Use database constraint to prevent relationships with yourself.

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'),
+        ),
+    ]