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  4. Introduction to Parameters

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Read the updated version of this page for Symfony 5.3 (the current stable version).

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.

Parameters in Configuration Files

Use the parameters section of a config file to set parameters:

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    parameters:
    mailer.transport: sendmail
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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"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

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

You can refer to parameters elsewhere in any config file 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:
    app.mailer:
        class:     AppBundle\Mailer
        arguments: ['%mailer.transport%']
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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"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

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

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

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

$container->register('app.mailer', 'AppBundle\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>

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>http://symfony.com/?foo=%%s&amp;bar=%%d</argument>
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    ->addArgument('http://symfony.com/?foo=%%s&bar=%%d');

Getting and Setting Container Parameters in PHP

Working with container parameters is straightforward using the container’s accessor methods for parameters:

// check if a parameter is defined
$container->hasParameter('mailer.transport');

// get value of a parameter
$container->getParameter('mailer.transport');

// add a new parameter
$container->setParameter('mailer.transport', 'sendmail');

Caution

The used . notation is just a Symfony convention to make parameters easier to read. Parameters are just flat key-value elements, they can’t be organized into a nested array

Note

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

Array Parameters

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

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    parameters:
    my_mailer.gateways: [mail1, mail2, mail3]

    my_multilang.language_fallback:
        en:
            - en
            - fr
        fr:
            - fr
            - en
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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"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <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>
</container>
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    $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 XML and PHP formats also have 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"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <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);

Tip

If you’re using YAML, you can import an XML file to take advantage of this functionality:

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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</parameter>
</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.

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