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Avoid describing your data multiple times in a Laravel app using laravel-data

Original – by Ruben Van Assche – 12 minute read

In the vast majority of applications you work with data structures. Sometimes that data is described multiple times. Think for instance of a form request that tries to validate a blog post model, and an API transformer class for that same blog post model. Changes are that both classes describe the same properties.

Using our new laravel-data package, those structures only need to be described once.

Instead of form requests, you can use a data object. Instead of API transformers, you can use a data object. Instead of manually writing typescript definitions, you can use... 🥁 a data object

In this blog post, I'll guide you through the most important functionalities of the package and how to use them.

Getting started

First, you should install the package.

We're going to create a blog with different posts so let's get started with the PostData object. A post has a title, some content, a status and a date when it was published:

class PostData extends Data
{
    public function __construct(
        public string $title,
        public string $content,
        public PostStatus $status,
        public ?CarbonImmutable $published_at
    ) {
    }
}

The only requirement for using the package is extending your data objects from the base Data object. We add the requirements for a post as public properties.

The PostStatus is an enum using the spatie/enum package:

/**
 * @method static self draft()
 * @method static self published()
 * @method static self archived()
 */
class PostStatus extends Enum
{

}

We store this PostData object as app/Data/PostData.php, so we have all our data objects bundled in one directory. Of course, you're free to store them wherever you want within your application.

We can now create this a PostData object just like any plain PHP object:

$post = new PostData(
    'Hello laravel-data',
    'This is an introduction post for the new package',
    PostStatus::published(),
    CarbonImmutable::now()
);

The package also allows you to create these data objects from any type, for example, an array:

$post = PostData::from([
    'title' => 'Hello laravel-data',
    'content' => 'This is an introduction post for the new package',
    'status' => PostStatus::published(),
    'published_at' => CarbonImmutable::now(),
]);

Using requests and casts

Now let's say we have request with these properties. Our controller would then look like this:

public function __invoke(Request $request)
{
    $post = PostData::from([
        'title' => $request->input('title'),
        'content' => $request->input('content'),
        'status' => PostStatus::from($request->input('status')),
        'published_at' => CarbonImmutable::createFromFormat(DATE_ATOM, $request->input('published_at')),
    ]);
}

That's a lot of code just to fill a data object. It would be a lot nicer if we could do this:

public function __invoke(Request $request)
{
    $post = PostData::from($request);
}

But this throws the following exception:

TypeError: App\Data\PostData::__construct(): Argument #3 ($status) must be of type App\Enums\PostStatus, string given

That's because the status property expects a PostStatus enum object, but it gets a string. We can fix this by implementing a cast for enums:

class PostStatusCast implements Cast
{
    public function cast(DataProperty $property, mixed $value): PostStatus
    {
        return PostStatus::from($value);
    }
}

And tell the package always to use this cast when trying to create a PostData object:

class PostData extends Data
{
    public function __construct(
        public string $title,
        public string $content,
        #[WithCast(PostStatusCast::class)]
        public PostStatus $status,
        public ?CarbonImmutable $published_at
    ) {
    }
}

Using global casts

Let's send the following payload to the controller:

{
    "title" : "Hello laravel-data",
    "content" : "This is an introduction post for the new package",
    "status" : "published",
    "published_at" : "2021-09-24T13:31:20+00:00"
}

We get the PostData object populated with the values in the JSON payload, neat! But how did the package convert the published_at string into a CarbonImmutable object?

It is possible to define global casts within the data.php config file. These casts will be used on data objects if no other casts can be found.

By default, the global casts list looks like this:

'casts' => [
    DateTimeInterface::class => Spatie\LaravelData\Casts\DateTimeInterfaceCast::class,
],

This means that if a class property is of type DateTime, Carbon, CarbonImmutable, ... it will be automatically converted.

You can read more about casting here.

