core/core/metrics.py

@@ -0,0 +1,35 @@
+from django.apps import apps
+from prometheus_client.core import CounterMetricFamily, REGISTRY
+from django.db.models import Case, Value, When, BooleanField, Count
+from inventory.models import Item
+
+class ItemCountCollector(object):
+
+    def collect(self):
+        counter = CounterMetricFamily("item_count", "Current number of items", labels=['event', 'state'])
+
+        yield counter
+
+        if not apps.models_ready or not apps.apps_ready:
+            return
+
+        queryset = (
+            Item.all_objects
+                .annotate(
+                    returned=Case(
+                        When(returned_at__isnull=False, then=Value(False)),
+                        default=Value(True),
+                        output_field=BooleanField()
+                    )
+                )
+                .values('event__slug', 'returned', 'event_id')
+                .annotate(amount=Count('id'))
+                .order_by('event__slug', 'returned')  # Optional: order by slug and returned
+        )
+
+        for e in queryset:
+            counter.add_metric([e["event__slug"].lower(), str(e["returned"])], e["amount"])
+
+        yield counter
+
+REGISTRY.register(ItemCountCollector())

core/core/urls.py

@@ -19,6 +19,8 @@ from django.urls import path, include
 
 from .version import get_info
 
+from .metrics import *
+
 urlpatterns = [
     path('djangoadmin/', admin.site.urls),
     path('api/2/', include('inventory.api_v2')),