Deleting orphaned media and people models after loading data

ECOM-4266

course_discovery/apps/core/tests/test_utils.py

+from django.db import models
+from django.test import TestCase
+
+from course_discovery.apps.core.utils import get_all_related_field_names
+
+
+class UnrelatedModel(models.Model):
+    class Meta:
+        app_label = 'core'
+        managed = False
+
+
+class RelatedModel(models.Model):
+    class Meta:
+        app_label = 'core'
+        managed = False
+
+
+class ForeignRelatedModel(models.Model):
+    fk = models.ForeignKey(RelatedModel)
+
+    class Meta:
+        app_label = 'core'
+        managed = False
+
+
+class M2MRelatedModel(models.Model):
+    m2m = models.ManyToManyField(RelatedModel)
+
+    class Meta:
+        app_label = 'core'
+        managed = False
+
+
+class ModelUtilTests(TestCase):
+    def test_get_all_related_field_names(self):
+        """ Verify the method returns the names of all relational fields for a model. """
+        self.assertEqual(get_all_related_field_names(UnrelatedModel), [])
+        self.assertEqual(set(get_all_related_field_names(RelatedModel)), {'foreignrelatedmodel', 'm2mrelatedmodel'})

course_discovery/apps/core/utils.py

@@ -28,3 +28,33 @@ class ElasticsearchUtils(object):
             }
             es.indices.update_aliases(body)
             logger.info('...alias updated.')
+
+
+def get_all_related_field_names(model):
+    """
+    Returns the names of all related fields (e.g. ForeignKey ManyToMany)
+
+    Args:
+        model (Model): Model whose field names should be returned
+
+    Returns:
+        list[str]
+    """
+    fields = model._meta._get_fields(forward=False)  # pylint: disable=protected-access
+    names = set([field.name for field in fields])
+    return list(names)
+
+
+def delete_orphans(model):
+    """
+    Deletes all instances of the given model with no relationships to other models.
+
+    Args:
+        model (Model): Model whose instances should be deleted
+
+    Returns:
+        None
+    """
+    field_names = get_all_related_field_names(model)
+    kwargs = {'{0}__isnull'.format(field_name): True for field_name in field_names}
+    model.objects.filter(**kwargs).delete()

course_discovery/apps/course_metadata/data_loaders.py

@@ -4,13 +4,14 @@ import logging
 from decimal import Decimal
 from urllib.parse import urljoin
 
+import html2text
 from dateutil.parser import parse
 from django.conf import settings
 from edx_rest_api_client.client import EdxRestApiClient
-import html2text
 from opaque_keys.edx.keys import CourseKey
 
 from course_discovery.apps.core.models import Currency
+from course_discovery.apps.core.utils import delete_orphans
 from course_discovery.apps.course_metadata.models import (
     Course, CourseOrganization, CourseRun, Image, LanguageTag, LevelType, Organization, Person, Seat, Subject, Video
 )
@@ -88,6 +89,12 @@ class AbstractDataLoader(metaclass=abc.ABCMeta):
         course_run_key = CourseKey.from_string(course_run_key_str)
         return '{org}+{course}'.format(org=course_run_key.org, course=course_run_key.course)
 
+    @classmethod
+    def delete_orphans(cls):
+        """ Remove orphaned objects from the database. """
+        for model in (Image, Person, Video):
+            delete_orphans(model)
+
 
 class OrganizationsApiDataLoader(AbstractDataLoader):
     """ Loads organizations from the Organizations API. """
@@ -116,6 +123,8 @@ class OrganizationsApiDataLoader(AbstractDataLoader):
 
         logger.info('Retrieved %d organizations from %s.', count, self.api_url)
 
+        self.delete_orphans()
+
     def update_organization(self, body):
         image = None
         image_url = body['logo']
@@ -157,6 +166,8 @@ class CoursesApiDataLoader(AbstractDataLoader):
 
         logger.info('Retrieved %d course runs from %s.', count, self.api_url)
 
