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:
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$container->hasParameter('mailer.transport');
You can retrieve a parameter set in the container with:
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$container->getParameter('mailer.transport');
and set a parameter in the container with:
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$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:
- YAML
- XML
- PHP
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parameters:
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:
- YAML
- XML
- PHP
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parameters:
mailer.transport: sendmail
services:
mailer:
class: Mailer
arguments: ['%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:
- YAML
- XML
- PHP
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parameters:
mailer.transport: sendmail
mailer.class: Mailer
services:
mailer:
class: '%mailer.class%'
arguments: ['%mailer.transport%']
Note
The percent sign inside a parameter or argument, as part of the string, must be escaped with another percent sign:
- YAML
- XML
- PHP
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arguments: ['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.
- YAML
- XML
- PHP
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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
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
.
- XML
- PHP
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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>
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:
- YAML
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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 themailer
service. If the service does not exist, an exception will be thrown;@?mailer
references themailer
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 Reference class to reference a service. The invalid behavior is configured using the second constructor argument and constants from ContainerInterface.