Django Rest Framework - conditionally make serializer's field required or not using other field value

Question

In my DRF project, I have a model:

class Item(BaseModel):
    PRIVATE = 'PRIVATE'
    COMPANY = 'COMPANY'
    ACCOUNT_TYPES = (
        (PRIVATE, _('Private')),
        (COMPANY, _('Company')),
    )
    company_name = models.CharField(max_length=128, null=True, blank=True)
    person_name = models.CharField(max_length=128, null=True, blank=True)
    account_type = models.CharField(max_length=32, choices=ACCOUNT_TYPES)
    phone = models.CharField(max_length=128, null=True, blank=True)
    email = models.EmailField(max_length=128, null=True, blank=True)

and ItemSerializer in serializers like:

class ItemSerializer(serializers.ModelSerializer):
    class Meta:
        model = Item
        fields = ('account_type', 'company_name', 'person_name')

    def create(self, validated_data):
        print('ItemSerializer, create')
        print('validated_data:', validated_data)
        return super().create(validated_data)

    def validate(self, attrs):
        print('ItemSerializer validate, attrs:', attrs)
        return attrs

as you can see in the model, there are fields company_name and person_name, none of them is required in the model.

To create an Item, account_type has to be specified. Its either PRIVATE or COMPANY.

Now, in my serializer I want to make specific fields required if account type is company or private. For example, is account_type is COMPANY, I want to make field company_name required. If account_type is PRIVATE I want to make person_name required.

1. Which method is a proper space to achieve this and how can I do this?
2. Also using above logic I want to do extra validation on the field. Example: is account_type is PRIVATE and person_name is not empty, I want to do some validation on person_name (check if it has a proper format, length etc)

Answer 1

You can use def validate(self, data) to check condition required, and def validate_{field_name}(self, value) for extra validation:

class ItemSerializer(serializers.ModelSerializer):
    class Meta:
        model = Item
        fields = ('account_type', 'company_name', 'person_name')
        extra_kwargs = {
            'company_name': {'required': False},
            'person_name': {'required': False},
        }

    def validate(self, data):
        data_dict = dict(data)
        data_keys = data.keys()
        account_type= data_dict.get('account_type')
        if account_type == 'PRIVATE' and 'person_name' not in data_keys:
            raise serializers.ValidationError('person_name required when account_type is PRIVATE.')
        if account_type == 'COMPANY' and 'company_name' not in data_keys:
            raise serializers.ValidationError('company_name required when account_type is COMPANY.')
        return data

    def validate_person_name(self, value):
        if len(value) < 10:
            raise serializers.ValidationError('person_name must be at least 10 characters.')
        return value

Answer 2

You can use the validate method of the serializer that receives all the serialized fields as parameter, see here.