Custom Value Resolvers

Custom value resolvers in PHP AutoMapper provide a way to customize how a specific property or value is resolved during the mapping process. This can be particularly useful when the value of a property depends on some complex logic or external factors.

There are several reasons why you might want to use custom value resolvers:

• Complex Logic: If the value of a property depends on some complex logic, you can encapsulate this logic in a custom value resolver.
• External Factors: If the value of a property depends on external factors (like the current time, a value from a database, etc.), you can use a custom value resolver to handle this.
• Code Organization: Custom value resolvers allow you to keep your mapping configurations clean and focused on the mapping itself, while offloading complex value resolution to separate classes.

How to Create a Custom Value Resolvers

Anonymous Function

Use an anonymous function to define custom value resolution logic directly in your mapping configuration and pass it to the mapFrom() options method.

Here's an example:

use Backbrain\Automapper\Contract\Builder\Config;
use Backbrain\Automapper\MapperConfiguration;

$config = new MapperConfiguration(fn (Config $config) => $config
    ->createMap(SourceClass::class, DestinationClass::class)
        ->forMember(
            'passwordHash', 
            fn (Options $opts) => $opts->mapFrom(
                fn (SourceClass $source, ResolutionContextInterface $context) => hash('argon2id', $source->passwordPlain)
            )
        )
);

The ValueResolverInterface

To create a custom value resolver, you need to create a class that implements the ValueResolverInterface. This interface has a single method resolve that you need to implement.

Here's an example:

use Backbrain\Automapper\Contract\ValueResolverInterface;
use Backbrain\Automapper\Contract\ResolutionContextInterface;

class CustomValueResolver implements ValueResolverInterface
{
    public function resolve(object $source, ResolutionContextInterface $context): mixed
    {
        // Implement your custom value resolution logic here.
        // For example, let's assume we are calculating a value based on some properties of the source object.
        return hash('argon2id', $source->passwordPlain);
    }
}

In this example, CustomValueResolver is implementing ValueResolverInterface. The resolve method is responsible for calculating a value based on the properties of the source object.

To use this custom value resolver in your mapping configuration, you can use the valueProvider method:

use Backbrain\Automapper\Contract\Builder\Config;
use Backbrain\Automapper\MapperConfiguration;

$config = new MapperConfiguration(fn (Config $config) => $config
    ->createMap(SourceClass::class, DestinationClass::class)
        ->forMember('passwordHash', fn (Options $opts) => $opts->mapFrom(new CustomValueResolver()))
);

In this configuration, AutoMapper will use CustomValueResolver to resolve the value of the passwordHash when mapping SourceClass to DestinationClass.