Anchor DLC purchases to a base game instead of a parent purchase

Add-on purchases (DLC, Season Pass, Battle Pass) previously linked to a
parent *purchase* via the `related_purchase` self-FK. When the base game
was bought inside a multi-game purchase (e.g. a bundle), there was no
per-game purchase to point at — only the whole bundle.

Replace it with a `related_game` FK (Game -> Game): an add-on belongs to
a *game*, which is unambiguous regardless of how the base game was bought.

- models: drop `related_purchase`; add `related_game`
  (SET_NULL, related_name="addon_purchases"); require it for non-GAME
  types in `save()`.
- forms: replace the parent-purchase picker with a flat `related_game`
  game search (reusing SearchSelectWidget/_game_options); drop the now
  unused related_purchase_queryset/RelatedPurchaseChoiceField.
- views/urls: remove the obsolete related_purchase_by_game endpoint.
- add_purchase.js: drop the parent-dropdown refetch; keep platform
  auto-fill; retarget the type toggle to #id_related_game.
- migration 0020: add -> backfill (related_game = parent's first game by
  sort_name) -> remove related_purchase.
- tests: model validation unit tests + an e2e test for the flat picker.

related_game is deliberately game->game so it can later be synced from
IGDB's parent_game without schema changes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

games/forms.py

@@ -1,6 +1,5 @@
 from django import forms
 from django.db import transaction
-from django.db.models import OuterRef, Subquery
 
 from common.components import (
     DEFAULT_PREFETCH,
@@ -228,31 +227,6 @@ class SessionForm(PrimitiveWidgetsMixin, forms.ModelForm):
         return session
 
 
-def related_purchase_queryset():
-    """GAME purchases annotated with their first game's name.
-
-    Rendering the ``related_purchase`` ``<select>`` calls ``str()`` on every
-    option, and ``Purchase.__str__`` falls back to ``first_game`` — one extra
-    query per option (700+ on a large library). Annotating the first game's
-    name via a subquery lets the choice field build labels without those
-    per-row queries.
-    """
-    first_game_name = Subquery(
-        Game.objects.filter(purchases=OuterRef("pk")).order_by("id").values("name")[:1]
-    )
-    return Purchase.objects.filter(type=Purchase.GAME).annotate(
-        _first_game_name=first_game_name
-    )
-
-
-class RelatedPurchaseChoiceField(forms.ModelChoiceField):
-    def label_from_instance(self, obj) -> str:
-        # Mirrors Purchase.standardized_name but reads the annotated first-game
-        # name instead of querying first_game per option.
-        name = obj.name or getattr(obj, "_first_game_name", None)
-        return name or obj.standardized_name
-
-
 class PurchaseForm(PrimitiveWidgetsMixin, forms.ModelForm):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
@@ -272,9 +246,12 @@ class PurchaseForm(PrimitiveWidgetsMixin, forms.ModelForm):
             search_url="/api/platforms/search", options_resolver=_platform_options
         ),
     )
-    related_purchase = RelatedPurchaseChoiceField(
-        queryset=related_purchase_queryset(),
+    related_game = forms.ModelChoiceField(
+        queryset=Game.objects.order_by("sort_name"),
         required=False,
+        widget=SearchSelectWidget(
+            search_url="/api/games/search", options_resolver=_game_options
+        ),
     )
 
     price_currency = forms.CharField(
@@ -305,14 +282,14 @@ class PurchaseForm(PrimitiveWidgetsMixin, forms.ModelForm):
             "price_currency",
             "ownership_type",
             "type",
-            "related_purchase",
+            "related_game",
             "name",
         ]
 
     def clean(self):
         cleaned_data = super().clean()
         purchase_type = cleaned_data.get("type")
-        related_purchase = cleaned_data.get("related_purchase")
+        related_game = cleaned_data.get("related_game")
         name = cleaned_data.get("name")
 
         # Set the type on the instance to use get_type_display()
@@ -321,10 +298,10 @@ class PurchaseForm(PrimitiveWidgetsMixin, forms.ModelForm):
 
         if purchase_type != Purchase.GAME:
             type_display = self.instance.get_type_display()
-            if not related_purchase:
+            if not related_game:
                 self.add_error(
-                    "related_purchase",
-                    f"{type_display} must have a related purchase.",
+                    "related_game",
+                    f"{type_display} must have a related game.",
                 )
             if not name:
                 self.add_error("name", f"{type_display} must have a name.")

