使用ArrayObject在PHP中可强制执行的数组结构？

Question

I've a set of data (~30 properties, all having their own array of values) that I want to pass around to various classes in PHP and I want to also enforce the data's array structure. Multiple classes will be expecting this structure to be consistent.

Because of these facts I can't really rely on a standard array and so I decided to pass an object around. I looked into ArrayObject and while it allows me to set/get as if the class were an array I didn't see anything about enforcing the structure.

Is there an existing standard class that can handle enforcement of it's array-like structure while still being treated as an array, eg, basically ArrayObject + enforcement?

An example of the array structure:

$item_type_props = array(
    'phone'     => array('speed' => 1000, 'self_label' => false, 'support_poe' => true, 'bluetooth' => false),
    'pbx'       => array('acd_support' => true, 'max_conn' => 300, max_phones => 600),
    'adapter'   => array('fxo' => 4, 'fxs' => 0, 't1_e1_pri' => 0),
    etc...
);

I know each property in the array could be it's own class and enforce it's own fields through the constructor and set/get but then I suddenly have ~30 classes that are nothing but a bunch of attributes and that seems somewhat excessive for just holding data.

---

Alternatively, if I'm just approaching this from the wrong mindset and missing something really, really obvious then please do point it out. I get the feeling that I am but my brain might be having a vacation.

Answer 1

While you could roll your own, I encourage you to use an existing validation implementation. For example, Symfony\\Validator allows you to define nested structures and the requirements on each level:

use Symfony\Component\Validator\Validation;
use Symfony\Component\Validator\Constraints as Assert;

$validator = Validation::createValidator();

$constraint = new Assert\Collection(array(
    // the keys correspond to the keys in the input array
    'name' => new Assert\Collection(array(
      'first_name' => new Assert\Length(array('min' => 101)),
      'last_name' => new Assert\Length(array('min' => 1)),
    )),
    'email' => new Assert\Email(),
    'simple' => new Assert\Length(array('min' => 102)),
    'gender' => new Assert\Choice(array(3, 4)),
    'file' => new Assert\File(),
    'password' => new Assert\Length(array('min' => 60)),
));

$violations = $validator->validate($input, $constraint);

This lets you push the details of how to validate down to another (already tested) level, while letting your code focus on why it needs this data. For the Symfony case, you can use an array as the storage mechanism, and use a design that firewalls unvalidated from validated data.

---

One way we might do this is notationally. Pretend we have implemented a method, perhaps using Symfony's validator, to return a validated array. We can use Hungarian notation to indicate our structure has passed through validation and is "safe":

<?php
$vInput = validate($_GET); // Hungarian notation: any variable beginning with "v" is "validated" and safe to use

function foobar(array $vInput) { ... }

While this is performant, it's not great for maintenance in the long term. So, you might consider an object wrapper that allows you to leverage the type system:

use Symfony\Component\Validator\Validation;
use Symfony\Component\Validator\Constraints as Assert;

class ValidatedArray extends \ArrayObject {
    public function construct($input = [], $flags = 0, $iterator_class = 'ArrayIterator') {
        $violations = Validation::createValidator()->validate($array, $this->constraints());
        // throw exception if any violations
        parent::__construct($input, $flags, $iterator_class);
    }

    public function __offsetSet($index, $value) {
        $constraints = $this->constraints()[$index]; // specific constraints to this index
        $violations = Validation::createValidator()->validate($array, $constraints);
        // throw exception on violations
        parent::__offsetSet($index, $value);
    }

    public function constraints() {
        return new Assert\Collection(...);
    }
}

$input = new ValidatedArray($_REQUEST); // first time validation
$input['foo'] = 'bar'; // also subject to validation

You might want to make this implementation an abstract base class, with concrete descendants implementing the constraints method to provide the specific limitations on the array object itself. This provides a flexible way to get dedicated Data Transfer Objects.

Answer 2

Generally speaking I would argue that - unless you are passing data to another context, eg javascript - a PHP application should be nicely organized in PHP classes. This is simply the easiest way to enforce the structure. Your are right, this might result in quite straightforward DTO's with a bunch of getters and setters, but it will beat checking array structures for sure. In your case there also appears to be a relationship in the array, otherwise it would not make sense combining them into an array at all.

Using PHP7 you can clearly define the method signature and enforce the types, eg

public function setSomething(string $myValue)
{
    $this->something = $myValue;
}

Same with return types:

public function myActionMethod(array $options): ActionRespsonse
{
    // Do something
}

If you have more complex data types, I would recommend using Value Objects. These are nothing more but simple PHP classes that represent a more complex value. For example, a phone number:

public function setPhoneNumber(PhoneNumber $phoneNumber)
{
    $this->phoneNumber = $phoneNumber;
}

Here the PhoneNumber is a Value Object which effectively is a tiny class by itself which enforces its usage:

class PhoneNumber {
    private $phoneNumber;

    public __construct(string $phoneNumber) {
        if (strlen($phoneNumber) != 10) {
            throw new \Exception('Not a valid phone number');
        }

        $this->phoneNumber = $phoneNumber;
     }
}

This is also where the validation can tie into the answer from @bishop as you can use an existing Validator to help you out. You can find an example of a Value Object of a Phone Number here (just googled it): Example Phone Number Value Object

I do have the feeling that you might be converting your PHP data to an array for another reason? Like interacting with a database, or passing it on to a different context, such as Javascript?

In that case, once you have your DTO's and VO's neatly defined you can then consider serializing them eg to/from JSON. You can use Symfony libraries for that, as described here: Symfony Serializer

If you really want arrays you can also consider hydrating them to/from entities, using the library from Marco Pivetta (ocramius) who is pretty much the authority on hydration an approach extensively used in Doctrine: Ocramius Hydrator

Plenty of options, eh!?

To be honest, though, IMHO typically there would need to be a pretty good argument to pass these complex arrays around as arrays offer very little in supporting functionality. In addition, your code will very likely and very quickly become difficult to read and maintain, as at every point where there would be some kind of modification of the array, or usage of its data elements, you would need to implement all kinds of checks or run a validation as described by @bishop. I would not allow something like that to exist in our applications code bases...

So, concluding: If you have a tightly defined set of PHP Objects with well established constructor, properties, getters, setters, constructor, relationships, action methods and besides that some kind of serializing mechanism, you're in good shape. Also other developers will be 'forced' to work with the objects and provided interface (methods and VO's) thus guaranteeing a degree of maintainability and quality.

By the way, you might consider reasing Martin Fowler's thoughts about these things: Martin Fowler: DTO Martin Fowler: VO Martin Fowler: DTO2