Updated Program.start for search (#272)

- Fixed bug that occurs if no associated course runs have a start datetime
- Updated tests
- Exposed value in search index so that Programs are returned when faceting for availability

ECOM-5316

course_discovery/apps/course_metadata/models.py

@@ -650,9 +650,15 @@ class Program(TimeStampedModel):
     @property
     def start(self):
         """ Start datetime, calculated by determining the earliest start datetime of all related course runs. """
-        if len(self.course_runs) == 0:
-            return None
-        return min([course_run.start for course_run in self.course_runs])
+        course_runs = self.course_runs
+
+        if course_runs:
+            start_dates = [course_run.start for course_run in self.course_runs if course_run.start]
+
+            if start_dates:
+                return min(start_dates)
+
+        return None
 
     @property
     def staff(self):

course_discovery/apps/course_metadata/search_indexes.py

@@ -150,6 +150,7 @@ class ProgramIndex(BaseIndex, indexes.Indexable, OrganizationsMixin):
     card_image_url = indexes.CharField(model_attr='card_image_url', null=True)
     status = indexes.CharField(model_attr='status', faceted=True)
     partner = indexes.CharField(model_attr='partner__short_code', null=True, faceted=True)
+    start = indexes.DateTimeField(model_attr='start', null=True, faceted=True)
 
     def prepare_organizations(self, obj):
         return self.prepare_authoring_organizations(obj) + self.prepare_credit_backing_organizations(obj)

course_discovery/apps/course_metadata/tests/test_models.py

@@ -11,12 +11,13 @@ from django.test import TestCase
 from freezegun import freeze_time
 
 from course_discovery.apps.core.models import Currency
+from course_discovery.apps.core.tests.helpers import make_image_file
 from course_discovery.apps.core.utils import SearchQuerySetWrapper
 from course_discovery.apps.course_metadata.models import (
     AbstractNamedModel, AbstractMediaModel, AbstractValueModel, Course, CourseRun, SeatType,
 )
 from course_discovery.apps.course_metadata.tests import factories
-from course_discovery.apps.core.tests.helpers import make_image_file
+from course_discovery.apps.course_metadata.tests.factories import CourseRunFactory
 from course_discovery.apps.ietf_language_tags.models import LanguageTag
 
 
@@ -310,9 +311,20 @@ class ProgramTests(TestCase):
         self.assertEqual(actual_subjects, expected_subjects)
 
     def test_start(self):
+        """ Verify the property returns the minimum start date for the course runs associated with the
+        program's courses. """
         expected_start = min([course_run.start for course_run in self.course_runs])
         self.assertEqual(self.program.start, expected_start)
 
+        # Verify start is None for programs with no courses.
+        self.program.courses.clear()
+        self.assertIsNone(self.program.start)
+
+        # Verify start is None if no course runs have a start date.
+        course_run = CourseRunFactory(start=None)
+        self.program.courses.add(course_run.course)
+        self.assertIsNone(self.program.start)
+
     def test_price_ranges(self):
         currency = Currency.objects.get(code='USD')
         course_run = factories.CourseRunFactory()