python - Django Rest Framework model Id field in nested relationship serializer

Question

I'm usign Django Rest Framework where I have the following two serializers:

class ServiceSerializer(serializers.ModelSerializer):
    id = serializers.ReadOnlyField()

    class Meta:
        model = ServiceType
        fields = ('id', 'serviceName', 'servicePrice')


class CompanyShortListSerializer(serializers.ModelSerializer):

     services = ServiceSerializer(many=True)

     class Meta:
         model = Company
         fields = ( 'id','name','address','cost_per_patient','cost_per_month','renting_fee','services')

The ServiceType model looks like this:

class ServiceType(models.Model):
     serviceName = EncryptedCharField(max_length=100, blank=True, verbose_name = "Typ us?ugi")
     servicePrice = EncryptedFloatField(null=True, blank=True, verbose_name = "Cena us?ugi", validators = [MinValueValidator(0.1), MaxValueValidator(999)])
     company = models.ForeignKey(Company, related_name = 'services')

I would like to update the existing instances by changing the related services (e.g. deleting some of them). To achieve this I'm doing this:

def update(self, instance, validated_data):
    # Updates an exisitng Company with several services 
    instance.name = validated_data['name']
    instance.address = validated_data['address']
    instance.cost_per_patient = validated_data['cost_per_patient']
    instance.renting_fee = validated_data['renting_fee']
    services_data = validated_data['services']

    for item in services_data:
        updatedService = ServiceType(
            serviceName = item['serviceName'],
            servicePrice = item['servicePrice'],
            id=item['id'], 
            company=instance)
        updatedService.save()

    return instance

The problem that I'm facing is that the service['id'] field is not provided - which means I get a KeyError 'id' - although I added it explicitly in the ServiceSerializer id field.

EDIT

Here's an exemplary request (taken from Chrome) that I'm posting:

 { "id":49,"name":"Test 1",
   "address":"Testowa 1",
   "renting_fee":200,
   "cost_per_month":300,
   "cost_per_patient":null,
   "services":[
   {"id":67,"serviceName":"Terapia","servicePrice":100},
   {"id":68,"serviceName":"Terapia par","servicePrice":150},
   {"id":69,"serviceName":"Terapia po angielsku","servicePrice":120}
   ]
 } 

What am I doing wrong and how to get the ID of a an object(basically ServiceSerializer) using nested serializers?

EDIT no.2

When I print from the serializer update function I get the following:

print(self.data['services']) gives me:

[
 OrderedDict([('id', 67), ('serviceName', u'Terapia'), ('servicePrice', 100.0)]),
 OrderedDict([('id', 68), ('serviceName', u'Terapia par'), ('servicePrice', 150.0)]),
 OrderedDict([('id', 69), ('serviceName', u'Terapia po angielsku'), ('servicePrice', 120.0)]), 
 OrderedDict([('id', 70), ('serviceName', u'Terapia grupowa'), ('servicePrice', 140.0)])
]

However, print(services_data) gives the following (basically the same, but without the id):

[
OrderedDict([(u'serviceName', u'Terapia'), (u'servicePrice', 100.0)]),
OrderedDict([(u'serviceName', u'Terapia par'), (u'servicePrice', 150.0)]),
OrderedDict([(u'serviceName', u'Terapia po angielsku'), (u'servicePrice', 120.0)])
]

And the ids get lost ...

EDIT no.3

According to the Django Rest Framework docs If certain field will be shall be in the serializer output representation it should be a HiddenField. This however requires a default value ... I have checked that and indeed using this HiddenField with a default value 'solves' the problem - the ID is there in validated_data. The problem is that the id is not correct. Is there a possibility to set this id to the value of the object sent to the serializer?

Answer 1

Ok - I think I found the answer after ... carefully reading the docs :)

So according to the docs the id field could be set to a ModelField like this:

id = serializers.ModelField(model_field=ServiceType()._meta.get_field('id'))

Indeed, after adding this line the id field is present in validated_data :)