+        self.delete_orphans()
+
     def update_course(self, body):
         # NOTE (CCB): Use the data from the CourseKey since the Course API exposes display names for org and number,
         # which may not be unique for an organization.
@@ -238,9 +249,10 @@ class DrupalApiDataLoader(AbstractDataLoader):
             course = self.update_course(cleaned_body)
             self.update_course_run(course, cleaned_body)
 
-        # Clean up orphan data on the end of many-to-many relationships
-        Person.objects.filter(courses_staffed=None).delete()
+        # Clean Organizations separately from other orphaned instances to avoid removing all orgnaziations
+        # after an initial data load on an empty table.
         Organization.objects.filter(courseorganization__isnull=True).delete()
+        self.delete_orphans()
 
         logger.info('Retrieved %d course runs from %s.', len(data), self.api_url)
 
@@ -370,6 +382,8 @@ class EcommerceApiDataLoader(AbstractDataLoader):
 
         logger.info('Retrieved %d course seats from %s.', count, self.api_url)
 
+        self.delete_orphans()
+
     def update_seats(self, body):
         course_run_key = body['id']
         try:

course_discovery/apps/course_metadata/tests/test_data_loaders.py

@@ -17,7 +17,9 @@ from course_discovery.apps.course_metadata.data_loaders import (
 from course_discovery.apps.course_metadata.models import (
     Course, CourseOrganization, CourseRun, Image, LanguageTag, Organization, Person, Seat, Subject
 )
-from course_discovery.apps.course_metadata.tests.factories import CourseRunFactory, SeatFactory
+from course_discovery.apps.course_metadata.tests.factories import (
+    CourseRunFactory, SeatFactory, ImageFactory, PersonFactory, VideoFactory
+)
 
 ACCESS_TOKEN = 'secret'
 COURSES_API_URL = 'https://lms.example.com/api/courses/v1'
@@ -53,6 +55,14 @@ class AbstractDataLoaderTest(TestCase):
         dt = datetime.datetime.utcnow()
         self.assertEqual(AbstractDataLoader.parse_date(dt.isoformat()), dt)
 
+    def test_delete_orphans(self):
+        """ Verify the delete_orphans method deletes orphaned instances. """
+        instances = (ImageFactory(), PersonFactory(), VideoFactory(),)
+        AbstractDataLoader.delete_orphans()
+
+        for instance in instances:
+            self.assertFalse(instance.__class__.objects.filter(pk=instance.pk).exists())  # pylint: disable=no-member
+
 
 class DataLoaderTestMixin(object):
     api_url = None
@@ -371,18 +381,20 @@ class CoursesApiDataLoaderTests(DataLoaderTestMixin, TestCase):
 @override_settings(MARKETING_API_URL=MARKETING_API_URL)
 @ddt.ddt
 class DrupalApiDataLoaderTests(DataLoaderTestMixin, TestCase):
-
-    EXISTING_COURSE_AND_RUN_DATA = ({
-        'course_run_key': 'course-v1:SC+BreadX+3T2015',
-        'course_key': 'SC+BreadX',
-        'title': 'Bread Baking 101',
-        'current_language': 'en-us',
-    }, {
-        'course_run_key': 'course-v1:TX+T201+3T2015',
-        'course_key': 'TX+T201',
-        'title': 'Testing 201',
-        'current_language': ''
-    })
+    EXISTING_COURSE_AND_RUN_DATA = (
+        {
+            'course_run_key': 'course-v1:SC+BreadX+3T2015',
+            'course_key': 'SC+BreadX',
+            'title': 'Bread Baking 101',
+            'current_language': 'en-us',
+        },
+        {
+            'course_run_key': 'course-v1:TX+T201+3T2015',
+            'course_key': 'TX+T201',
+            'title': 'Testing 201',
+            'current_language': ''
+        }
+    )
 
     # A course which exists, but has no associated runs
     EXISTING_COURSE = {