How to render Twig template from database in symfony2

Twig_Loader_String is deprecated and was always designed for internal use anyway. The usage of this loader is strongly discouraged.

From the API doc:

This loader should NEVER be used. It only exists for Twig internal
purposes. When using this loader with a cache mechanism, you should
know that a new cache key is generated each time a template content
“changes” (the cache key being the source code of the template). If
you don’t want to see your cache grows out of control, you need to
take care of clearing the old cache file by yourself.

Also check out this issue: https://github.com/symfony/symfony/issues/10865

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The best way I know to load a template from a String source are:

From a controller:

$template = $this->get('twig')->createTemplate('Hello {{ name }}');
$template->render(array('name'=>'World'));

as described here: http://twig.sensiolabs.org/doc/recipes.html#loading-a-template-from-a-string

From a twig template:

{{ include(template_from_string("Hello {{ name }}", {'name' : 'Peter'})) }}

as described here: http://twig.sensiolabs.org/doc/functions/template_from_string.html

Note, that the ‘template_from_string’ – function is not available by default and needs to be loaded. In symfony you would do this by adding a new service:

# services.yml
services:
    appbundle.twig.extension.string:
        class: Twig_Extension_StringLoader
        tags:
            - { name: 'twig.extension' }