Validation using form requests

Since we're working with requests, wouldn't it be cool to validate the data coming in from the request using the data object? Typically, you would create a request with a validator like this:

class PostDataRequest extends FormRequest
{
    public function authorize()
    {
        return false;
    }

    public function rules()
    {
        return [
            'title' => ['required', 'string', 'max:200'],
            'content' => ['required', 'string'],
            'status' => ['required', 'string', 'in:draft,published,archived'],
            'published_at' => ['nullable', 'date']
        ];
    }
}

Thanks to PHP 8.0 attributes, we can completely omit this PostDataRequest and use the data object instead:

class PostData extends Data
{
    public function __construct(
        #[Required, StringType, Max(200)]
        public string $title,
        #[Required, StringType]
        public string $content,
        #[Required, StringType, In(['draft', 'published', 'archived'])]
        public PostStatus $status,
        #[Nullable, Date]
        public ?CarbonImmutable $published_at
    ) {
    }
}

You can now inject the data object into your application, just like a Laravel form request:

public function __invoke(PostData $data)
{
    dd($data); // a filled in data object
}

When the given data is invalid, a user will be redirected back with the validation errors in the error bag. If a validation occurs when making a JSON request, a 422 response will be returned with the validation errors.

Because our data object is so well-typed, we can even drop some validation rules since they can be automatically deduced:

class PostData extends Data
{
    public function __construct(
        #[Max(200)]
        public string $title,
        public string $content,
        #[StringType, In(['draft', 'published', 'archived'])]
        public PostStatus $status,
        #[Date]
        public ?CarbonImmutable $published_at
    ) {
    }
}

There's still much more you can do with validating data objects. Read more about it here.

Using a data object to get the request data from anywhere

Typically, you would use a controller to get the request data, and pass it to objects that need that data.

There's also another pragmatic way to get to the request data: you can resolve a data object from the container:

app(PostData::class);

The returned PostData instance will be filled with data from the request. If for some reason the request data could not be mapped upon the data object (maybe validation failed), than the package will throw a Illuminate\Validation\ValidationException.

In most cases, you won't need this, but it's cool that you can.

Working with Eloquent models

In our application, we have a Post Eloquent model:

class Post extends Model
{
    protected $fillable = '*';

    protected $casts = [
        'status' => PostStatus::class
    ];

    protected $dates = [
        'published_at'
    ];
}

Thanks to the casts we added earlier, this can be quickly transformed into a PostData object:

PostData::from(Post::findOrFail($id));

Customizing the creation of a data object

It is even possible to manually define how such a model is mapped onto a data object. To demonstrate that, we will take a completely different example that shows the strength of the from method.

What if we would like to support to create posts via an email syntax like this:

title|status|content

Creating a PostData object would then look like this:

PostData::from('Hello laravel-data|draft|This is an introduction post for the new package');

To make this work, we need to add a magic creation function within our data class:

class PostData extends Data
{
    public function __construct(
        public string $title,
        public string $content,
        #[WithCast(PostStatusCast::class)]
        public PostStatus $status,
        public ?CarbonImmutable $published_at
    ) {
    }
    
    public static function fromString(string $post): PostData
    {
        $fields = explode('|', $post);
    
        return new self(
            $fields[0],
            $fields[2],
            PostStatus::from($fields[1]),
            null
        );
    }
}

Magic creation methods allow you to create data objects from any type by passing them to the from method of a data object, you can read more about it here.

It can be convenient to transform more complex models than our Post into data objects because you can decide how a model would be mapped onto a data object.

Nesting data objects and collections

Now that we have a fully functional post data object. We're going to create a new data object, AuthorData that will store the name of an author and a collection of posts the author wrote:

class AuthorData extends Data
{
    public function __construct(
        public string $name,
        /** @var \App\Data\PostData[] */
        public DataCollection $posts
    ) {
    }
}

Instead of using an array to store all the posts, we use a DataCollection. This will be very useful later on! We now can create an author object as such:

new AuthorData(
    'Ruben Van Assche',
    PostData::collection([
        new PostData('Hello laravel-data', 'This is an introduction post for the new package', PostStatus::draft(), null),
        new PostData('What is a data object', 'How does it work?', PostStatus::draft(), null),
    ])
);

But it is also possible to create an author using the from method:

AuthorData::from([
    'name' => 'Ruben Van Assche',
    'posts' => [
        [
            'title' => 'Hello laravel-data',
            'content' => 'This is an introduction post for the new package',
            'status' => 'draft',
            'published_at' => null,
        ],
        [
            'title' => 'What is a data object',
            'content' => 'How does it work',
            'status' => 'draft',
            'published_at' => null,
        ],
    ],
]);

The data object is smart enough to convert an array of posts into a data collection of post data. Mapping data coming from the frontend was never that easy!

