[12.x] Add withRelationshipAutoloading method to model (#55344)

* Add withRelationshipAutoloading method to model

* Update HasRelationships.php

---------

Co-authored-by: Taylor Otwell <taylor@laravel.com>

Author: litvinchuk

src/Illuminate/Database/Eloquent/Concerns/HasRelationships.php

@@ -1117,6 +1117,18 @@ public function setRelations(array $relations)
         return $this;
     }
 
+    /**
+     * Enable relationship autoloading for this model.
+     *
+     * @return $this
+     */
+    public function withRelationshipAutoloading()
+    {
+        $this->newCollection([$this])->withRelationshipAutoloading();
+
+        return $this;
+    }
+
     /**
      * Duplicate the instance and unset all the loaded relations.
      *

tests/Integration/Database/EloquentModelRelationAutoloadTest.php

@@ -32,7 +32,7 @@ protected function afterRefreshingDatabase()
         });
     }
 
-    public function testRelationAutoload()
+    public function testRelationAutoloadForCollection()
     {
         $post1 = Post::create();
         $comment1 = $post1->comments()->create(['parent_id' => null]);
@@ -63,6 +63,29 @@ public function testRelationAutoload()
         $this->assertTrue($posts[0]->comments[0]->relationLoaded('likes'));
     }
 
+    public function testRelationAutoloadForSingleModel()
+    {
+        $post = Post::create();
+        $comment1 = $post->comments()->create(['parent_id' => null]);
+        $comment2 = $post->comments()->create(['parent_id' => $comment1->id]);
+        $comment2->likes()->create();
+        $comment2->likes()->create();
+
+        DB::enableQueryLog();
+
+        $likes = [];
+
+        $post->withRelationshipAutoloading();
+
+        foreach ($post->comments as $comment) {
+            $likes = array_merge($likes, $comment->likes->all());
+        }
+
+        $this->assertCount(2, DB::getQueryLog());
+        $this->assertCount(2, $likes);
+        $this->assertTrue($post->comments[0]->relationLoaded('likes'));
+    }
+
     public function testRelationAutoloadVariousNestedMorphRelations()
     {
         tap(Post::create(), function ($post) {