Create users as catalog viewers.

course_discovery/apps/api/serializers.py

 from django.contrib.auth import get_user_model
+from django.db import transaction
 from django.utils.translation import ugettext_lazy as _
 from rest_framework import serializers
 
@@ -93,11 +94,31 @@ class CatalogSerializer(serializers.ModelSerializer):
                                            allow_null=True, allow_empty=True, required=False,
                                            help_text=_('Usernames of users with explicit access to view this catalog'))
 
+    def is_valid(self, **kwargs):
+        # Ensure that the catalog's viewers actually exist in the
+        # DB. We keep this in a transaction so that users are only
+        # created if the data is valid.
+        sid = transaction.savepoint()
+        for username in self.initial_data.get('viewers', ()):  # pylint: disable=no-member
+            User.objects.get_or_create(username=username)
+        if super().is_valid(**kwargs):
+            # Data is good; commit the transaction.
+            transaction.savepoint_commit(sid)
+            return True
+        else:
+            # Invalid data; roll back the user creation.
+            transaction.savepoint_rollback(sid)
+            return False
+
     def create(self, validated_data):
+        viewers = set()
+        for username in validated_data.pop('viewers'):
+            user = User.objects.get(username=username)
+            viewers.add(user)
         # Set viewers after the model has been saved
-        viewers = validated_data.pop('viewers')
         instance = super(CatalogSerializer, self).create(validated_data)
         instance.viewers = viewers
+        instance.save()
         return instance
 
     class Meta(object):

course_discovery/apps/api/tests/test_serializers.py

@@ -9,6 +9,7 @@ from course_discovery.apps.api.serializers import(
     PersonSerializer, AffiliateWindowSerializer
 )
 from course_discovery.apps.catalogs.tests.factories import CatalogFactory
+from course_discovery.apps.core.models import User
 from course_discovery.apps.core.tests.factories import UserFactory
 from course_discovery.apps.course_metadata.tests.factories import (
     CourseFactory, CourseRunFactory, SubjectFactory, PrerequisiteFactory,
@@ -36,6 +37,34 @@ class CatalogSerializerTests(TestCase):
         }
         self.assertDictEqual(serializer.data, expected)
 
+    def test_create_new_user(self):
+        username = 'test-user'
+        data = {
+            'viewers': [username],
+            'id': None,
+            'name': 'test new catalog',
+            'query': '*',
+        }
+        self.assertEqual(User.objects.filter(username=username).count(), 0)  # pylint: disable=no-member
+        serializer = CatalogSerializer(data=data)
+        self.assertTrue(serializer.is_valid())
+        catalog = serializer.save()
+        self.assertEqual([viewer.username for viewer in catalog.viewers], [username])
+        self.assertEqual(User.objects.filter(username=username).count(), 1)  # pylint: disable=no-member
+
+    def test_invalid_data_user_create(self):
+        """Verify that users are not created if the serializer data is invalid."""
+        username = 'test-user'
+        data = {
+            'viewers': [username],
+            'id': None,
+            'name': '',
+            'query': '',
+        }
+        serializer = CatalogSerializer(data=data)
+        self.assertFalse(serializer.is_valid())
+        self.assertEqual(User.objects.filter(username=username).count(), 0)  # pylint: disable=no-member
+
 
 class CourseSerializerTests(TestCase):
     def test_data(self):