[9.x] Allow factories to recycle models with for method (#44265)

* Recycle models when using `for`

* formatting

* Add test for expected recycle behaviour

* Update BelongsToRelationship.php

Co-authored-by: Taylor Otwell <[email protected]>

Author: jessarcher

src/Illuminate/Database/Eloquent/Factories/BelongsToRelationship.php

@@ -69,7 +69,9 @@ protected function resolver($key)
     {
         return function () use ($key) {
             if (! $this->resolved) {
-                $instance = $this->factory instanceof Factory ? $this->factory->create() : $this->factory;
+                $instance = $this->factory instanceof Factory
+                    ? ($this->factory->recycle->get($this->factory->modelName()) ?? $this->factory->create())
+                    : $this->factory;
 
                 return $this->resolved = $key ? $instance->{$key} : $instance->getKey();
             }

src/Illuminate/Database/Eloquent/Factories/Factory.php

@@ -68,7 +68,7 @@ abstract class Factory
      *
      * @var \Illuminate\Support\Collection
      */
-    protected $recycle;
+    public $recycle;
 
     /**
      * The "after making" callbacks that will be applied to the model.

tests/Database/DatabaseEloquentFactoryTest.php

@@ -670,6 +670,37 @@ public function test_model_instances_can_be_used_in_place_of_nested_factories()
         $this->assertEquals($user->id, $post->comments[1]->user_id);
     }
 
+    public function test_for_method_recycles_models()
+    {
+        Factory::guessFactoryNamesUsing(function ($model) {
+            return $model.'Factory';
+        });
+
+        $user = FactoryTestUserFactory::new()->create();
+        $post = FactoryTestPostFactory::new()
+            ->recycle($user)
+            ->for(FactoryTestUserFactory::new())
+            ->create();
+
+        $this->assertSame(1, FactoryTestUser::count());
+    }
+
+    public function test_has_method_does_not_reassign_the_parent()
+    {
+        Factory::guessFactoryNamesUsing(function ($model) {
+            return $model.'Factory';
+        });
+
+        $post = FactoryTestPostFactory::new()->create();
+        $user = FactoryTestUserFactory::new()
+            ->recycle($post)
+            // The recycled post already belongs to a user, so it shouldn't be recycled here.
+            ->has(FactoryTestPostFactory::new(), 'posts')
+            ->create();
+
+        $this->assertSame(2, FactoryTestPost::count());
+    }
+
     /**
      * Get a database connection instance.
      *