[6.x] Resolve Entry::descendants() N+1 query

src/Entries/Entry.php

@@ -869,8 +869,26 @@ public function descendants()
     {
         $localizations = $this->directDescendants();
 
-        foreach ($localizations as $loc) {
-            $localizations = $localizations->merge($loc->descendants());
+        // Breadth-first: fetch each level in one batched query instead of one query per node.
+        $origins = $localizations->map->id()->values()->all();
+        $seen = array_merge($origins, [$this->id()]);
+
+        while (! empty($origins)) {
+            $children = Facades\Entry::query()
+                ->where('collection', $this->collectionHandle())
+                ->whereIn('origin', $origins)
+                ->get()
+                // Guard against cyclic or duplicate origin data, which would
+                // otherwise loop forever as the same entries reappear.
+                ->reject(fn ($entry) => in_array($entry->id(), $seen, true));
+
+            if ($children->isEmpty()) {
+                break;
+            }
+
+            $localizations = $localizations->merge($children->keyBy->locale());
+            $origins = $children->map->id()->values()->all();
+            $seen = array_merge($seen, $origins);
         }
 
         return $localizations;

tests/Data/Entries/EntryTest.php

@@ -1577,6 +1577,74 @@ public function it_propagates_entry_if_configured()
         });
     }
 
+    #[Test]
+    public function it_resolves_descendants_with_one_query_per_level_rather_than_one_per_localization()
+    {
+        $collection = (new Collection)->handle('pages')->save();
+
+        $entry = (new Entry)->id('a')->locale('en')->collection($collection);
+
+        // Three direct localizations, all leaves (no further descendants).
+        $fr = (new Entry)->id('b')->locale('fr')->origin('a')->collection($collection);
+        $de = (new Entry)->id('c')->locale('de')->origin('a')->collection($collection);
+        $es = (new Entry)->id('d')->locale('es')->origin('a')->collection($collection);
+
+        // A flat tree is one level deep, so it should take exactly two queries
+        // (the direct descendants, then a single batched lookup for the next
+        // level which comes back empty) regardless of how many localizations
+        // exist. The previous recursive implementation issued one query per
+        // node, i.e. O(number of localizations).
+        Facades\Entry::shouldReceive('query')->times(2)->andReturn(
+            $this->fakeDescendantsQuery(collect([$fr, $de, $es])),       // direct descendants of 'a'
+            $this->fakeDescendantsQuery(collect(), ['b', 'c', 'd']),     // batched lookup for the next level
+        );
+
+        $descendants = $entry->descendants();
+
+        $this->assertEquals(['de', 'es', 'fr'], $descendants->keys()->sort()->values()->all());
+    }
+
+    #[Test]
+    public function it_includes_descendants_nested_via_an_origin_chain()
+    {
+        $collection = (new Collection)->handle('pages')->save();
+
+        $entry = (new Entry)->id('a')->locale('en')->collection($collection);
+
+        // de's origin is fr, whose origin is en: a grandchild only reachable by
+        // walking past the first level. The flattened result must include it.
+        $fr = (new Entry)->id('b')->locale('fr')->origin('a')->collection($collection);
+        $de = (new Entry)->id('c')->locale('de')->origin('b')->collection($collection);
+
+        Facades\Entry::shouldReceive('query')->times(3)->andReturn(
+            $this->fakeDescendantsQuery(collect([$fr])),         // direct descendants of en
+            $this->fakeDescendantsQuery(collect([$de]), ['b']),  // batched descendants of fr
+            $this->fakeDescendantsQuery(collect(), ['c']),       // batched descendants of de
+        );
+
+        $descendants = $entry->descendants();
+
+        $this->assertEquals(['de', 'fr'], $descendants->keys()->sort()->values()->all());
+        $this->assertSame($fr, $descendants->get('fr'));
+        $this->assertSame($de, $descendants->get('de'));
+    }
+
+    private function fakeDescendantsQuery($results, ?array $whereInOrigins = null): QueryBuilder
+    {
+        $query = Mockery::mock(QueryBuilder::class);
+        $query->shouldReceive('where')->with('collection', 'pages')->andReturnSelf();
+
+        if ($whereInOrigins === null) {
+            // directDescendants() uses where('origin', string); batched levels use whereIn.
+            $query->shouldReceive('where')->with('origin', Mockery::type('string'))->andReturnSelf();
+        }
+
+        $query->shouldReceive('whereIn')->with('origin', $whereInOrigins ?? Mockery::type('array'))->andReturnSelf();
+        $query->shouldReceive('get')->andReturn($results);
+
+        return $query;
+    }
+
     #[Test]
     public function it_doesnt_fire_events_when_propagating_entry_and_saved_quietly()
     {