Skip user-condition validation when the auth table is missing

flags/conditions/validators.py

@@ -3,6 +3,7 @@
 from django.contrib.auth import get_user_model
 from django.core.exceptions import ValidationError
 from django.core.validators import RegexValidator
+from django.db import OperationalError, ProgrammingError
 from django.utils import dateparse
 
 from flags.utils import strtobool
@@ -45,6 +46,13 @@ def validate_user(value):
         UserModel.objects.get(**{UserModel.USERNAME_FIELD: value})
     except UserModel.DoesNotExist as err:
         raise ValidationError("Enter the username of a valid user.") from err
+    except (OperationalError, ProgrammingError):
+        # The user table may not exist yet, for example when the system checks
+        # run during a migration against a fresh database (before the auth
+        # tables are created). The username cannot be checked in that case, so
+        # skip validation rather than letting the database error abort the
+        # migration.
+        pass
 
 
 def validate_date(value):

flags/tests/test_conditions_validators.py

@@ -1,5 +1,8 @@
+from unittest import mock
+
 from django.contrib.auth import get_user_model
 from django.core.exceptions import ValidationError
+from django.db import OperationalError, ProgrammingError
 from django.test import TestCase, override_settings
 
 from flags.conditions.validators import (
@@ -82,6 +85,19 @@ def test_custom_user_invalid(self):
         with self.assertRaises(ValidationError):
             validate_user("nottestuser")
 
+    def test_user_table_missing_is_skipped(self):
+        # If the user table does not exist yet (for example when the system
+        # checks run during a migration against a fresh database), the lookup
+        # raises a database error. Validation should be skipped rather than
+        # letting that error abort the migration. See GH-96.
+        User = get_user_model()
+        for exc in (OperationalError, ProgrammingError):
+            with mock.patch.object(
+                User.objects, "get", side_effect=exc("relation does not exist")
+            ):
+                # Must not raise.
+                validate_user("testuser")
+
 
 class ValidateDateTestCase(TestCase):
     def test_invalid_date_strings(self):