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  1. Home
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  3. Components
  4. Dependency Injection
  5. Introduction to Parameters
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Introduction to Parameters

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Introduction to Parameters

You can define parameters in the service container which can then be used directly or as part of service definitions. This can help to separate out values that you will want to change more regularly.

Getting and Setting Container Parameters

Working with container parameters is straightforward using the container’s accessor methods for parameters. You can check if a parameter has been defined in the container with:

$container->hasParameter('mailer.transport');

You can retrieve a parameter set in the container with:

$container->getParameter('mailer.transport');

and set a parameter in the container with:

$container->setParameter('mailer.transport', 'sendmail');

Note

You can only set a parameter before the container is compiled. To learn more about compiling the container see Compiling the Container.

Parameters in Configuration Files

You can also use the parameters section of a config file to set parameters:

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    parameters:
    mailer.transport: sendmail
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    <parameters>
    <parameter key="mailer.transport">sendmail</parameter>
</parameters>
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    $container->setParameter('mailer.transport', 'sendmail');

As well as retrieving the parameter values directly from the container you can use them in the config files. You can refer to parameters elsewhere by surrounding them with percent (%) signs, e.g. %mailer.transport%. One use for this is to inject the values into your services. This allows you to configure different versions of services between applications or multiple services based on the same class but configured differently within a single application. You could inject the choice of mail transport into the Mailer class directly. But declaring it as a parameter makes it easier to change rather than being tied up and hidden with the service definition:

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    parameters:
    mailer.transport: sendmail

services:
    mailer:
        class:     Mailer
        arguments: ['%mailer.transport%']
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    <parameters>
    <parameter key="mailer.transport">sendmail</parameter>
</parameters>

<services>
    <service id="mailer" class="Mailer">
        <argument>%mailer.transport%</argument>
    </service>
</services>
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    use Symfony\Component\DependencyInjection\Reference;

// ...
$container->setParameter('mailer.transport', 'sendmail');
$container
    ->register('mailer', 'Mailer')
    ->addArgument('%mailer.transport%');

Caution

The values between parameter tags in XML configuration files are not trimmed.

This means that the following configuration sample will have the value \n    sendmail\n:

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<parameter key="mailer.transport">
    sendmail
</parameter>

In some cases (for constants or class names), this could throw errors. In order to prevent this, you must always inline your parameters as follow:

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<parameter key="mailer.transport">sendmail</parameter>

If you were using this elsewhere as well, then you would only need to change the parameter value in one place if needed.

You can also use the parameters in the service definition, for example, making the class of a service a parameter:

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    parameters:
    mailer.transport: sendmail
    mailer.class: Mailer

services:
    mailer:
        class:     '%mailer.class%'
        arguments: ['%mailer.transport%']
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    <parameters>
    <parameter key="mailer.transport">sendmail</parameter>
    <parameter key="mailer.class">Mailer</parameter>
</parameters>

<services>
    <service id="mailer" class="%mailer.class%">
        <argument>%mailer.transport%</argument>
    </service>

</services>
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    use Symfony\Component\DependencyInjection\Reference;

// ...
$container->setParameter('mailer.transport', 'sendmail');
$container->setParameter('mailer.class', 'Mailer');
$container
    ->register('mailer', '%mailer.class%')
    ->addArgument('%mailer.transport%');

$container
    ->register('newsletter_manager', 'NewsletterManager')
    ->addMethodCall('setMailer', array(new Reference('mailer')));

Note

The percent sign inside a parameter or argument, as part of the string, must be escaped with another percent sign:

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    arguments: ['http://symfony.com/?foo=%%s&bar=%%d']
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    <argument type="string">http://symfony.com/?foo=%%s&bar=%%d</argument>
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    ->addArgument('http://symfony.com/?foo=%%s&bar=%%d');

Array Parameters

Parameters do not need to be flat strings, they can also be arrays. For the XML format, you need to use the type="collection" attribute for all parameters that are arrays.

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    # app/config/config.yml
parameters:
    my_mailer.gateways:
        - mail1
        - mail2
        - mail3
    my_multilang.language_fallback:
        en:
            - en
            - fr
        fr:
            - fr
            - en
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    <!-- app/config/config.xml -->
<parameters>
    <parameter key="my_mailer.gateways" type="collection">
        <parameter>mail1</parameter>
        <parameter>mail2</parameter>
        <parameter>mail3</parameter>
    </parameter>
    <parameter key="my_multilang.language_fallback" type="collection">
        <parameter key="en" type="collection">
            <parameter>en</parameter>
            <parameter>fr</parameter>
        </parameter>
        <parameter key="fr" type="collection">
            <parameter>fr</parameter>
            <parameter>en</parameter>
        </parameter>
    </parameter>
</parameters>
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    // app/config/config.php
use Symfony\Component\DependencyInjection\Definition;

$container->setParameter('my_mailer.gateways', array('mail1', 'mail2', 'mail3'));
$container->setParameter('my_multilang.language_fallback', array(
    'en' => array('en', 'fr'),
    'fr' => array('fr', 'en'),
));

Constants as Parameters

The container also has support for setting PHP constants as parameters. To take advantage of this feature, map the name of your constant to a parameter key, and define the type as constant.

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    <?xml version="1.0" encoding="UTF-8"?>

<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

    <parameters>
        <parameter key="global.constant.value" type="constant">GLOBAL_CONSTANT</parameter>
        <parameter key="my_class.constant.value" type="constant">My_Class::CONSTANT_NAME</parameter>
    </parameters>
</container>
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    $container->setParameter('global.constant.value', GLOBAL_CONSTANT);
$container->setParameter('my_class.constant.value', My_Class::CONSTANT_NAME);

Note

This does not work for YAML configuration. If you’re using YAML, you can import an XML file to take advantage of this functionality:

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    # app/config/config.yml
imports:
    - { resource: parameters.xml }

PHP Keywords in XML

By default, true, false and null in XML are converted to the PHP keywords (respectively true, false and null):

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<parameters>
    <parameter key="mailer.send_all_in_once">false</parameters>
</parameters>

<!-- after parsing
$container->getParameter('mailer.send_all_in_once'); // returns false
-->

To disable this behavior, use the string type:

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<parameters>
    <parameter key="mailer.some_parameter" type="string">true</parameter>
</parameters>

<!-- after parsing
$container->getParameter('mailer.some_parameter'); // returns "true"
-->

Note

This is not available for YAML and PHP, because they already have built-in support for the PHP keywords.

Syntax for Referencing Services

You can of course also reference services, which looks a bit different in each format. You can configure the behavior if the referenced service does not exist. By default, an exception is thrown when a non-existent service is referenced.

YAML

Start the string with @ or @? to reference a service in YAML.

  • @mailer references the mailer service. If the service does not exist, an exception will be thrown;
  • @?mailer references the mailer service. If the service does not exist, it will be ignored;

Tip

Use @@ to escape the @ symbol in YAML. @@mailer will be converted into the string "@mailer" instead of referencing the mailer service.

XML

In XML, use the service type. The behavior if the service does not exist can be specified using the on-invalid argument. By default, an exception is thrown. Valid values for on-invalid are null (uses null in place of the missing service) or ignored (very similar, except if used on a method call, the method call is removed).

PHP

In PHP, you can use the Symfony\Component\DependencyInjection\Reference class to reference a service. The invalid behavior is configured using the second constructor argument and constants from Symfony\Component\DependencyInjection\ContainerInterface.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.