Using Model Factory States To Create Related Models

Laravel’s model factories can be used to automatically create related models when the factory is called. This is a great way to DRY up the arrange portion of your tests. Consider the following factory definition:

$factory->define(Comment::class, function ($faker) {
	return [
		'post_id' => factory(Post::class)->lazy(),
		'content' => $faker->sentence()
	];
});

This factory will create a Comment along with a Post whenever it is called unless the Post is explicitly provided.

// creates a Comment and a Post
factory(Comment::class)->create();

// uses the provided Post instead of creating one
$post = factory(Post::class)->create();
$comment = factory(Comment::class)->create([
	'post_id' => $post->id
]);

While the first example can save you from having to repeat the Post creation call across your test suite, I think it suffers from two problems. First, when a Comment is created with $comment = factory(Comment::class)->create(); I cannot tell just by looking at the test that a Post has also been created. This implicit behavior could confuse my future self or anyone else working with the code. Second, I will no longer be able to use the factory as an argument to the save() method:

$post->comments()->save(factory(Comment::class)->make());

This code will correctly assign the comment to the post, as expected. However, since the post_id is not explicitly provided to the comment factory an additional unassigned Post will be created.

Despite its convenience I think these two problems limit the usefulness of the lazy() method. Fortunately Laravel gives us a solution - model factory states:

$factory->define(Comment::class, function ($faker) {
	return [
		'content' => $faker->sentence()
	];
});

$factory->state(Comment::class, 'withPost', function ($faker) {
    return [
		'post_id' => factory(Post::class)->lazy(),
	];
});

By defining a state we can use the base Comment factory as an argument to the save() method without an additional Post being created. When we need a Comment with a Post we can be explicit and use the withPost state.

// No unassigned post since the base Comment factory does not define it
$post->comments()->save(factory(Comment::class)->make());

// Creates the Post but is explicit about it
$comment = factory(Comment::class)->states(['withPost'])->create();