Use database constraint to prevent relationships with yourself.

fedireads/incoming.py

@@ -128,14 +128,15 @@ def handle_incoming_follow(activity):
     to_follow = models.User.objects.get(actor=activity['object'])
     # figure out who they are
     user = get_or_create_remote_user(activity['actor'])
-    # TODO: allow users to manually approve requests
     try:
         request = models.UserFollowRequest.objects.create(
             user_subject=user,
             user_object=to_follow,
             relationship_id=activity['id']
         )
-    except django.db.utils.IntegrityError:
+    except django.db.utils.IntegrityError as err:
+        if err.__cause__.diag.constraint_name != 'userfollowrequest_unique':
+            raise
         # Duplicate follow request. Not sure what the correct behaviour is, but
         # just dropping it works for now. We should perhaps generate the
         # Accept, but then do we need to match the activity id?

fedireads/migrations/0017_auto_20200314_2152.py

@@ -0,0 +1,26 @@
+# Generated by Django 3.0.3 on 2020-03-14 21:52
+
+from django.db import migrations, models
+import django.db.models.expressions
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('fedireads', '0016_auto_20200313_1337'),
+    ]
+
+    operations = [
+        migrations.AddConstraint(
+            model_name='userblocks',
+            constraint=models.CheckConstraint(check=models.Q(_negated=True, user_subject=django.db.models.expressions.F('user_object')), name='userblocks_no_self'),
+        ),
+        migrations.AddConstraint(
+            model_name='userfollowrequest',
+            constraint=models.CheckConstraint(check=models.Q(_negated=True, user_subject=django.db.models.expressions.F('user_object')), name='userfollowrequest_no_self'),
+        ),
+        migrations.AddConstraint(
+            model_name='userfollows',
+            constraint=models.CheckConstraint(check=models.Q(_negated=True, user_subject=django.db.models.expressions.F('user_object')), name='userfollows_no_self'),
+        ),
+    ]

fedireads/models/user.py

@@ -95,6 +95,10 @@ class UserRelationship(FedireadsModel):
             models.UniqueConstraint(
                 fields=['user_subject', 'user_object'],
                 name='%(class)s_unique'
+            ),
+            models.CheckConstraint(
+                check=~models.Q(user_subject=models.F('user_object')),
+                name='%(class)s_no_self'
             )
         ]