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Adding lazy services documentation as of symfony/symfony#7890 #2619

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1 change: 1 addition & 0 deletions components/dependency_injection/index.rst
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Expand Up @@ -14,5 +14,6 @@
configurators
parentservices
advanced
lazy_services
workflow

67 changes: 67 additions & 0 deletions components/dependency_injection/lazy_services.rst
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.. index::
single: Dependency Injection; Lazy Services

Lazy Services
=============

.. versionadded:: 2.3
Lazy services were added in Symfony 2.3.

Configuring lazy services
-------------------------

In some particular cases where a very heavy service is always requested,
but not always used, you may want to mark it as ``lazy`` to delay its instantiation.

In order to have services to lazily instantiate, you will first need to install
the `ProxyManager bridge`_:

.. code-block:: bash
$ php composer.phar require symfony/proxy-manager-bridge:2.3.*
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This will be useless for people using the fullstack repo (as they already have the bridge in it). however, they need to require ProxyManager.

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Are you sure? You are aware it's a components article? As far as I can see, this package is part of the the 'suggested' packages in de di component, it's not a required package.

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ah sorry, I forgot we are in the component section.

but this should still be noted IMO. Because for people installing the full symfony package, they need to require ProxyManager to get it

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yeah, but people having the full stack repo don't have a requirement on it as symfony/symfony does not define it as a requirement (it is not a mandatory dependency of the full repo as we don't want to force everyone to get it)

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@stof wondering how composer behaves here... Guess it marks it as already installed. Forcing installation of ocramius/proxy-manager:* is kinda "meh" here (because of *), and keeping this document up to date with the correct supported version is meh too ;)


You can mark the service as ``lazy`` by manipulating its definitions:

.. configuration-block::

.. code-block:: yaml

services:
foo:
class: Acme\Foo
lazy: true

.. code-block:: xml

<service id="foo" class="Acme\Foo" lazy="true" />

.. code-block:: php

$definition = new Definition('Acme\Foo');
$definition->setLazy(true);
$container->setDefinition('foo', $definition);
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I prefer

$container->register('foo', 'Acme\Foo')
    ->setLazy(true);


You can then require the service from the container::

$service = $container->get('foo');

At this point the retrieved ``$service`` should be a virtual `proxy`_ with the same
signature of the class representing the service.

.. note::

If you don't install the `ProxyManager bridge`_, the container will just skip
over the ``lazy`` flag and simply instantiate the service as it would normally do.

The proxy gets initialized and the actual service is instantiated as soon as you interact
in any way with this object.

Additional Resources
--------------------

You can read more about how proxies are instantiated, generated and initialized in
the `documentation of ProxyManager`_.


.. _`ProxyManager bridge`: https://github.com/symfony/symfony/tree/2.3/src/Symfony/Bridge/ProxyManager
.. _`proxy`: http://en.wikipedia.org/wiki/Proxy_pattern
.. _`documentation of ProxyManager`: https://github.com/Ocramius/ProxyManager/blob/master/docs/lazy-loading-value-holder.md
1 change: 1 addition & 0 deletions components/map.rst.inc
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Expand Up @@ -39,6 +39,7 @@
* :doc:`/components/dependency_injection/configurators`
* :doc:`/components/dependency_injection/parentservices`
* :doc:`/components/dependency_injection/advanced`
* :doc:`/components/dependency_injection/lazy_services`
* :doc:`/components/dependency_injection/workflow`

* **DOM Crawler**
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