added validation to UserSerializer

apps/account/models.py

@@ -45,15 +45,19 @@ class UserQuerySet(models.QuerySet):
         return self.filter(is_active=switcher)
 
     def by_oauth2_access_token(self, token):
-        """Find user by access token"""
+        """Find users by access token"""
         return self.filter(oauth2_provider_accesstoken__token=token,
                            oauth2_provider_accesstoken__expires__gt=timezone.now())
 
     def by_oauth2_refresh_token(self, token):
-        """Find user by access token"""
+        """Find users by access token"""
         return self.filter(oauth2_provider_refreshtoken__token=token,
                            oauth2_provider_refreshtoken__expires__gt=timezone.now())
 
+    def by_username(self, username: str):
+        """Filter users by username."""
+        return self.filter(username=username)
+
 
 class User(ImageMixin, AbstractUser):
     """Base user model."""

apps/account/serializers/common.py

@@ -39,6 +39,12 @@ class UserSerializer(serializers.ModelSerializer):
             raise serializers.ValidationError()
         return value
 
+    def validate_username(self, value):
+        """Validate username"""
+        if models.User.objects.by_username(username=value).exists():
+            raise serializers.ValidationError()
+        return value
+
     def update(self, instance, validated_data):
         """
         Override update method