Yii2 - update record with child records - yii2

Question

I have a form which allows the user to add many child records, in my case they are called "Items". When updating the master record, the user can add, edit or delete child records. Everything works fine, but I am looking for a better way to do this.
Currently, in my Update action, I first delete any existing child records. I then save all the child records from the form post.
public function actionUpdate($id)
{
$model = $this->findModel($id);
if ($model->load(Yii::$app->request->post()) && $model->save()) {
// first delete all existing child records
Item::deleteAll(['parent_id' => $model->id]);
// get the new set of posted Items
$items = Yii::$app->request->post('Item');
if (!empty($items) && is_array($items)) {
// save each Item
foreach ($items as $index => $values) {
$item = new Item();
$item->attributes = $values;
$item->parent_id = $model->id;
$item->save();
}
}
return $this->redirect(['view', 'id' => $model->id]);
}
return $this->render('update', [
'model' => $model,
]);
}
Form View:
<form method="post" action="">
<?php foreach ($model->items as $index => $item): ?>
<?php echo Html::activeTextInput($item, "[$index]name"); ?>
<!-- Example output -->
<!-- <input id="item-0-name" name="Item[0][name]" value="Test" type="text"> -->
Remove this Item
<?php endforeach; ?>
<button type="submit">Submit</button>
</form>
Add a new Item
In the above $model->items refers to the relation in the parent model:
public function getItems()
{
return $this->hasMany(Item::className(), ['parent_id' => 'id']);
}
When the user clicks "Add a new Item" it simply uses JavaScript to clone the last item and replaces its index with the next value.
Very often, the user does not change any child records. So the process of deleting and re-adding child records in that case is pointless.
What I want to know is, is there a way I can intelligently handle this? For example:
Only delete child records if they do not exist in the POSTed Item array
Only edit the child records if they are different to the ones in the database
Only add new child records that do not currently exist in the database
Otherwise leave everything as it is

Answer 1

You can use indexBy() to define your relation to index related items by their ID:
public function getItems() {
return $this->hasMany(Item::class, [/*...*/])->indexBy('id');
}
Then you can check if record with this ID already exist and do update/delete/create action:
// get the new set of posted Items
$items = Yii::$app->request->post('Item');
$existing = $model->items;
if (!empty($items) && is_array($items)) {
// save each Item
foreach ($items as $index => $values) {
if (!isset($existing[$index])) {
// create new item
$item = new Item();
$item->attributes = $values;
$item->parent_id = $model->id;
$item->save();
} else {
// update existing
$existing[$index]->attributes = $values;
$existing[$index]->save();
// remove from $existing array as already processed
unset($existing[$index]);
}
}
// right now $existing has only existing and not updated items - it means
// that they're not available in POST data so we should remove it
foreach ($existing as $item) {
$item->delete();
}
}