games/migrations/0020_remove_purchase_related_purchase_and_more.py

@@ -0,0 +1,46 @@
+# Generated by Django 6.0.6 on 2026-06-18 21:03
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+def backfill_related_game(apps, schema_editor):
+    """Move each add-on purchase's parent link from the parent *purchase* to a
+    parent *game*. For a parent bought as a multi-game bundle there is no single
+    game, so use the bundle's first game (by sort_name) as the best guess."""
+    Purchase = apps.get_model("games", "Purchase")
+    for purchase in Purchase.objects.filter(related_purchase__isnull=False):
+        parent_game = purchase.related_purchase.games.order_by("sort_name").first()
+        if parent_game is not None:
+            purchase.related_game = parent_game
+            purchase.save(update_fields=["related_game"])
+
+
+def noop_reverse(apps, schema_editor):
+    pass
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("games", "0019_alter_filterpreset_mode"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="purchase",
+            name="related_game",
+            field=models.ForeignKey(
+                blank=True,
+                default=None,
+                null=True,
+                on_delete=django.db.models.deletion.SET_NULL,
+                related_name="addon_purchases",
+                to="games.game",
+            ),
+        ),
+        migrations.RunPython(backfill_related_game, noop_reverse),
+        migrations.RemoveField(
+            model_name="purchase",
+            name="related_purchase",
+        ),
+    ]

games/models.py

@@ -198,12 +198,13 @@ class Purchase(models.Model):
     )
     type = models.CharField(max_length=255, choices=TYPES, default=GAME)
     name = models.CharField(max_length=255, blank=True, default="")
-    related_purchase = models.ForeignKey(
-        "self",
+    related_game = models.ForeignKey(
+        Game,
         on_delete=models.SET_NULL,
         default=None,
         null=True,
-        related_name="related_purchases",
+        blank=True,
+        related_name="addon_purchases",
     )
     created_at = models.DateTimeField(auto_now_add=True)
     updated_at = models.DateTimeField(auto_now=True)
@@ -252,9 +253,9 @@ class Purchase(models.Model):
         self.save()
 
     def save(self, *args, **kwargs):
-        if self.type != Purchase.GAME and not self.related_purchase:
+        if self.type != Purchase.GAME and not self.related_game:
             raise ValidationError(
-                f"{self.get_type_display()} must have a related purchase."
+                f"{self.get_type_display()} must have a related game."
             )
         super().save(*args, **kwargs)
 

games/static/js/add_purchase.js

@@ -1,40 +1,23 @@
 import { getEl, disableElementsWhenTrue, onSwap } from "./utils.js";
 
-const RELATED_PURCHASE_URL = "/tracker/purchase/related-purchase-by-game";
-
 // The games field is now a SearchSelect widget (a <div>, not a <select>), so we
 // react to its custom "search-select:change" event instead of syncing a select.
 document.addEventListener("search-select:change", (event) => {
   if (event.detail.name !== "games") return;
 
-  // (a) Auto-fill platform from the clicked option's data-platform.
+  // Auto-fill platform from the clicked option's data-platform.
   const last = event.detail.last;
   const platformId = last && last.data ? last.data.platform : "";
   if (platformId) {
     const platformEl = getEl("#id_platform");
     if (platformEl) platformEl.value = platformId;
   }
-
-  // (b) Refresh #id_related_purchase for the currently selected games.
-  const query = event.detail.values
-    .map((value) => "games=" + encodeURIComponent(value))
-    .join("&");
-  fetch(RELATED_PURCHASE_URL + "?" + query, { credentials: "same-origin" })
-    .then((response) => {
-      if (response.status === 204) return null;
-      return response.text();
-    })
-    .then((html) => {
-      if (html === null) return;
-      const target = getEl("#id_related_purchase");
-      if (target) target.outerHTML = html;
-    });
 });
 
 function setupElementHandlers() {
   disableElementsWhenTrue("#id_type", "game", [
     "#id_name",
-    "#id_related_purchase",
+    "#id_related_game",
   ]);
 }
 

games/urls.py

@@ -105,11 +105,6 @@ urlpatterns = [
         purchase.refund_purchase,
         name="refund_purchase",
     ),
-    path(
-        "purchase/related-purchase-by-game",
-        purchase.related_purchase_by_game,
-        name="related_purchase_by_game",
-    ),
     path("session/add", session.add_session, name="add_session"),
     path(
         "session/add/for-game/<int:game_id>",

games/views/purchase.py

@@ -393,25 +393,3 @@ def finish_purchase(request: HttpRequest, purchase_id: int) -> HttpResponse:
         game.status = Game.Status.FINISHED
         game.save()
     return redirect("games:list_purchases")
-
-
-def related_purchase_by_game(request: HttpRequest) -> HttpResponse:
-    games: list[str] = request.GET.getlist("games")
-    if games:
-        from games.forms import related_purchase_queryset
-
-        form = PurchaseForm()
-        qs = (
-            related_purchase_queryset()
-            .filter(games__in=games)
-            .order_by("games__sort_name")
-        )
-
-        form.fields["related_purchase"].queryset = qs
-        first_option = qs.first()
-        if first_option:
-            form.fields["related_purchase"].initial = first_option.id
-        return HttpResponse(str(form["related_purchase"]))
-    else:
-        # abort swap
-        return HttpResponse(status=204)