How to change "This field is required" error message for a DjangoRestFramework serializer?

Question

When the user submits a form to the back end passing a JSON user object, this is the view which handles it:

class user_list(APIView):
    """
    Create a new user.
    """

    def post(self, request):
        serializer = UserSerializer(data=request.DATA)
        if serializer.is_valid():
            serializer.save()
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)

My issue is, if the user does not fill in a certain field in the form, the error message which DRF sends to the front end is "This field is required". Is there a way for me to change it so that for all fields, the error message is "{ fieldname } is required."?

This is my serializers.py:

from rest_framework import serializers
from django.contrib.auth.models import User
from CMSApp.mixins import SetCustomErrorMessagesMixin

from django.utils.translation import gettext as _
from rest_framework.validators import UniqueValidator
from django.core.validators import RegexValidator


class UserSerializer(SetCustomErrorMessagesMixin, serializers.ModelSerializer):

    class Meta:
        model = User
        fields = ('username', 'password', 'email', 'userextended')

        extra_kwargs = {
                    'password': {
                        'write_only': True,
                    }
                }

        custom_error_messages_for_validators = {
            'username': {
                UniqueValidator: _('This username is already taken. Please try again.'),
                RegexValidator: _('Invalid username')
            }
        }

    def create(self, validated_data):
        user = User.objects.create_user(
            email = validated_data['email'],
            username = validated_data['username'],
            password = validated_data['password'],
        )
        return user

and this is SetCustomErrorMessageMixin:

class SetCustomErrorMessagesMixin:
    """
    Replaces built-in validator messages with messages, defined in Meta class. 
    This mixin should be inherited before the actual Serializer class in order to call __init__ method.

    Example of Meta class:

    >>> class Meta:
    >>>     model = User
    >>>     fields = ('url', 'username', 'email', 'groups')
    >>>     custom_error_messages_for_validators = {
    >>>         'username': {
    >>>             UniqueValidator: _('This username is already taken. Please, try again'),
    >>>             RegexValidator: _('Invalid username')
    >>>         }
    >>>     }
    """
    def __init__(self, *args, **kwargs):
        # noinspection PyArgumentList
        super(SetCustomErrorMessagesMixin, self).__init__(*args, **kwargs)
        self.replace_validators_messages()

    def replace_validators_messages(self):
        for field_name, validators_lookup in self.custom_error_messages_for_validators.items():
            # noinspection PyUnresolvedReferences
            for validator in self.fields[field_name].validators:
                if type(validator) in validators_lookup:
                    validator.message = validators_lookup[type(validator)]

    @property
    def custom_error_messages_for_validators(self):
        meta = getattr(self, 'Meta', None)
        return getattr(meta, 'custom_error_messages_for_validators', {})

Lastly, this is my models.py (the UserExtended model):

from django.db import models
from django.contrib.auth.models import User

# Create your models here.

class Color(models.Model):
    colorName = models.CharField(max_length=50, unique=True)
    colorCode = models.CharField(max_length=10, unique=True)

class UserExtended(models.Model):
    user = models.OneToOneField(User, related_name="userextended")
    color = models.ForeignKey(Color)

Answer 1

You can override the __init__() method of UserSerializer to change the default error message for a required field .

We will iterate over the fields of the serializer and change the value of default error_messagesvalue for the required key.

class UserSerializer(SetCustomErrorMessagesMixin, serializers.ModelSerializer):

    def __init__(self, *args, **kwargs):
        super(UserSerializer, self).__init__(*args, **kwargs) # call the super() 
        for field in self.fields: # iterate over the serializer fields
            self.fields[field].error_messages['required'] = '%s field is required'%field # set the custom error message

    ...