Django double nested serializer

Question

I am writing an api's application where Order is an entity that provides information about what customers want to buy, one Order can contain different products with different quantity and different prices. The entity that includes this information in Order is called Order Detail.

And I have some problems with double nested serializers.

After post request with:

{
    "external_id": "PR-123-321-123",
    "details": [{
        "product": {"id": 4},
        "amount": 10,
        "price": "12.00"
    }, ... ]
}

I want to get this response:

{
    "id": 1,
    "status": "new",
    "created_at": "2021-01-01T00:00:00",
    "external_id": "PR-123-321-123",
    "details": [{
        "id": 1,
        "product": {"id": 4, "name": "Dropbox"},
        "amount": 10,
        "price": "12.00"
    }, ... ]
}

But now i have some error: "Cannot assign "OrderedDict()": "OrderDetail.product" must be a "Product" instance."

What's wrong?

Models:

from django.db import models


class Order(models.Model):
    STATUS_CHOICES = (
        ('new', 'new'),
        ('accepted', 'accepted'),
        ('failed', 'failed')
    )
    status = models.CharField(max_length=12, choices=STATUS_CHOICES, default='new')
    created_at = models.DateTimeField(auto_now_add=True)
    external_id = models.CharField(max_length=128, unique=True)


class Product(models.Model):
    name = models.CharField(max_length=64)

    def __str__(self):
        return self.name


class OrderDetail(models.Model):
    order = models.ForeignKey(Order, related_name='details', on_delete=models.CASCADE)
    amount = models.IntegerField()
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    price = models.DecimalField(max_digits=8, decimal_places=2)

    def __str__(self):
        return f'{self.order} detail'

Serializers:

from rest_framework import serializers
from rest_framework.serializers import ModelSerializer

from order.models import Order, Product, OrderDetail


class ProductSerializer(ModelSerializer):
    class Meta:
        model = Product
        fields = '__all__'
        read_only_fields = ('name', )


class OrderDetailSerializer(ModelSerializer):
    product = ProductSerializer()

    class Meta:
        model = OrderDetail
        fields = (
            'id',
            'product',
            'amount',
            'price'
        )


class OrderSerializer(ModelSerializer):
    details = OrderDetailSerializer(many=True)
    status = serializers.CharField(source='get_status_display', read_only=True)

    class Meta:
        model = Order
        fields = (
            'id',
            'status',
            'created_at',
            'external_id',
            'details'
        )

    def create(self, validated_data):
        details_data = validated_data.pop('details')
        order = Order.objects.create(**validated_data)
        for detail_data in details_data:
            OrderDetail.objects.create(**detail_data, order=order)
        return order

Nikita Biryukov · Accepted Answer · 2021-06-26 16:18:07Z

1

    def create(self, *args, **kwargs):
        order = Order.objects.create(external_id=self.context.get('request').data.get('external_id'))
        OrderDetail.objects.bulk_create(
            [OrderDetail(**order_detail, order=order, product=Product.objects.get(**order_detail.pop('product')))
             for order_detail in self.context.get('request').data.get('details')]
        )
        return order

answered Jun 26, 2021 at 16:18

Nikita Biryukov

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Comments

Aprimus · Accepted Answer · 2021-06-24 15:35:25Z

0

Modify the OrderSerializer create method, to first retrieve the Product instance before the OrderDetail object is created.

class OrderSerializer(ModelSerializer):
    details = OrderDetailSerializer(many=True)
    status = serializers.CharField(source='get_status_display', read_only=True)

    class Meta:
        model = Order
        fields = (
            'id',
            'status',
            'created_at',
            'external_id',
            'details'
        )

    def create(self, validated_data):
        details_data = validated_data.pop('details')
        order = Order.objects.create(**validated_data)
        for detail_data in details_data:
            try:
                product = Product.objects.get(**detail_data.pop('product'))
                OrderDetail.objects.create(**detail_data, order=order, product=product)
            except (Product.DoesNotExist, Product.MultipleObjectsReturned):
                raise serializers.ValidationError('Your custom error message...')
        return order

edited Jun 24, 2021 at 15:35

answered Jun 24, 2021 at 14:43

Aprimus

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2 Comments

Nikita Biryukov Over a year ago

Thanks, but i got another one error: "MultipleObjectsReturned at /api/v1/orders/ get() returned more than one Product -- it returned 2!"

Nikita Biryukov Over a year ago

And i got except error, because i have one more product. I thought, maybe the problem is that the product is already being used in the order, but I created a new product and indicate it ID in the post request, as described above in the body of the question. Here is the request body where I pass the product id: ``` { "external_id": "PR-123-321-123", "details": [{ "product": {"id": 4}, "amount": 10, "price": "12.00" }] } ```

Rahul Raj · Accepted Answer · 2021-06-26 14:53:16Z

0

class OrderSerializer(serializers.ModelSerializer):
    order = OrderDetailSerializer(many=True, source='order_set', required=False)

    class Meta:
        model = Order
        fields = (
            'id',
            'status',
            'created_at',
            'external_id',
            'details'
        )
 
    def create(self, validated_data):
        if 'order_set' in validated_data:
            order = validated_data.pop('order_set')
        else:
            order = []    
        instance = super().create(validated_data)

        for cd in order:
           instance.order_set.create(**cd)
        return instance

answered Jun 26, 2021 at 14:53

Rahul Raj

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1 Comment

Nikita Biryukov Over a year ago

Thanks, but i have my own solution.

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