[bug] Build line fix (#12892)

* Fix BuildLineSerializer

- use SubquerySum not Sum

* Add regression test

* Adjust existing API test thresholds

* Refactor assertion message in test_api.py

Simplified assertion message for GROUP BY check in count queries.

* Fix assertion message in count query test

src/backend/InvenTree/build/serializers.py

@@ -13,7 +13,6 @@ from django.db.models import (
     F,
     FloatField,
     Q,
-    Sum,
     Value,
     When,
 )
@@ -22,6 +21,7 @@ from django.utils.translation import gettext_lazy as _
 
 from rest_framework import serializers
 from rest_framework.serializers import ValidationError
+from sql_util.utils import SubquerySum
 
 import common.filters
 import company.serializers
@@ -1574,7 +1574,9 @@ class BuildLineSerializer(
         # Annotate the "allocated" quantity
         queryset = queryset.annotate(
             allocated=Coalesce(
-                Sum('allocations__quantity'), 0, output_field=models.DecimalField()
+                SubquerySum('allocations__quantity'),
+                0,
+                output_field=models.DecimalField(),
             )
         )
 

src/backend/InvenTree/build/test_api.py

@@ -3,7 +3,9 @@
 from datetime import datetime, timedelta
 from typing import Optional
 
+from django.db import connection
 from django.db.models import Sum
+from django.test.utils import CaptureQueriesContext
 from django.urls import reverse
 
 from django_q.models import OrmQ
@@ -1858,14 +1860,11 @@ class BuildLineTests(BuildAPITest):
         self.assertEqual(len(response.data), BuildLine.objects.count())
 
         # Filter by 'available' status
-        # Note: The max_query_time is bumped up here, as postgresql backend has some strange issues (only during testing)
+        response = self.get(url, data={'available': True}, max_query_time=10)
-        # TODO: This needs to be addressed in the future, as 25 seconds is an unacceptably long time for a query to take in testing
-        response = self.get(url, data={'available': True}, max_query_time=25)
         n_t = len(response.data)
         self.assertGreater(n_t, 0)
 
-        # Note: The max_query_time is bumped up here, as postgresql backend has some strange issues (only during testing)
+        response = self.get(url, data={'available': False}, max_query_time=10)
-        response = self.get(url, data={'available': False}, max_query_time=25)
         n_f = len(response.data)
         self.assertGreater(n_f, 0)
 
@@ -2189,24 +2188,81 @@ class BuildLineTests(BuildAPITest):
         for line in lines:
             StockItem.objects.create(part=line.bom_item.sub_part, quantity=60)
 
-        # TODO: 2025-10-02: Work out why this query takes so long with PostgreSQL (in CI)
-        # Note: The max_query_time is bumped up here, as postgresql backend has some strange issues (only during testing)
         response = self.get(
-            url, {'build': build.pk, 'available': True}, max_query_time=30
+            url, {'build': build.pk, 'available': True}, max_query_time=10
         )
 
         # We expect 2 lines to have "available" stock
         self.assertEqual(len(response.data), 2)
 
-        # TODO: 2025-10-02: Work out why this query takes so long with PostgreSQL (in CI)
-        # Note: The max_query_time is bumped up here, as postgresql backend has some strange issues (only during testing)
         response = self.get(
-            url, {'build': build.pk, 'available': False}, max_query_time=30
+            url, {'build': build.pk, 'available': False}, max_query_time=10
         )
 
         self.assertEqual(len(response.data), 1)
         self.assertEqual(response.data[0]['pk'], lines[0].pk)
 
+    def test_list_unfiltered_count_query_has_no_group_by(self):
+        """Regression test for a bug where the (unfiltered) BuildLine list endpoint was catastrophically slow.
+
+        The specific trigger: a plain GET against the list endpoint with no 'build'
+        filter (BuildLineMixin.get_source_build() then returns None, so
+        BuildLineSerializer.annotate_queryset() runs across *every* BuildLine in the
+        database, unscoped) - e.g. an external API client just paging through results.
+        """
+        # Build line with a genuine stock allocation, to also confirm the 'allocated'
+        # value itself is still computed correctly after the Sum -> SubquerySum swap.
+        assembly = Part.objects.create(
+            name='Regression Test Assembly',
+            description='Assembly for BuildLine count() regression test',
+            assembly=True,
+        )
+        component = Part.objects.create(
+            name='Regression Test Component',
+            description='Component for BuildLine count() regression test',
+            component=True,
+        )
+        BomItem.objects.create(part=assembly, sub_part=component, quantity=1)
+
+        build = Build.objects.create(
+            part=assembly,
+            reference='BO-9996',
+            quantity=1,
+            title='BuildLine count() regression build',
+        )
+
+        line = build.build_lines.first()
+        stock_item = StockItem.objects.create(part=component, quantity=10)
+        BuildItem.objects.create(build_line=line, stock_item=stock_item, quantity=1)
+
+        url = reverse('api-build-line-list')
+
+        # Deliberately *no* 'build' filter - see docstring above
+        with CaptureQueriesContext(connection) as ctx:
+            response = self.get(url, {'limit': 1}, expected_code=200)
+
+        self.assertEqual(response.data['count'], BuildLine.objects.count())
+
+        count_queries = [
+            q
+            for q in ctx.captured_queries
+            if 'build_buildline' in q['sql'].lower()
+            and 'select count(' in q['sql'].lower()
+        ]
+        self.assertTrue(count_queries, 'Expected a COUNT query for list pagination')
+
+        for query in count_queries:
+            self.assertNotIn(
+                'GROUP BY',
+                query['sql'].upper(),
+                'BuildLine count() query should not require a GROUP BY',
+            )
+
+        # Confirm the 'allocated' value is still computed correctly
+        response = self.get(url, {'build': build.pk}, expected_code=200)
+        line_data = next(item for item in response.data if item['pk'] == line.pk)
+        self.assertEqual(line_data['allocated'], 1)
+
 
 class BuildConsumeTest(BuildAPITest):
     """Test consuming allocated stock."""