We Keep Coding

Getting AttribueError by SlugRelatedField despite the object being saved

I am creating an API to save class teachers. Now all the fields in the ClassTeacher model are foreign fields so I am using a SlugRelatedField in the serializer. It looks like SlugRelatedField does not support attribute lookup like this "user__username" and raises attribute error HOWEVER the object is still being saved.
models.py
class ClassTeacher(models.Model):
teacher = models.ForeignKey(Teacher, on_delete=models.CASCADE)
class_name = models.ForeignKey(Classes, on_delete=models.CASCADE)
school_id = models.ForeignKey(School, on_delete=models.CASCADE)
serializers.py
class ClassTeacherSerializer(ModelSerializer):
teacher = SlugRelatedField(slug_field='user__username', queryset=Teacher.objects.all()) <---- this is causing the error
class_name = SlugRelatedField(slug_field='class_name', queryset=Classes.objects.all())
school_id = SlugRelatedField(slug_field='school_id__username', queryset=School.objects.all()) <---- and I am assuming that this will too
class Meta:
model = ClassTeacher
fields = '__all__'
I tried adding a #property in the Teacher model to retrieve the username and use the property in the slug_field but that did not work too.
How can I save the object without getting the error?
EDIT 1:
teachers/models.py
class Teacher(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
name = models.CharField(max_length=30)
photo = models.URLField()
teacher/serializers.py
class TeacherSerializer(ModelSerializer):
class Meta:
model = Teacher
fields = '__all__'
school/models.py
class School(models.Model):
school_id = models.OneToOneField(User, on_delete=models.CASCADE)
principal = models.CharField(max_length=50)
name = models.CharField(max_length=50)
photo = models.URLField()
school/serializers.py
class SchoolSerializer(ModelSerializer):
class Meta:
model = School
fields = '__all__'
EDIT 2:
Here's how I used the #property by referring from here:
teacher/models.py
class Teacher(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
name = models.CharField(max_length=30)
photo = models.URLField()
#Here's the extra property part
#property
def username(self):
return self.user.username
classteacher/serializers.py
class ClassTeacherSerializer(ModelSerializer):
#Here I changed user__username to just username as mentioned in the above link
teacher = SlugRelatedField(slug_field='username', queryset=Teacher.objects.all())
class_name = SlugRelatedField(slug_field='class_name', queryset=Classes.objects.all())
school_id = SlugRelatedField(slug_field='school_id__username', queryset=School.objects.all())
class Meta:
model = ClassTeacher
fields = '__all__'

try renaming serializer field from teacher to user and using slug_field='username'

You can use #property for example
class User(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE)
name = models.CharField(max_length=30)
photo = models.URLField()
#property
def get_username(self):
return Teacher.objects.filter(user_id=self.id)
and than inside your ClassTeacherSerializer use slug_field='username'
let me know if it works.

Django Rest Framework: 'RelatedManager' object has no attribute 'body' error when using nested serializer

With Django DRF, I am trying to display the comments for a particular post in a blog using a nested serializer.
I have run into the following error:
'RelatedManager' object has no attribute 'body'
Here is my code:
comment model:
class Comment(models.Model):
#adapted from https://blog.logrocket.com/use-django-rest-framework-to-build-a-blog/
created = models.DateTimeField(auto_now_add=True)
body = models.TextField(blank=False)
user_id = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='comments', on_delete=models.CASCADE)
post = models.ForeignKey('Posts', related_name='comments', on_delete=models.CASCADE)
#property
def time_left(self):
return self.post.time_left
Post model:
class Posts(models.Model):
title = models.CharField(max_length=100)
topic = MultiSelectField(choices=TOPIC_CHOICES)
creation_timestamp = models.DateTimeField(auto_now_add=True)
expiration_timestamp = models.DateTimeField(default=expiration)
body = models.CharField(max_length=255)
user_id = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE) #related_name='posts'
likes = models.ManyToManyField(settings.AUTH_USER_MODEL, related_name="likes",blank=True)
dislikes = models.ManyToManyField(settings.AUTH_USER_MODEL, related_name="dislikes",blank=True)
#property
def is_expired(self):
#taken from https://stackoverflow.com/questions/41505243/how-to-automatically-change-model-fields-in-django
if now() > self.expiration_timestamp:
return True
return False
#property
def time_left(self):
return self.expiration_timestamp - now()
serializers.py:
class CommentSerializer(serializers.ModelSerializer):
time_left = serializers.ReadOnlyField()
class Meta:
model = Comment
fields = ('created', 'body', 'user_id', 'post','time_left')
class PostsSerializer(serializers.ModelSerializer):
is_expired = serializers.ReadOnlyField()
time_left = serializers.ReadOnlyField()
comments = CommentSerializer(source='comments.body',) ########## THIS IS THE PROBLEMATIC LINE #######
class Meta:
#make sure that the relevant fields are read only
model = Posts
fields = ('comments','title','topic','creation_timestamp','expiration_timestamp','body','user_id','likes','dislikes','is_expired','time_left')
I believe the problematic line is the following one from serializers.py:
comments = CommentSerializer(source='comments.body',)

