From e125ad559b3925248e541950a881dfe8a13af58c Mon Sep 17 00:00:00 2001
From: Indra Gunawan <hello@indra.my.id>
Date: Wed, 1 Oct 2025 18:15:34 +0800
Subject: [PATCH] support default value for new collection item

---
 src/LiveComponent/src/LiveCollectionTrait.php |  7 ++++-
 .../tests/Unit/LiveCollectionTraitTest.php    | 28 +++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/src/LiveComponent/src/LiveCollectionTrait.php b/src/LiveComponent/src/LiveCollectionTrait.php
index 70f11f23b8b..e31b98e061d 100644
--- a/src/LiveComponent/src/LiveCollectionTrait.php
+++ b/src/LiveComponent/src/LiveCollectionTrait.php
@@ -34,7 +34,7 @@ public function addCollectionItem(PropertyAccessorInterface $propertyAccessor, #
         }
 
         $index = [] !== $data ? max(array_keys($data)) + 1 : 0;
-        $propertyAccessor->setValue($this->formValues, $propertyPath."[$index]", []);
+        $propertyAccessor->setValue($this->formValues, $propertyPath."[$index]", $this->setCollectionItemDefaultValue($propertyPath, $index));
     }
 
     #[LiveAction]
@@ -60,4 +60,9 @@ private function fieldNameToPropertyPath(string $collectionFieldName, string $ro
 
         return $propertyPath;
     }
+
+    protected function setCollectionItemDefaultValue(string $propertyPath, int $index): iterable
+    {
+        return [];
+    }
 }
diff --git a/src/LiveComponent/tests/Unit/LiveCollectionTraitTest.php b/src/LiveComponent/tests/Unit/LiveCollectionTraitTest.php
index 12e92730e77..2c7876984f1 100644
--- a/src/LiveComponent/tests/Unit/LiveCollectionTraitTest.php
+++ b/src/LiveComponent/tests/Unit/LiveCollectionTraitTest.php
@@ -73,6 +73,23 @@ public static function provideAddedItems(): iterable
                 ],
             ],
         ];
+        yield 'named parent, default value' => [
+            [
+                'parentName' => [
+                    'collectionNameDefault' => null,
+                ],
+            ],
+            'parentName[collectionNameDefault]',
+            [
+                'parentName' => [
+                    'collectionNameDefault' => [
+                        0 => [
+                            'property' => 'value',
+                        ],
+                    ],
+                ],
+            ],
+        ];
         yield 'named parent, empty array value' => [
             [
                 'parentName' => [
@@ -221,6 +238,17 @@ protected function instantiateForm(): FormInterface
             {
                 return $this->theForm;
             }
+
+            protected function setCollectionItemDefaultValue(string $propertyPath, int $index): iterable
+            {
+                if ('[collectionNameDefault]' === $propertyPath) {
+                    return [
+                        'property' => 'value',
+                    ];
+                }
+
+                return [];
+            }
         };
         $component->formName = array_key_first($postedFormData);
         $component->formValues = $postedFormData[$component->formName];