Fix username validation to check edx_username (#2869)

Author: rhysyngsun

users/serializers.py

@@ -19,6 +19,7 @@
 from main.constants import USER_REGISTRATION_FAILED_MSG
 from openedx.api import validate_username_email_with_edx
 from openedx.exceptions import EdxApiRegistrationValidationException
+from openedx.models import OpenEdxUser
 from openedx.tasks import change_edx_user_email_async
 from users.models import ChangeEmailRequest, LegalAddress, User, UserProfile
 
@@ -273,7 +274,7 @@ def validate(self, data):
             # Local duplicate check
             if (
                 not self.instance
-                and User.objects.filter(username__iexact=username).exists()
+                and OpenEdxUser.objects.filter(edx_username__iexact=username).exists()
             ):
                 raise serializers.ValidationError(
                     {

users/serializers_test.py

@@ -203,7 +203,7 @@ def test_username_validation(
         status=status.HTTP_200_OK,
     )
     # Seed an initial user with a constant username
-    UserFactory.create(username=USERNAME)
+    UserFactory.create(openedx_user__edx_username=USERNAME)
     serializer = UserSerializer(
         data={
             "username": new_username,
@@ -236,7 +236,7 @@ def test_username_validation_exception(user, settings, valid_address_dict):
         status=status.HTTP_200_OK,
     )
     # Seed an initial user with a constant username
-    UserFactory.create(username=USERNAME)
+    UserFactory.create(openedx_user__edx_username=USERNAME)
     serializer = UserSerializer(
         data={
             "username": user.edx_username,