Django-Rest-Framework. Updating nested object

Question

I'm having a problem of updating a nested object.

So I have a model which structure is similar to this one:

class Invoice(models.Model):     nr = models.CharField(max_length=100)     title = models.CharField(max_length=100)  class InvoiceItem(models.Model):     name = models.CharField(max_length=100)     price = models.FloatField()     invoice = models.ForeignKey(Invoice, related_name='items') 

I need to create child objects from parent, and what I mean by that, is to create InvoiceItems directly when creating an Invoice object. For this purpose, I've wrote the following serializers:

class InvoiceItemSerializer(serializers.ModelSerializer):     invoice = serializers.PrimaryKeyRelatedField(queryset=Invoice.objects.all(), required=False)     class Meta:         model = InvoiceItem   class InvoiceSerializer(serializers.ModelSerializer):     items = InvoiceItemSerializer(many=True)      class Meta:         model = Invoice      def create(self, validated_data):         items = validated_data.pop('items', None)         invoice = Invoice(**validated_data)         invoice.save()         for item in items:             InvoiceItem.objects.create(invoice=invoice, **item)         return invoice 

Up till now, the create/read/delete methods work perfectly, except the update. I think the below logic should be correct, but it misses something.

def update(self, instance, validated_data):     instance.nr = validated_data.get('nr', instance.nr)     instance.title = validated_data.get('title', instance.title)     instance.save()      # up till here everything is updating, however the problem appears here.     # I don't know how to get the right InvoiceItem object, because in the validated     # data I get the items queryset, but without an id.      items = validated_data.get('items')     for item in items:         inv_item = InvoiceItem.objects.get(id=?????, invoice=instance)         inv_item.name = item.get('name', inv_item.name)         inv_item.price = item.get('price', inv_item.price)         inv_item.save()      return instance 

Any help would be really appreciated.

Answer 1

This is the way I've accomplished the task:

I've added an id field to the InvoiceItemSerializer

class InvoiceItemSerializer(serializers.ModelSerializer):     ...     id = serializers.IntegerField(required=False)     ... 

And the update method for the InvoiceSerializer

def update(self, instance, validated_data):     instance.nr = validated_data.get('nr', instance.nr)     instance.title = validated_data.get('title', instance.title)     instance.save()      items = validated_data.get('items')      for item in items:         item_id = item.get('id', None)         if item_id:             inv_item = InvoiceItem.objects.get(id=item_id, invoice=instance)             inv_item.name = item.get('name', inv_item.name)             inv_item.price = item.get('price', inv_item.price)             inv_item.save()         else:             InvoiceItem.objects.create(account=instance, **item)      return instance 

Also in the create method I'm popping the id if it is passed.

Answer 2

All of these solutions seemed too complex or too specific for me, I ended up using code from the tutorial here which was incredibly simple and reusable:

from rest_framework import serializers from django.contrib.auth import get_user_model from myapp.models import UserProfile   # You should already have this somewhere class UserProfileSerializer(serializers.ModelSerializer):     class Meta:         model = UserProfile         fields = ['nested', 'fields', 'you', 'can', 'edit']   class UserSerializer(serializers.ModelSerializer):     # CHANGE "userprofile" here to match your one-to-one field name     userprofile = UserProfileSerializer()      def update(self, instance, validated_data):         # CHANGE "userprofile" here to match your one-to-one field name         if 'userprofile' in validated_data:             nested_serializer = self.fields['userprofile']             nested_instance = instance.userprofile             nested_data = validated_data.pop('userprofile')              # Runs the update on whatever serializer the nested data belongs to             nested_serializer.update(nested_instance, nested_data)          # Runs the original parent update(), since the nested fields were         # "popped" out of the data         return super(UserSerializer, self).update(instance, validated_data) 

EDIT: Bugfix, I added a check for the nested field's existence before attempting to update it.