Optimize DREF3 pagination by appeal_code

dref/test_dref3_filters.py

@@ -1,6 +1,7 @@
 from datetime import datetime, timedelta
 
 from django.contrib.auth import get_user_model
+from django.utils import timezone
 from rest_framework import status
 
 from api.models import Country, Region, RegionName
@@ -145,14 +146,46 @@ def test_pagination(self):
         self.authenticate(self.superuser)
         full = self.client.get(self.url)
         self.assertEqual(full.status_code, status.HTTP_200_OK)
-        total = len(full.json())
+        all_rows = full.json()
+        total_codes = {row["appeal_id"] for row in all_rows}
         page1 = self.client.get(self.url, {"limit": 1, "offset": 0})
         self.assertEqual(page1.status_code, status.HTTP_200_OK)
-        assert len(page1.json()) == 1
-        if total > 1:
+        page1_rows = page1.json()
+        assert len({row["appeal_id"] for row in page1_rows}) == 1
+        if len(total_codes) > 1:
             page2 = self.client.get(self.url, {"limit": 1, "offset": 1})
             self.assertEqual(page2.status_code, status.HTTP_200_OK)
-            assert len(page2.json()) == 1
+            page2_rows = page2.json()
+            assert len({row["appeal_id"] for row in page2_rows}) == 1
+            assert {row["appeal_id"] for row in page2_rows} != {row["appeal_id"] for row in page1_rows}
+
+    def test_pagination_order_by_created_at(self):
+        self.authenticate(self.superuser)
+        now = timezone.now()
+        self.dref_a.created_at = now - timedelta(days=2)
+        self.dref_a.save(update_fields=["created_at"])
+        self.dref_b.created_at = now - timedelta(days=1)
+        self.dref_b.save(update_fields=["created_at"])
+
+        page1 = self.client.get(self.url, {"limit": 1, "offset": 0, "order_by": "created_at"})
+        self.assertEqual(page1.status_code, status.HTTP_200_OK)
+        page1_codes = {row["appeal_id"] for row in page1.json()}
+        assert page1_codes == {"APPEAL_A"}
+
+        page2 = self.client.get(self.url, {"limit": 1, "offset": 1, "order_by": "created_at"})
+        self.assertEqual(page2.status_code, status.HTTP_200_OK)
+        page2_codes = {row["appeal_id"] for row in page2.json()}
+        assert page2_codes == {"APPEAL_B"}
+
+        page1_desc = self.client.get(self.url, {"limit": 1, "offset": 0, "order_by": "-created_at"})
+        self.assertEqual(page1_desc.status_code, status.HTTP_200_OK)
+        page1_desc_codes = {row["appeal_id"] for row in page1_desc.json()}
+        assert page1_desc_codes == {"APPEAL_B"}
+
+        page2_desc = self.client.get(self.url, {"limit": 1, "offset": 1, "order_by": "-created_at"})
+        self.assertEqual(page2_desc.status_code, status.HTTP_200_OK)
+        page2_desc_codes = {row["appeal_id"] for row in page2_desc.json()}
+        assert page2_desc_codes == {"APPEAL_A"}
 
     def test_export_csv(self):
         self.authenticate(self.superuser)

dref/views.py

@@ -8,7 +8,7 @@
 from django.http import HttpResponse
 from django.templatetags.static import static
 from django.utils.translation import gettext
-from drf_spectacular.utils import extend_schema
+from drf_spectacular.utils import OpenApiParameter, extend_schema
 from rest_framework import (
     mixins,
     permissions,
@@ -464,6 +464,52 @@ def _status_to_int(self, raw):
         name_map = {s.name.lower(): s.value for s in Dref.Status}
         return label_map.get(str(raw).lower()) or name_map.get(str(raw).lower())
 
+    def _order_codes(self, codes, request):
+        order_by = request.query_params.get("order_by")
+        if order_by not in ("created_at", "-created_at"):
+            return sorted(codes)
+
+        created_map = {
+            row["appeal_code"]: row["first_created_at"]
+            for row in Dref.objects.filter(appeal_code__in=codes)
+            .values("appeal_code")
+            .annotate(first_created_at=models.Min("created_at"))
+        }
+
+        present = [code for code in codes if created_map.get(code) is not None]
+        missing = sorted([code for code in codes if created_map.get(code) is None])
+        present_sorted = sorted(present, key=lambda code: (created_map.get(code), code), reverse=order_by == "-created_at")
+        return present_sorted + missing
+
+    def _paginate_codes(self, codes, request):
+        try:
+            limit = int(request.query_params.get("limit")) if request.query_params.get("limit") else None
+        except ValueError:
+            limit = None
+        try:
+            offset = int(request.query_params.get("offset")) if request.query_params.get("offset") else 0
+        except ValueError:
+            offset = 0
+
+        if not offset and limit is None:
+            return codes
+
+        end = offset + limit if limit is not None else None
+        return codes[offset:end]
+
+    @extend_schema(
+        parameters=[
+            OpenApiParameter(
+                name="order_by",
+                description=(
+                    "Ordering for paged appeal codes. Use 'created_at' or '-created_at' to sort by the first "
+                    "DREF application created_at per appeal_code; any other value defaults to appeal_code ordering."
+                ),
+                required=False,
+                type=str,
+            )
+        ]
+    )
     def list(self, request):
         # === First approach – would be nice to work like this, but recent definitons are more complex than that:
         # # Aggregate all appeal-codes from the three models
@@ -564,7 +610,7 @@ def list(self, request):
             combined = set()
             for s in codes_sets:
                 combined.update([c for c in s if c])
-            codes = sorted(combined)
+            codes = list(combined)
 
         # Additional date range filters (applied to root Dref only where fields exist)
         date_range_fields = [
@@ -592,6 +638,9 @@ def list(self, request):
             if excluded_codes:
                 codes = [c for c in codes if c and c.upper() not in excluded_codes]
 
+        codes = self._order_codes(codes, request)
+        codes = self._paginate_codes(codes, request)
+
         data = []
         old_kwargs = getattr(self, "kwargs", {}).copy()
         self.kwargs = {self.lookup_field: codes}
@@ -630,20 +679,7 @@ def list(self, request):
         if id_param:
             if wanted_ids := {i.strip() for i in str(id_param).split(",")}:
                 data = [row for row in data if row.get("id") in wanted_ids]
-        # pagination
-        try:
-            limit = int(request.query_params.get("limit")) if request.query_params.get("limit") else None
-        except ValueError:
-            limit = None
-        try:
-            offset = int(request.query_params.get("offset")) if request.query_params.get("offset") else 0
-        except ValueError:
-            offset = 0
-        if offset or limit is not None:
-            end = offset + limit if limit is not None else None
-            data_paginated = data[offset:end]
-        else:
-            data_paginated = data
+        data_paginated = data
 
         export_param = request.query_params.get("export")
         if export_param and export_param.lower() == "csv":