display name uniqueness

frontend/migrations/0002_userprofile_display_name_unique.py

@@ -0,0 +1,15 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("frontend", "0001_userprofile"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="userprofile",
+            name="display_name",
+            field=models.CharField(max_length=150, unique=True),
+        ),
+    ]

frontend/models.py

@@ -10,7 +10,7 @@ class UserProfile(models.Model):
         on_delete=models.CASCADE,
         related_name="profile",
     )
-    display_name = models.CharField(max_length=150)
+    display_name = models.CharField(max_length=150, unique=True)
 
     def __str__(self):
         return f"{self.display_name} ({self.user.username})"  # type: ignore[attr-defined]

frontend/views.py

@@ -53,6 +53,14 @@ def register(request: HttpRequest) -> HttpResponse:
         if email and User.objects.filter(username=email).exists():
             errors.append("An account with that email already exists.")
 
+        if (
+            display_name
+            and UserProfile.objects.filter(  # type: ignore[attr-defined]
+                display_name=display_name
+            ).exists()
+        ):
+            errors.append("That display name is already taken.")
+
         if errors:
             for error in errors:
                 messages.error(request, error)