Add content-guard to Distribution.

closes #3970

pulpcore/pulpcore/app/models/publication.py

@@ -202,6 +202,7 @@ class BaseDistribution(Model):
         publication (models.ForeignKey): The current publication associated with
             the distribution.  This is the publication being served by Pulp through
             this relative URL path and settings.
+        content_guard ((models.ForeignKey): An optional content-guard.
     """
 
     name = models.CharField(max_length=255, db_index=True, unique=True)
@@ -210,6 +211,7 @@ class BaseDistribution(Model):
     publication = models.ForeignKey(Publication, null=True, on_delete=models.SET_NULL)
     publisher = models.ForeignKey(Publisher, null=True, on_delete=models.SET_NULL)
     repository = models.ForeignKey(Repository, null=True, on_delete=models.SET_NULL)
+    content_guard = models.ForeignKey('ContentGuard', null=True, on_delete=models.SET_NULL)
 
     class Meta:
         abstract = True

pulpcore/pulpcore/app/serializers/repository.py

@@ -278,6 +278,12 @@ class DistributionSerializer(ModelSerializer):
         queryset=models.Publisher.objects.all(),
         allow_null=True
     )
+    content_guard = DetailRelatedField(
+        required=False,
+        help_text=_('An optional content-guard.'),
+        queryset=models.ContentGuard.objects.all(),
+        allow_null=True
+    )
     publication = RelatedField(
         required=False,
         help_text=_('The publication being served as defined by this distribution'),
@@ -301,7 +307,13 @@ class DistributionSerializer(ModelSerializer):
     class Meta:
         model = models.Distribution
         fields = ModelSerializer.Meta.fields + (
-            'name', 'base_path', 'publisher', 'publication', 'base_url', 'repository',
+            'name',
+            'base_path',
+            'publisher',
+            'publication',
+            'base_url',
+            'repository',
+            'content_guard',
         )
 
     def _validate_path_overlap(self, path):