Python use args and kwargs to validate data inside a serializer

Question

Well I am building this django rest api where my users can send some data and I save them into the db. There I need to validate the data send by them prior to saving them to the db.

I have already added validators like,

def validate(self, value):
    UnitOfMeasureName = ["Each", "Grams", "Ounces", "Pounds", "Kilograms", "Metric Tons"]
    if value in UnitOfMeasureName:
        return True
    else:
        return ValidationError('Invalid')

inside the serializers but there are several such validations to be achieved for each serializer. So I am searching for a way where I can use one function for all those validations. I am thinking of using of args and kwargs but have no idea how to proceed. I was thinking something like:

def validate_all(*args, **kwargs):
    if not validation_1:
        validation_error = {add the error messsage to the dic}
    if not validation_2:
        ...
    if not validation_3:
        ...
    return validation_error

An example serializer:

class TransSerializer(serializers.ModelSerializer):
    def validate(self, data):
        if not data['unitofmeasurename'] in UnitOfMeasureName:
            raise serializers.ValidationError("INVALID")
        return data

    class Meta:
        model = Trans
        fields = ('unitofmeasurename','name')

So in another serializer I need to check the validation for both 'unitofmeasurename' and 'name'. Is there a way to achieve this using only one common function? Any ideas please. Thanks in advance.

Probably you can do something like this: https://stackoverflow.com/a/49725843/641249 — neverwalkaloner, Apr 09 '18 at 05:27

inmate_37 · Accepted Answer · 2018-04-09T06:13:25.947

You can do something like:

models

from your_app.mixins import ValidationMixin

class YourSerializer(ModelSerializer, ValidationMixin):

    def create(self, validated_data):
        # First check
        self.raise_if_something_wrong(validated_data['value'])

        # Second check
        self.get_object_if_exist(validated_data['title'])

        # This will happen ONLY if your previous check's were ok
        your_model = YourModel.objects.create(
            **validated_data
        )
        return your_model

mixins

from django.conf import settings
from rest_framework.serializers import ValidationError

class ValidationMixin:

    def raise_if_something_wrong(self, value):
        if value not in settings.UNIT_OF_MEASURE_NAME:
            raise ValidationError(
                'Invalid'
            )
        else:
            pass

    def get_object_if_exist(self, obj_title):
        try:
            return YourModel.objects.get(title=obj_title)
        except YourModel.DoesNotExist:
            raise ValidationError(
                'Cant get that object'
            )

settings

Also add this to your project's main settings.py file, keep it like a tuple:

UNIT_OF_MEASURE_NAME = (
    'Each',
    'Grams',
    'Ounces',
    'Pounds',
    'Kilograms',
    'Metric Tons'
)

As a result you will be able to use ValidationMixin wherever you want to validate data, and keep validation logic in one place.

so what you are suggesting is to add several such **mixins** for each validation I need to achieve? — Pabasara Ranathunga, Apr 09 '18 at 06:03
No, use just one Mixin, but add additional functions inside that Mixin and you are ready to go — inmate_37, Apr 09 '18 at 06:04
It's a dict of parameters that you are passing with request: [Serializers](http://www.django-rest-framework.org/api-guide/serializers/). — inmate_37, Apr 09 '18 at 07:03

Python use args and kwargs to validate data inside a serializer

1 Answers1