Prevent double active infractions with constraint

https://github.com/python-discord/site/issues/273

This commits adds a UniqueConstraint for active infractions on a
combination of the `user` and `type` field. This means that a user
can only have one active infraction of a given type in the database
at any time.

I've also added tests to make sure that this behaves as expected.

1 files changed, 17 insertions, 0 deletions

diff --git a/pydis_site/apps/api/migrations/0045_add_infractions_unique_constraints_active.py b/pydis_site/apps/api/migrations/0045_add_infractions_unique_constraints_active.py
new file mode 100644
index 00000000..bacb56b8
--- /dev/null
+++ b/pydis_site/apps/api/migrations/0045_add_infractions_unique_constraints_active.py
@@ -0,0 +1,17 @@
+# Generated by Django 2.2.6 on 2019-10-07 18:27
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0044_active_infractions_migration'),
+    ]
+
+    operations = [
+        migrations.AddConstraint(
+            model_name='infraction',
+            constraint=models.UniqueConstraint(condition=models.Q(active=True), fields=('user', 'type'), name='unique_active_infraction_per_type_per_user'),
+        ),
+    ]