I think you are confusing the different keywords that a serializer can receive. Here I leave you an answer so that you understand it perfectly.
Your comments variable should look like this.
comments = CommentSerializer(many=True)

check if object in ManyToMany field django rest framework

here is my models.py:
class Post(models.Model):
id = models.AutoField(primary_key=True)
body = models.TextField(max_length=10000)
date = models.DateTimeField(auto_now_add=True, blank=True)
user = models.ForeignKey(User, on_delete=models.CASCADE)
liked_by = models.ManyToManyField(User, blank=True, related_name='liked_by')
class Meta:
ordering = ['-date']
serializers.py:
class PostSerializer(serializers.ModelSerializer):
user = UserSerializers()
total_likes = serializers.SerializerMethodField()
total_comments = serializers.SerializerMethodField()
class Meta:
model = Post
fields = ('id','body','date','user','total_likes','total_comments')
def get_total_likes(self, instance):
return instance.liked_by.count()
def get_total_comments(self, instance):
return instance.comment_set.count()
Q1: how do i check if a user exists in ManyToManyField of a single post?
Q2: shouldn't i use ManyToManyField in drf? then which would be better?

I don't have enough reps to comment, but if you have a post instance and a user instance, you could do something like:
post.liked_by.filter(id=user.id).exists()
Does that help you or are you asking where you should be implementing this? e.g. in your view or serializer etc...

Object of type 'ListSerializer' is not JSON serializable

I want to get all customer data and responses and also remarks.
This is model.py
class Customer(models.Model):
name = models.CharField(max_length=200)
email_address = models.CharField(max_length=200)
phone_number = models.CharField(max_length=20)
age = models.SmallIntegerField(default=14)
remarks = models.ManyToManyField(Remark,null=True,blank=True)
created_at = models.DateTimeField(auto_now_add=True)
def __str__(self):
return str(self.id)
class Response(models.Model):
question = models.ForeignKey(Question)
customer = models.ForeignKey(Customer)
response_text = models.CharField(max_length=100, null=True, blank=True)
created_at = models.DateTimeField(auto_now_add=True)
uuid = models.UUIDField()
def __str__(self):
return str(self.id)
This is serializers.py
class ResponseSerializer(ModelSerializer):
class Meta:
model = Response
fields = '__all__'
class RemarksSerializer(ModelSerializer):
class Meta:
model = Remark
fields = '__all__'
class CustomerInformationSerializer(ModelSerializer):
remarks = RemarksSerializer(many=True)
responses = serializers.SerializerMethodField()
def get_responses(self, obj):
responses = Response.objects.filter(customer=obj)
return ResponseSerializer(responses, many=True)
class Meta:
model = Customer
fields = ('name', 'email_address', 'phone_number', 'age', 'remarks', 'responses')
This is services.py
def customer_information(company_id=1):
cus = Customer.objects.filter(remarks__company_id=company_id)
return CustomerInformationSerializer(cus, many=True).data
This is views.py
class CustomerInformationView(APIView):
def get(self, request):
company_id = request.GET.get('company_id', 1)
resp = {'data': customer_information(company_id)}
return Response(data=resp, status=status.HTTP_200_OK)
This is url.py
url(r'^customer/$', CustomerInformationView.as_view()),
I'm having this problem. How can I solve this. Kindly guide me.

get function in your view should return responses.data, insted of responsed.

