class ProductImageSerializer(serializers.ModelSerializer):
    class Meta:
        model = ProductImage
        fields = ('product', 'image_id', 'url',)


class ProductSerializer(serializers.ModelSerializer):
    images = ProductImageSerializer(many=True, read_only=True)

    class Meta:
        model = Product
        fields = ('product_id', 'title', 'images',)

    def create(self, validated_data):
        images_data = validated_data.pop("images", [])  # an empty list by default
        product = Product.objects.create(**validated_data)
        for image_data in images_data:
            ProductImage.objects.create(product=product, **image_data)

        return product

    def update(self, instance, validated_data):
        request = self.context['request']

        instance.title = validated_data.get('title', instance.title)

        new_images_data = request.data.get("images")
        new_images_ids = [image.get("image_id") for image in new_images_data]
        
        old_images = instance.images.all()
        for old_image in old_images:  # deleting unselected images
            if old_image.image_id not in new_images_ids:
                old_image.delete()

        for new_image_data in new_images_data:
            ProductImage.objects.update_or_create(**new_image_data)

        instance.save()
        return instance