model = ExpertPricing
fields = "__all__"
I am unable to understand why data_list is not being serialized.
the error says:
AttributeError: Got AttributeError when attempting to get a value for field `experience_in_years` on serializer `ExpertPricingSerializer`.
The serializer field might be named incorrectly and not match any attribute or key on the `QuerySet` instance.
Original exception text was: 'QuerySet' object has no attribute 'experience_in_years'.
Since you defined in your model that those two fields (experience_in_years and salary_per_month) can not be empty, it seems like you need to do one of these things:
Send experience_in_years and salary_per_month fields in your request too.
Give a default value to those fields
Make it null=True, blank=True
If you do 2 or 3 those solutions require migration, keep that in mind, after doing one of those things you should be good to go
I've been bugging on this issue for some time now. I have two models : Acquisitions and RawDatas.
Each RawData have one Acquisition, but many RawDatas can have the same Acquisition.
I want to create or get the instance of Acquisition automatically when I create my RawDatas. And I want to be able to have all informations using the serializer.
class Acquisitions(models.Model):
class Meta:
unique_together = (('implant', 'beg_acq', 'duration_acq'),)
id = models.AutoField(primary_key=True)
implant = models.ForeignKey("Patients", on_delete=models.CASCADE)
beg_acq = models.DateTimeField("Beggining date of the acquisition")
duration_acq = models.DurationField("Duration of the acquisition")
class RawDatas(models.Model):
class Meta:
unique_together = (('acq', 'data_type'),)
id = models.AutoField(primary_key=True)
acq = models.ForeignKey("Acquisitions", on_delete=models.CASCADE)
data_type = models.CharField(max_length=3)
sampling_freq = models.PositiveIntegerField("Sampling frequency")
bin_file = models.FileField(db_index=True, upload_to='media')
And my serializers are these :
class AcquisitionSerializer(serializers.ModelSerializer):
class Meta:
model = Acquisitions
fields = ('id', 'implant', 'beg_acq', 'duration_acq')
class RawDatasSerializer(serializers.ModelSerializer):
acq = AcquisitionSerializer()
class Meta:
model = RawDatas
fields = ('id', 'data_type', 'sampling_freq', 'bin_file', 'acq')
def create(self, validated_data):
acq_data = validated_data.pop('acq')
acq = Acquisitions.objects.get_or_create(**acq_data)
RawDatas.objects.create(acq=acq[0], **validated_data)
return rawdatas
My problem is that, using this, if my instance of Acquisitions already exists, I get a non_field_errors or another constraint validation error.
I would like to know what is the correct way to handle this please ?
So I can automatically create this using the nested serializer, and when I only want to have informations (such as a GET request), I can have all the field I need (every field of the two models).
Thanks in advance for your help !
Try this:
class AcquisitionSerializer(serializers.ModelSerializer):
class Meta:
model = Acquisitions
fields = ('id', 'implant', 'beg_acq', 'duration_acq')
class RawDatasSerializer(serializers.ModelSerializer):
class Meta:
model = RawDatas
fields = ('id', 'data_type', 'sampling_freq', 'bin_file', 'acq')
def create(self, validated_data):
acq_data = validated_data.pop('acq')
acq = Acquisitions.objects.filter(id=acq_data.get('id')).first()
if not acq:
acq = AcquisitionSerializer.create(AcquisitionSerializer(), **acq_data)
rawdata = RawDatas.objects.create(acq=acq, **validated_data)
return rawdata
These are my models here:
class Site(models.Model):
siteID = models.CharField(max_length=255, primary_key=True)
class EndDevice(models.Model):
class Meta:
unique_together = ("edevID", "siteID")
edevID = models.CharField(max_length=255)
siteID = models.ForeignKey(Site, related_name='endDeviceList', on_delete=models.CASCADE)
deviceCategory = models.BigIntegerField()
This is my serilaizer:
class DeviceSerializer(serializers.ModelSerializer):
class Meta:
model = EndDevice
fields = ("edevID", "siteID", "deviceCategory")
class SiteSerializer(serializers.ModelSerializer):
endDeviceList = DeviceSerializer(many = True, read_only=True)
class Meta:
model = Site
fields = ("siteID", "endDeviceList")
This is my view:
class IndividualSite(generics.RetrieveUpdateDestroyAPIView):
'''
PUT site/{siteID}/
GET site/{siteID}/
DELETE site/{siteID}/
'''
queryset = EndDevice.objects.all()
serializer_class = SiteSerializer
I am trying to get/put/delete results using this class and I am trying to get all the EndDevice instances which have same siteID. But my serialzer only shows the siteID and doesn't show the endDeviceList (which should have the instants of the model EndDevice)
The problem is quite similar to this link:django rest-farmework nested relationships.
I have been trying different ways to serialize the objects, I think this is probably the smartest way, but have been really unsucccessful. Any help will be appreciated.
The urls.py:
urlpatterns = [
urlpatterns = [path('site/<str:pk>/', IndividualSite.as_view(), name = "get-site"),]
And it is connected to the main urls.
you are using read_only field for the Foreign relationship, remove that, as read_only wont display them
class SiteSerializer(serializers.ModelSerializer):
endDeviceList = DeviceSerializer(many = True)