Zend\Hydrator\Strategy

You can compose Zend\Hydrator\Strategy\StrategyInterface instances in any of the hydrators to manipulate the way they behave on extract() and hydrate() for specific key/value pairs. The interface offers the following definitions:

namespace Zend\Hydrator\Strategy;

interface StrategyInterface
{
    /**
     * Converts the given value so that it can be extracted by the hydrator.
     *
     * @param  mixed       $value The original value.
     * @param  null|object $object (optional) The original object for context.
     * @return mixed       Returns the value that should be extracted.
     */
    public function extract($value, ?object $object = null);

    /**
     * Converts the given value so that it can be hydrated by the hydrator.
     *
     * @param  mixed      $value The original value.
     * @param  null|array $data (optional) The original data for context.
     * @return mixed      Returns the value that should be hydrated.
     */
    public function hydrate($value, ?array $data = null);
}

This interface is similar to what the Zend\Hydrator\ExtractionInterface and Zend\Hydrator\HydrationInterface provide; the reason is that strategies provide a proxy implementation for hydrate() and extract() on individual values. For this reason, their return types are listed as mixed, versus as array and object, respectively.

Adding strategies to the hydrators

This package provides the interface Zend\Hydrator\Strategy\StrategyEnabledInterface. Hydrators can implement this interface, and then call on its getStrategy() method in order to extract or hydrate individual values. The interface has the following definition:

namespace Zend\Hydrator\Strategy;

interface StrategyEnabledInterface
{
    /**
     * Adds the given strategy under the given name.
     */
    public function addStrategy(string $name, StrategyInterface $strategy) : void;

    /**
     * Gets the strategy with the given name.
     */
    public function getStrategy(string $name) : StrategyInterface;

    /**
     * Checks if the strategy with the given name exists.
     */
    public function hasStrategy(string $name) : bool;

    /**
     * Removes the strategy with the given name.
     */
    public function removeStrategy(string $name) : void;
}

We provide a default implementation of the interface as part of Zend\Hydrator\AbstractHydrator; it uses an array property to store and retrieve strategies by name when extracting and hydrating values. Since all shipped hydrators are based on AbstractHydrator, they share these capabilities.

Additionally, the functionality that consumes strategies within AbstractHydrator also contains checks if a naming strategy is composed, and, if present, will use it to translate the property name prior to looking up a strategy for it.

Available implementations

Zend\Hydrator\Strategy\BooleanStrategy

This strategy converts values into Booleans and vice versa. It expects two arguments at the constructor, which are used to define value maps for true and false.

Zend\Hydrator\Strategy\ClosureStrategy

This is a strategy that allows you to pass in options for:

  • hydrate, a callback to be called when hydrating a value, and
  • extract, a callback to be called when extracting a value.

Zend\Hydrator\Strategy\DateTimeFormatterStrategy

DateTimeFormatterStrategy provides bidirectional conversion between strings and DateTime instances. The input and output formats can be provided as constructor arguments.

The strategy allows DateTime formats that use ! to prepend the format, or | or + to append it; these ensure that, during hydration, the new DateTime instance created will set the time element accordingly. As a specific example, Y-m-d| will drop the time component, ensuring comparisons are based on a midnight time value.

Starting in version 3.0, the constructor defines a third, optional argument, $dateTimeFallback. If enabled and hydration fails, the given string is parsed by the DateTime constructor, as demonstrated below:

// Previous behavior:
$strategy = new Zend\Hydrator\Strategy\DateTimeFormatterStrategy('Y-m-d H:i:s.uP');
$hydrated1 = $strategy->hydrate('2016-03-04 10:29:40.123456+01'); // Format is the same; returns DateTime instance
$hydrated2 = $strategy->hydrate('2016-03-04 10:29:40+01');        // Format is different; value is not hydrated

// Using new $dateTimeFallback flag; both values are hydrated:
$strategy = new Zend\Hydrator\Strategy\DateTimeFormatterStrategy('Y-m-d H:i:s.uP', null, true);
$hydrated1 = $strategy->hydrate('2016-03-04 10:29:40.123456+01');
$hydrated2 = $strategy->hydrate('2016-03-04 10:29:40+01');

Zend\Hydrator\Strategy\DefaultStrategy

The DefaultStrategy simply proxies everything through, without performing any conversion of values.

Zend\Hydrator\Strategy\ExplodeStrategy

This strategy is a wrapper around PHP's implode() and explode() functions. The delimiter and a limit can be provided to the constructor; the limit will only be used for extract operations.

Zend\Hydrator\Strategy\SerializableStrategy

SerializableStrategy provides the functionality backing Zend\Hydrator\ArraySerializableHydrator. You can use it with custom implementations for Zend\Serializer\Adapter\AdapterInterface if you want to as well.

Zend\Hydrator\Strategy\StrategyChain

This strategy takes an array of StrategyInterface instances and iterates over them when performing extract() and hydrate() operations. Each operates on the return value of the previous, allowing complex operations based on smaller, single-purpose strategies.

Writing custom strategies

The following example, while not terribly useful, will provide you with the basics for writing your own strategies, as well as provide ideas as to where and when to use them. This strategy simply transforms the value for the defined key using str_rot13() during both the extract() and hydrate() operations:

class Rot13Strategy implements StrategyInterface
{
    public function extract($value)
    {
        return str_rot13($value);
    }

    public function hydrate($value)
    {
        return str_rot13($value);
    }
}

This is the example class with which we want to use the hydrator example:

class Foo
{
    protected $foo = null;
    protected $bar = null;

    public function getFoo()
    {
        return $this->foo;
    }

    public function setFoo($foo)
    {
        $this->foo = $foo;
    }

    public function getBar()
    {
        return $this->bar;
    }

    public function setBar($bar)
    {
        $this->bar = $bar;
    }
}

Now, we'll add the rot13 strategy to the method getFoo() and setFoo($foo):

$foo = new Foo();
$foo->setFoo('bar');
$foo->setBar('foo');

$hydrator = new ClassMethodsHydrator();
$hydrator->addStrategy('foo', new Rot13Strategy());

When you use the hydrator to extract an array for the object $foo, you'll receive the following:

$extractedArray = $hydrator->extract($foo);

// array(2) {
//     ["foo"]=>
//     string(3) "one"
//     ["bar"]=>
//     string(3) "foo"
// }

And when hydrating a new Foo instance:

$hydrator->hydrate($extractedArray, $foo)

// object(Foo)#2 (2) {
//   ["foo":protected]=>
//   string(3) "bar"
//   ["bar":protected]=>
//   string(3) "foo"
// }

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