You can do a lot more with data collections. Read more about it here.

Usage in controllers

We've been creating many data objects from all sorts of values, time to change course and go the other way around and start transforming data objects into arrays.

Let's say we have an API controller that returns a post:

public function __invoke()
{
    return new PostData(
        'Hello laravel-data',
        'This is an introduction post for the new package',
        PostStatus::published(),
        CarbonImmutable::create(2020, 05, 16),
    );
}

By returning a data object in a controller, it is automatically converted to JSON:

{
    "title" : "Hello laravel-data",
    "content" : "This is an introduction post for the new package",
    "status" : "published",
    "published_at" : "2021-09-24T13:31:20+00:00"
}

You can also easily convert a data object into an array as such:

$postData->toArray();

Which gives you an array like this:

[
    'title' => 'Hello laravel-data',
    'content' => 'This is an introduction post for the new package',
    'status' => 'published',
    'published_at' => '2021-09-24T13:31:20+00:00',
]

It is possible to transform a data object into an array and keep complex types like the PostStatus and CarbonImmutable:

$postData->all();

This will give the following array:

[
    'title' => 'Hello laravel-data',
    'content' => 'This is an introduction post for the new package',
    'status' => PostStatus::published(),
    'published_at' => CarbonImmutable::create(2020, 05, 16),
]

As you can see, if we transform a data object to JSON, the CarbonImmutable published at date is transformed into a string.

Using transformers

A few sections ago, we used casts to convert simple types into complex types. Transformers work the other way around. They transform complex types into simple ones and transform a data object into a simpler structure like an array or JSON.

Just like the DateTimeInterfaceCast we also have a DateTimeInterfaceTransformer that will convert DateTime, Carbon, ... objects into strings.

This DateTimeInterfaceTransformer is registered in the data.php config file and will automatically be used when a data object needs to transform a DateTimeInterface object:

'transformers' => [
    DateTimeInterface::class => \Spatie\LaravelData\Transformers\DateTimeInterfaceTransformer::class,
    \Illuminate\Contracts\Support\Arrayable::class => \Spatie\LaravelData\Transformers\ArrayableTransformer::class,
],

The value of the PostStatus enum is automatically transformed to a string because it implements JsonSerializable, but it is perfectly possible to write a custom transformer for it just like we built our custom cast a few sections ago:

class PostStatusTransformer implements Transformer
{
    public function transform(DataProperty $property, mixed $value): string
    {
        /** @var \App\Enums\PostStatus $value */
        return $value->value;
    }
}

We now can use this transformer in the data object like this:

class PostData extends Data
{
    public function __construct(
        public string $title,
        public string $content,
        #[WithTransformer(PostStatusTransformer::class)]
        public PostStatus $status,
        public ?CarbonImmutable $published_at
    ) {
    }
}

You can read a lot more about transformers here.

Generating a blueprint

We now can send our posts as JSON to the front, but what if we want to create a new post? When using Inertia, for example, we might need an empty blueprint object like this that the user could fill in:

{
    "title" : null,
    "content" : null,
    "status" : null,
    "published_at" : null
}

This can be done with the empty method, which will return an empty array following the structure of your data object:

PostData::empty();

This will return the following array:

[
  'title' => null,
  'content' => null,
  'status' => null,
  'published_at' => null,
]

It is possible to set the status of the post to draft by default:

PostData::empty([
    'status' => 'draft';
]);

In closing

I hope you liked this quick overview of this package. There's still a lot more you can do with data objects like:

If you want to know more about this package, head over to the extensive documentation.

This isn't the first package that our team has made. Our website has an open source section that lists every package that our team has made. I'm pretty sure that there's something there for your next project. Currently, all of our package combined are being downloaded 10 million times a month.

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