# Bean Parameters

Bean instances can be parameterized by a given configuration. To access the configuration add a `parameters` attribute to your bean configuration method, which holds a collection of `@Parameter` annotations.

The `@Parameter` annotation requires at least a name which will be used as key to look for in the configuration array.

In the following example the value of configuration key `test` gets passed to the bean configuration method as method parameter. The configuration parameters are passed in the same order as noted to the bean configuration method:

```php
<?php

use bitExpert\Disco\Annotations\Bean;
use bitExpert\Disco\Annotations\Parameter;
use bitExpert\Disco\Annotations\Configuration;
use bitExpert\Disco\Helper\SampleService;

/**
 * @Configuration
 */
class MyConfiguration
{
    /**
     * @Bean({
     *   "parameters"={
     *      @Parameter({"name" = "test"})
     *   }
     * })
     */
    public function mySampleService($test = '') : SampleService
    {
        $service = new SampleService();
        $service->setTest($test);
        return $service;
    }
}
```

The configuration array gets passed to the `\bitExpert\Disco\AnnotationBeanFactory` instance as second constructor parameter:

```php
<?php

$parameters = ['test' => 'This is a test.'];

$beanFactory = new \bitExpert\Disco\AnnotationBeanFactory(
  MyConfiguration::class,
  $parameters
);
\bitExpert\Disco\BeanFactoryRegistry::register($beanFactory);
```

## Default Parameter Values

Whenever a requested configuration key is not found — the key does not exist or the value is null or empty - Disco will throw an exception. This can be avoided by defining a default value that gets passed to the bean configuration method instead:

```php
<?php

use bitExpert\Disco\Annotations\Bean;
use bitExpert\Disco\Annotations\Parameter;
use bitExpert\Disco\Annotations\Configuration;
use bitExpert\Disco\Helper\SampleService;

/**
 * @Configuration
 */
class MyConfiguration
{
    /**
     * @Bean({
     *   "parameters"={
     *      @Parameter({"name" = "test", "default" = "Some default value"})
     *   }
     * })
     */
    public function mySampleService($test = '') : SampleService
    {
        $service = new SampleService();
        $service->setTest($test);
        return $service;
    }
}
```

## Default Bean Configuration Method Parameter Values

There is no need to define a default parameter for the method parameters, but if you do not provide a default value your IDE might report a problem when calling `$this->mySampleService()` without any method parameters. 

That's why it is recommended to define a default parameter for each of the bean configuration method parameters.

## Nested Configuration Array

This is possible to refer to nested configurations keys as defined like this:

```php
<?php

$parameters = [
    'nested' => [
        'key' => 'This is a test.'
    ]
];

```

Use the '.' notation to access the nested elements:

```php
<?php

use bitExpert\Disco\Annotations\Bean;
use bitExpert\Disco\Annotations\Parameter;
use bitExpert\Disco\Annotations\Configuration;
use bitExpert\Disco\Helper\SampleService;

/**
 * @Configuration
 */
class MyConfiguration
{
    /**
     * @Bean({
     *   "parameters"={
     *      @Parameter({"name" = "nested.key"})
     *   }
     * })
     */
    public function mySampleService($test = '') : SampleService
    {
        $service = new SampleService();
        $service->setTest($test);
        return $service;
    }
}
```

In this case the same rules apply for the default value handling: If one  of the nested elements is not found, the default value — if defined — gets passed to bean creation method instead. If no default value was provided, an exception gets thrown.