Unset _id: null to let it be autogenerated

CHANGELOG.md

@@ -4,6 +4,7 @@ All notable changes to this project will be documented in this file.
 ## [4.4.0] - unreleased
 
 * Support collection name prefix by @GromNaN in [#2930](https://github.com/mongodb/laravel-mongodb/pull/2930)
+* Ignore `_id: null` to let MongoDB generate an `ObjectId` by @GromNaN in [#2969](https://github.com/mongodb/laravel-mongodb/pull/2969)
 * Add `mongodb` driver for Batching by @GromNaN in [#2904](https://github.com/mongodb/laravel-mongodb/pull/2904)
 * Rename queue option `table` to `collection`
 * Replace queue option `expire` with `retry_after`

src/Eloquent/Builder.php

@@ -21,6 +21,7 @@
 use function collect;
 use function is_array;
 use function iterator_to_array;
+use function json_encode;
 
 /** @method \MongoDB\Laravel\Query\Builder toBase() */
 class Builder extends EloquentBuilder
@@ -210,8 +211,8 @@ public function raw($value = null)
      */
     public function createOrFirst(array $attributes = [], array $values = []): Model
     {
-        if ($attributes === []) {
-            throw new InvalidArgumentException('You must provide attributes to check for duplicates');
+        if ($attributes === [] || $attributes === ['_id' => null]) {
+            throw new InvalidArgumentException('You must provide attributes to check for duplicates. Got ' . json_encode($attributes));
         }
 
         // Apply casting and default values to the attributes

src/Eloquent/Model.php

@@ -746,6 +746,12 @@ protected function isBSON(mixed $value): bool
      */
     public function save(array $options = [])
     {
+        // SQL databases would use autoincrement the id field if set to null.
+        // Apply the same behavior to MongoDB with _id only, otherwise null would be stored.
+        if (array_key_exists('_id', $this->attributes) && $this->attributes['_id'] === null) {
+            unset($this->attributes['_id']);
+        }
+
         $saved = parent::save($options);
 
         // Clear list of unset fields

tests/ModelTest.php

@@ -1151,4 +1151,21 @@ public function testUpdateOrCreate(array $criteria)
         $this->assertEquals($createdAt, $checkUser->created_at->getTimestamp());
         $this->assertEquals($updatedAt, $checkUser->updated_at->getTimestamp());
     }
+
+    public function testCreateWithNullId()
+    {
+        $user = User::create(['_id' => null, 'email' => 'foo@bar']);
+        $this->assertNotNull(ObjectId::class, $user->id);
+        $this->assertSame(1, User::count());
+    }
+
+    public function testUpdateOrCreateWithNullId()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('You must provide attributes to check for duplicates');
+        User::updateOrCreate(
+            ['_id' => null],
+            ['email' => 'jane.doe@example.com'],
+        );
+    }
 }