Develop Reference

Django writable nested serializers, create method not working

I have a nested serializer, the create method does not work. I have searched over the internet and no method worked for me. The most popular one is the one listed below.
models.py
class Displays(models.Model):
id = models.CharField(primary_key=True, max_length=32,
default=generate_uuid)
name = models.CharField(max_length=45, blank=True, null=True)
class OrdersDj(models.Model):
id = models.CharField(primary_key=True, max_length=32,
default=generate_uuid)
class AdsDj(models.Model):
id = models.CharField(primary_key=True, max_length=32,
default=generate_uuid)
order = models.ForeignKey(
OrdersDj, on_delete=models.CASCADE, blank=False, null=True)
display = models.ForeignKey(
Displays, on_delete=models.CASCADE, blank=True, null=True)
serializers.py
class DisplaySerializer(serializers.ModelSerializer):
class Meta:
model = Displays
fields = "__all__"
class AdsSerializer(serializers.ModelSerializer):
display = DisplaySerializer()
def create(self, validated_data):
print("validated_data", validated_data)
display_id = validated_data.pop('display')
display = Displays.objects.get(id=display_id)
ad = Displays.objects.create(display=display, **validated_data)
return ad
class Meta:
model = Ads
fields = "__all__"
class OrderSerializer(serializers.ModelSerializer):
ads = AdsSerializer(source="adsdj_set", many=True)
def create(self, validated_data):
validated_data.pop('adsdj_set')
order = Orders.objects.create(**validated_data)
return order
class Meta:
model = Orders
fields = "__all__"
views.py
class AdsCreate(APIView):
def put(self, request):
print('request.data', request.data)
serializer = serializers.AdsSerializer(data=request.data)
if serializer.is_valid():
serializer.save()
print('serializer.data > serializer.valid', serializer.data)
return Response(serializer.data, status=status.HTTP_201_CREATED)
print('serializer.errors > serializer.invalid', serializer.errors)
return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
print outs
request.data <QueryDict: {'order': ['18bb2225cf6e407a943f2941072d06de'], 'display': ['91'], 'firstday': ['2021-12-4'], 'lastday': ['2021-12-21'], 'duration': ['17'], 'filetype': ['image/png'], 'originalname': ['Picture1.png'], 'price': ['2550'], 'status': ['0'], 'filehash': ['not available yet'], 'orderByNum': ['-1'], 'imgWidth': ['1061'], 'imgHeight': ['708'], 'image': [<InMemoryUploadedFile: Picture1.png (image/png)>]}>
serializer.errors > serializer.invalid {'display': [ErrorDetail(string='This field is required.', code='required')]}
I am giving the display field to the serializer that is the id of the display. In the create method I find that display and reference it in the new ad object. The display field is present in the request.data and passed to the serializer, the serializer complains that the display field is not present.
One version of sending json data
{"order":"18bb2225cf6e407a943f2941072d06de","display":{"id":91},"firstday":"2021-12-5","lastday":"2021-12-15","duration":11,"image":{},"filetype":"image/png","originalname":"Picture1.png","price":1650,"status":0,"filehash":"not available yet","orderByNum":-1,"imgWidth":1061,"imgHeight":708}

Try using different serializers for creation and representation.
class AdsCreateSerializer(serializers.ModelSerializer):
class Meta:
model = Ads
fields = "__all__"
class AdsSerializer(serializers.ModelSerializer):
display = DisplaySerializer()
class Meta:
model = Ads
fields = "__all__"

For display field, AdsSerializer expects the following structure;
"display": {"id": 91}
whereas you send this;
"display": 91

Django - Serializer not setting ManyToManyField

For some reason the following code isn't setting the hash_tags attribute under Post. The way I checked was I put a breakpoint at the return Response line in view.py and I checked the newly created Post object and the hash_tags attribute just returned an empty list. Also when I read the serializer.data, hash_tags is an empty list as well. Even though the HashTag table clearly created the hash tag found in the body. What's going on?
model.py
class Post(AbstractBaseModel):
creator = models.ForeignKey(
User, on_delete=models.CASCADE, related_name="post_creator")
join_goal = models.ForeignKey(JoinGoal, on_delete=models.CASCADE)
body = models.CharField(max_length=511, validators=[MinLengthValidator(5)])
hash_tags = models.ManyToManyField(HashTag)
type = models.CharField(
choices=PostType.choices,
max_length=50,
)
class HashTag(models.Model):
hash_tag = models.CharField(max_length=140, primary_key=True, validators=[
MinLengthValidator(1)])
Serializer.py
class HashTagSerializer(serializers.ModelSerializer):
class Meta:
model = HashTag
fields = ['hash_tag']
class PostSerializer(serializers.ModelSerializer):
hash_tags = HashTagSerializer(many=True, read_only=True)
class Meta:
model = Post
fields = ('creator', 'join_goal', 'body', 'uuid', 'created', 'type', 'updated_at', 'hash_tags')
view.py
#api_view(['POST'])
def post_create_update_post(request):
user_uuid = str(request.user.uuid)
request.data['creator'] = user_uuid
request.data['type'] = PostType.UPDATE
post_text = request.data['body']
hash_tags_list = extract_hashtags(post_text)
hash_tags = [HashTag.objects.get_or_create(hash_tag=ht)[0].hash_tag for ht in hash_tags_list]
request.data['hash_tags'] = hash_tags
try:
with transaction.atomic():
serializer = PostSerializer(data=request.data)
if serializer.is_valid(raise_exception=True):
post_obj = serializer.save()
except Exception as e:
return Response(dict(error=str(e),
user_message=error_message_generic),
status=status.HTTP_400_BAD_REQUEST)
return Response(serializer.data, status=status.HTTP_201_CREATED)
I also tried not setting read_only=True and get this error
this leads to ValidationError({'hash_tags': [ErrorDetail(string='This field is required.', code='required')]}) with request.data['hash_tags']=['Test']

