Django REST Framework create and update nested objects - django

Question

I am trying to create or update a nested object if the object exists, I tried to use the create_or_update method, now the create works fine, but the update failed and said the pk already existed.
My Model:
class ContentHotel(models.Model):
hotel_id = models.IntegerField(unique=True, blank=True, primary_key=True)
star = models.FloatField(blank=True, null=True)
class Meta:
managed = False
db_table = 'content_hotels'
ordering = ('hotel_id',)
def __str__(self):
return str(self.hotel_id)
class RateHotel(models.Model):
rate_hotel_id = models.IntegerField(blank=True, unique=True, primary_key=True)
content_hotel = models.ForeignKey(ContentHotel, on_delete=models.CASCADE, related_name='rate_hotels')
source_code = models.CharField(max_length=20, blank=True, null=True)
class Meta:
managed = False
db_table = 'rate_hotels'
ordering = ('rate_hotel_id',)
def __str__(self):
return str(self.rate_hotel_id)
My Serializers:
# To handle RateHotel object operations
class RateHotelSerializer(serializers.ModelSerializer):
class Meta:
model = RateHotel
fields = __all__
# To handle nested object operations
class RateHotelSerializerTwo(serializers.ModelSerializer):
class Meta:
model = RateHotel
fields = __all__
read_only_fields = ('content_hotel',)
class ContentHotelSerializer(serializers.ModelSerializer):
rate_hotels = RateHotelSerializerTwo(many=True)
class Meta:
model = ContentHotel
fields = __all__
def create(self, validated_data):
rate_hotels_data = validated_data.pop('rate_hotels')
hotel_id = validated_data.pop('hotel_id')
content_hotel, created = ContentHotel.objects.update_or_create(hotel_id=hotel_id, defaults={**validated_data})
for rate_hotel_data in rate_hotels_data:
rate_hotel_id = rate_hotel_data.pop('rate_hotel_id')
RateHotel.objects.update_or_create(rate_hotel_id=rate_hotel_id, content_hotel=content_hotel,
defaults=rate_hotel_data)
return content_hotel
def update(self, instance, validated_data):
rate_hotels_data = validated_data.pop('rate_hotels')
rate_hotels = list(instance.rate_hotels.all())
for key in validated_data:
instance.key = validated_data.get(key, instance.key)
instance.save()
for rate_hotel_data in rate_hotels_data:
rate_hotel = rate_hotels.pop(0)
for key in rate_hotel_data:
rate_hotel.key = rate_hotel_data.get(key, rate_hotel.key)
rate_hotel.save()
return instance
JSON:
# Post Request - Create:
{
"hotel_id": -1,
"star": null,
"rate_hotels": [{"rate_hotel_id": -1}]
}
# Post Response:
{
"hotel_id": -1,
"star": null,
"rate_hotels": [
{
"content_hotel": -1,
"rate_hotel_id": -1,
"source_code": null,
}
]
}
# Post Request - Update:
{
"hotel_id": -1,
"star": 2,
"rate_hotels": [{"rate_hotel_id": -1, "source_code": "-1"}]
}
{
"hotel_id": [
"content hotel with this hotel id already exists."
],
"rate_hotels": [
{
"rate_hotel_id": [
"rate hotel with this rate hotel id already exists."
]
}
],
"status_code": 400
}
If I send a put request to update the nested object, the content hotel part works correctly, but the rate hotel part still said 'rate_hotel_id' already exists.
Can anyone help me fix this issue? I cannot find any related source online, thanks in advance!

Answer 1

Hmmmm, this looks like you could be looking for for "update if exists else create" use case, and Django has a get_or_create() method for performing what you want, see the docs here for reference: https://docs.djangoproject.com/en/dev/ref/models/querysets/#get-or-create
However, for you it could look something like this:
id = 'some identifier that is unique to the model you wish to lookup'
content_hotel, created = RateHotel.objects.get_or_create(
rate_hotel_id=rate_hotel_id,
content_hotel=content_hotel,
defaults=rate_hotel_data
)
if created:
# means you have created a new content hotel, redirect a success here or whatever you want to do on creation!
else:
# content hotel just refers to the existing one, this is where you can update your Model
I would also advise removing the hotel_id and hotel_rate_id as primary keys:
class ContentHotel(models.Model):
hotel_id = models.IntegerField(unique=True, blank=True,)
star = models.FloatField(blank=True, null=True)
class Meta:
managed = False
db_table = 'content_hotels'
ordering = ('hotel_id',)
def __str__(self):
return str(self.hotel_id)
class RateHotel(models.Model):
rate_hotel_id = models.IntegerField(blank=True, unique=True,)
content_hotel = models.ForeignKey(ContentHotel, on_delete=models.CASCADE, related_name='rate_hotels')
source_code = models.CharField(max_length=20, blank=True, null=True)
class Meta:
managed = False
db_table = 'rate_hotels'
ordering = ('rate_hotel_id',)
def __str__(self):
return str(self.rate_hotel_id)
The update_or_create() method does not accept a primary key, but can accept other unique database fields to perform the update:
So, an update_or_create() would look like so:
obj, created = Person.objects.update_or_create(
first_name='John', last_name='Lennon',
defaults={'first_name': 'Bob'},
)

Answer 2

Your create code looks fine, but there are some bigger issues with your update code which you need to address before we can know where the real issue lies I think.
for key in validated_data:
instance.key = validated_data.get(key, instance.key)
instance.save()
Here you are trying to loop through the values in the validated data and assign the values of that key to that attribute on the model. What you are actually doing is setting the attribute key on the model to the value of each key in validated_data. To better illustrate the issue I'll give you an example which corrects the issue:
for key in validated_data:
setattr(instance, key, validated_data.get(key, getattr(instance, key))
instance.save()
Here rather than trying to set instance.key we use the python built-in method setattr to set the attribute with the name that matches the value of the variable key to the value which we pull from validated_data.
I'm not sure correcting this will solve your issue though. I'd make sure you're correctly sending your request to the correct url with the proper header values to get to the update method. It could be that Django Rest Framework is preventing the creation behind the scenes because it thinks you're sending the request as a create operation and it finds the primary keys already.