SIDE NOTE
First, let me point you to a resource that I think is GREAT for anything dealing with Django REST Framework:
Classy Django REST Framework. It is a fantastic resource because you can easily dig right into the source code to see how you may or may not need to override default operations.
MY ANSWER
What I suggest is that instead of using the APIView, you use ListAPIView.
It would look something like this:
from rest_framework.generics import ListAPIView
class Customer(models.Model):
name = models.CharField(max_length=200)
email_address = models.CharField(max_length=200)
phone_number = models.CharField(max_length=20)
age = models.SmallIntegerField(default=14)
remarks = models.ManyToManyField(Remark,null=True,blank=True)
created_at = models.DateTimeField(auto_now_add=True)
def __str__(self):
return str(self.id)
class Response(models.Model):
question = models.ForeignKey(Question)
customer = models.ForeignKey(Customer, related_name='responses')
response_text = models.CharField(max_length=100, null=True, blank=True)
created_at = models.DateTimeField(auto_now_add=True)
uuid = models.UUIDField()
def __str__(self):
return str(self.id)
class ResponseSerializer(ModelSerializer):
class Meta:
model = Response
fields = '__all__'
class RemarksSerializer(ModelSerializer):
class Meta:
model = Remark
fields = '__all__'
class CustomerInformationSerializer(ModelSerializer):
remarks = RemarksSerializer(many=True)
responses = ResponseSerializer(many=True)
class Meta:
model = Customer
fields = ('name', 'email_address', 'phone_number', 'age', 'remarks', 'responses')
class CustomerInformationView(ListAPIView):
queryset = Customer.objects.all()
serializer_class = CustomerInformationSerializer
lookup_field = 'remarks__company'
Note the change that I made by adding related_name to the customer field on your Response model. See Django documentation for more information on related_name. In short, it adds responses as a field name on your Customer model so that you can travel backwards through that relationship.
This is not tested, but this should be a better strategy to do what you want without having to have a get_responses method, or a services.py.

Some there might be error because of missing "/" at the end of path like "event-api"=incorrect and "event-api/" correct. That worked for me. Hope you also have same problem.
Incorrect: path('event-api',views.event_view,name="event-view")
Correct: path('event-api/',views.event_view,name="event-view")

How to display a foreign key value instead of the id?

I have the following models :
class FlightSchedule(models.Model):
tail_number = models.ForeignKey(TailNumber, null=False)
flight_number = models.CharField(max_length=30, null=False)
flight_group_code = models.ForeignKey(FlightGroup, null=False)
origin_port_code = models.ForeignKey(Port, null=False, related_name="Origin")
destination_port_code = models.ForeignKey(Port, null=False, related_name="Destination")
flight_departure_time = models.TimeField()
start_date = models.DateField()
end_date = models.DateField()
def __unicode__(self):
return u'%s' % self.flight_number
class Meta:
verbose_name_plural = "Flight Schedule"
class FlightScheduleDetail(models.Model):
flight_date = models.CharField(max_length=30, null=False)
flight_number = models.ForeignKey(FlightSchedule, null=False, related_name="flight_number_schedule")
route_id = models.CharField(max_length=30, null=False, unique=True)
flight_status = models.ForeignKey(Status, null=True, default=1)
def __unicode__(self):
return u'%s' % self.route_id
class Meta:
verbose_name_plural = "Flight Schedule Details"
and the serializer is as below :
class FlightScheduleDetailSerializer(serializers.ModelSerializer):
class Meta:
model = FlightScheduleDetail
fields = '__all__'
class FlightScheduleSerializer(serializers.ModelSerializer):
flight_number_schedule = FlightScheduleDetailSerializer(many=True)
class Meta:
model = FlightSchedule
fields = ['tail_number', 'flight_number', 'origin_port_code', 'destination_port_code', 'flight_departure_time',
'flight_number_schedule']
Here tail_number , flight_number is a foreign key. When I create an API, I get the response as the id of the fields. How can I display the name in the json?
My views.py is as below :
#api_view(['GET'])
def flight_schedule(request):
schedule = FlightSchedule.objects.all()
serializer = FlightScheduleSerializer(schedule, many=True)
return Response(serializer.data)

You can define the source with field_name in your serializer as follows.
I have used source='TailNumber.number'. Please use the right field_name in place of number
class UserProfileSerializer(serializers.ModelSerializer):
tail_number = serializers.CharField(source='TailNumber.number', read_only=True)
flight_number = ....(change as above)
class Meta:
model = FlightSchedule
fields = ['tail_number', 'flight_number', 'origin_port_code', 'destination_port_code', 'flight_departure_time',
'flight_number_schedule']

You could simply add them as if they were attributes.
flight_number_str = serializers.ReadOnlyField(source='flight_number.flight_number')
First flight_number is the attribute of FlightScheduleDetail, then the one of FlightSchedule
and then add it to the list of fields fields = [..., 'flight_number_str']
Otherwise you may have a look at nested relationships in DRF which can offer more possibilities also.

Another alternative is to use the depth option in a serializer. It is to specify nested serialization - doc
class AccountSerializer(serializers.ModelSerializer):
class Meta:
model = Account
fields = ('id', 'account_name', 'users', 'created')
depth = 1
If users is a foreign key or manytomany key the serializer will display the users as an object and not as a key.
The depth option should be set to an integer value that indicates
the depth of relationships that should be traversed before reverting
to a flat representation.