You set read_only=True This is why hash_tags value not saving on the database.
hash_tags = HashTagSerializer(many=True, read_only=True)
Declare it without read_only like this:
hash_tags = HashTagSerializer(many=True)

I believe that you have to override the create and update method for the nested serializer in serializer.py:
class HashTagSerializer(serializers.ModelSerializer):
class Meta:
model = HashTag
fields = ['hash_tag']
class PostSerializer(serializers.ModelSerializer):
hash_tags = HashTagSerializer(many=True, read_only=True)
class Meta:
model = Post
fields = ('creator', 'join_goal', 'body', 'uuid', 'created', 'type', 'updated_at', 'hash_tags')
def create(self, validated_data):
hash_tags_data = validated_data.pop('hash_tags')
post = Post.objects.create(**validated_data)
for data in hash_tags_data:
hash_tag = HashTag.objects.get_or_create(**data)
post.hash_tags.add(hash_tag)
post.save()
return post

Return extra Fields along with model fields in JSON - Django

I am using a Modelserializer to serialize data. In one of the cases, I have to send some extra fields other than model fields to the UI. How can I do that? Below is my code -
My Model -
class Group(models.Model):
groupID = models.AutoField(primary_key=True, db_index=True)
groupName = models.CharField(verbose_name="Name", max_length=30)
sectionID = models.ForeignKey(Section, on_delete=models.PROTECT, db_column='sectionID')
My Serializer -
class GroupSerializer(serializers.ModelSerializer):
class Meta:
model = Group
fields = ['groupID', 'groupName', 'sectionID']
My View -
#api_view(['GET'])
#permission_classes((permissions.IsAuthenticated,))
def getGroupInfo(request):
groups = models.Group.objects.all()
for group in groups:
group.logical_fied = True if <Custom condition>
serializer = GroupSerializer(groups, many = True)
return Response(serializer.data)
Expected response on UI
[{
"groupID":1,
"groupName":"A",
"sectionID":1,
"logical_field":True
}]
Response I am getting
[{
"groupID":1,
"groupName":"A",
"sectionID":1
}]
In my serializer.data, I don't get logical_field on the UI as it is not defined in GroupSerializer. Is there any way to achieve this?

from rest_framework.serializers import (ModelSerializer, BooleanField)
class GroupSerializer(ModelSerializer):
logical_field = BooleanField(default=True)
class Meta:
model = Group
fields = ['groupID', 'groupName', 'sectionID', 'logical_field']

Django REST: Serializer lookup by UUID

I'm creating this simple shopping API in Django REST.
Internally I'm using IDs for foreign key constraints, while guuids are brought to the outside world.
For the checkout procedure, the user provides a list of article IDs he is willing to purchase. The object in the POST data thus looks as follows:
{
assets: [
{
'product': 'd9d5044d-2284-4d15-aa76-2eee3675035b',
'amount': 4
},
....
]
}
I'm using the following ticket/asset models:
# Ticket
class Ticket(models.Model):
uuid = models.UUIDField(default=uuid.uuid4, editable=False, unique=True)
owner = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='tickets', on_delete=models.CASCADE)
# Assets
class Asset(models.Model):
ticket = models.ForeignKey(Ticket, related_name='assets', on_delete=models.CASCADE)
stock_item = models.ForeignKey(Stock, related_name='stock_item', on_delete=models.SET_NULL, null=True)
amount = models.IntegerField(validators=[MinValueValidator(0)])
And the serializers look as follows:
# Asset serializer
class AssetSerializer(serializers.ModelSerializer):
class Meta:
model = Asset
fields = ('stock_item', 'amount')
# Ticket serializer
class TicketSerializer(WritableNestedModelSerializer):
owner = serializers.ReadOnlyField(source='owner.username')
assets = AssetSerializer(many=True)
class Meta:
model = Ticket
fields = ('uuid', 'owner', 'assets', )
def perform_create(self, serializer):
serializer.save(owner=self.request.user)
When posting an object of the type specified above, the following error is presented:
{"assets":[{"stock_item": ["Invalid type. Expected PK, received string"]}]}
Which I can't seem to solve, how do I instruct the serializer to use the uuid as the lookup value? I solved a similar problem on view-level earlier by using the lookup_field member, but that doesn't seem to solve it. Any suggestions?
Enter code here

If I have understood you correctly, a SlugRelatedField should be able to find the correct related object.
class AssetSerializer(serializers.ModelSerializer):
ticket = serializers.SlugRelatedField(
read_only=True,
slug_field='uuid',
queryset=Ticket.objects.all() # Might be redundant with read_only=True
)
class Meta:
model = Asset
fields = ('ticket', 'stock_item', 'amount')

Elaborating on #BjornW's comment:
class UUIDRelatedField(serializers.SlugRelatedField):
slug_field = 'uuid'
def __init__(self, **kwargs):
super().__init__(slug_field=self.slug_field, **kwargs)
def to_representation(self, obj):
return getattr(obj, self.slug_field).hex

unique_together of two field messes with read_only_fields

I have this code for rating lessons, user and lesson should be added automatically from request authorization and URL:
#views.py
class RatingViewSet(
mixins.ListModelMixin,
mixins.CreateModelMixin,
viewsets.GenericViewSet
):
permission_classes = [permissions.IsAuthenticated]
serializer_class = RatingSerializer
def perform_create(self, serializer):
lessonInstance = Lesson.objects.get(id = self.kwargs['lessonID'])
serializer.save(user=self.request.user, lesson = lessonInstance)
def get_queryset(self):
lessonID = self.kwargs['lessonID']
return Rating.objects.filter(user=self.request.user, lesson=lessonID)
#serializers.py
class RatingSerializer(serializers.ModelSerializer):
class Meta:
model = Rating
fields = ('id', 'lesson','user', 'difficulty')
read_only_fields = ('id', 'user','lesson')
#models.py
class Rating(models.Model):
user = models.ForeignKey(settings.AUTH_USER_MODEL)
lesson = models.ForeignKey('lessons.Lesson')
difficulty = models.IntegerField()
class meta:
unique_together('user','lesson')
I want to have max 1 rating per user/lesson, hence unique_together('user','lesson'). But there is a problem: as long as that constraint is in the code, requests without user or lesson fields get denied with field required error, even though they are read_only.
(If I migrate with unique_together('user','lesson'), then delete that line it works, but as soon as it's there I get errors.)
I want to keep that bit of code there so I don't accidentally remove the unique_together constraint on later migrations.

This is a special-case that requires a different approach. Here's what django-rest-framework documentation (see the Note) says about this case:
The right way to deal with this is to specify the field explicitly on
the serializer, providing both the read_only=True and default=…
keyword arguments.
In your case, you need to explicitly define the user and lesson fields on your RatingSerializer, like this:
class RatingSerializer(serializers.ModelSerializer):
user = serializers.PrimaryKeyRelatedField(read_only=True, default=serializers.CurrentUserDefault()) # gets the user from request
lesson = serializers.PrimaryKeyRelatedField(read_only=True, default=None) # or any other appropriate value
class Meta:
model = Rating
fields = ('id', 'lesson','user', 'difficulty')
Good luck!

If a field is read_only=True then the validated_data will ignore data of it => Cause error required field, read more at doc
I also met this issue in a similar context, then tried #iulian's answer above but with no luck!
This combo read_only + default behavior is not supported anymore, check this
I resolved this issue by 2 solutions:
My model:
class Friendship(TimeStampedModel):
"""Model present Friendship request"""
from_user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='friendship_from_user')
to_user = models.ForeignKey(User, on_delete=models.CASCADE, related_name='friendship_to_user')
class Meta:
unique_together = ('from_user', 'to_user')
Solution 1. Write your own CurrentUserDefault class to get the user id then set to default attribute data of serializer(Ref from #51940976)
class CurrentUserDefault(object):
def set_context(self, serializer_field):
self.user_id = serializer_field.context['request'].user.id
def __call__(self):
return self.user_id
class FriendshipSerializer(serializers.ModelSerializer):
from_user_id = serializers.HiddenField(default=CurrentUserDefault())
class Meta:
model = Friendship
fields = ('id', 'from_user', 'from_user_id', 'to_user', 'status')
extra_kwargs = {
'from_user': {'read_only': True},
}
Solution 2. Override the create method of serializer to set data for user id(Ref from this)
class FriendshipSerializer(serializers.ModelSerializer):
class Meta:
model = Friendship
fields = ('id', 'from_user', 'to_user', 'status')
extra_kwargs = {
'from_user': {'read_only': True},
}
def create(self, validated_data):
"""Override create to provide a user via request.user by default.
This is require since the read_only `user` filed is not included by default anymore since
https://github.com/encode/django-rest-framework/pull/5886.
"""
if 'user' not in validated_data:
validated_data['from_user'] = self.context['request'].user
return super(FriendshipSerializer, self).create(validated_data)
I hope this helps!