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Recipes

Making a Layout conditional

Working with Ajax means that the same content is sometimes displayed as is, and sometimes decorated with a layout. As Twig layout template names can be any valid expression, you can pass a variable that evaluates to true when the request is made via Ajax and choose the layout accordingly:

{% extends request.ajax ? "base_ajax.html" : "base.html" %}

{% block content %}
    This is the content to be displayed.
{% endblock %}

Making an Include dynamic

When including a template, its name does not need to be a string. For instance, the name can depend on the value of a variable:

{% include var ~ '_foo.html' %}

If var evaluates to index, the index_foo.html template will be rendered.

As a matter of fact, the template name can be any valid expression, such as the following:

{% include var|default('index') ~ '_foo.html' %}

Overriding a Template that also extends itself

A template can be customized in two different ways:

  • Inheritance: A template extends a parent template and overrides some blocks;
  • Replacement: If you use the filesystem loader, Twig loads the first template if finds in a list of configured directories; a template found in a directory replaces another one from a directory further in the list.

But how do you combine both: replace a template that also extends itself (aka a template in a directory further in the list)?

Let's say that your templates are loaded from both .../templates/mysite and .../templates/default in this order. The page.twig template, stored in .../templates/default reads as follows:

{# page.twig #}
{% extends "layout.twig" %}

{% block content %}
{% endblock %}

You can replace this template by putting a file with the same name in .../templates/mysite. And if you want to extend the original template, you might be tempted to write the following:

{# page.twig in .../templates/mysite #}
{% extends "page.twig" %} {# from .../templates/default #}

Of course, this will not work as Twig will always load the template from .../templates/mysite.

It turns out it is possible to get this to work, by adding a directory right at the end of your template directories, which is the parent of all of the other directories: .../templates in our case. This has the effect of making every template file within our system uniquely addressable. Most of the time you will use the "normal" paths, but in the special case of wanting to extend a template with an overriding version of itself we can reference its parent's full, unambiguous template path in the extends tag:

{# page.twig in .../templates/mysite #}
{% extends "default/page.twig" %} {# from .../templates #}

Note

This recipe was inspired by the following Django wiki page: http://code.djangoproject.com/wiki/ExtendingTemplates

Customizing the Syntax

Twig allows some syntax customization for the block delimiters. It's not recommended to use this feature as templates will be tied with your custom syntax. But for specific projects, it can make sense to change the defaults.

To change the block delimiters, you need to create your own lexer object:

$twig = new Twig_Environment();

$lexer = new Twig_Lexer($twig, array(
    'tag_comment'  => array('{#', '#}'),
    'tag_block'    => array('{%', '%}'),
    'tag_variable' => array('{{', '}}'),
));
$twig->setLexer($lexer);

Here are some configuration example that simulates some other template engines syntax:

// Ruby erb syntax
$lexer = new Twig_Lexer($twig, array(
    'tag_comment'  => array('<%#', '%>'),
    'tag_block'    => array('<%', '%>'),
    'tag_variable' => array('<%=', '%>'),
));

// SGML Comment Syntax
$lexer = new Twig_Lexer($twig, array(
    'tag_comment'  => array('<!--#', '-->'),
    'tag_block'    => array('<!--', '-->'),
    'tag_variable' => array('${', '}'),
));

// Smarty like
$lexer = new Twig_Lexer($twig, array(
    'tag_comment'  => array('{*', '*}'),
    'tag_block'    => array('{', '}'),
    'tag_variable' => array('{$', '}'),
));

Using dynamic Object Properties

When Twig encounters a variable like article.title, it tries to find a title public property in the article object.

It also works if the property does not exist but is rather defined dynamically thanks to the magic __get() method; you just need to also implement the __isset() magic method like shown in the following snippet of code:

class Article
{
    public function __get($name)
    {
        if ('title' == $name)
        {
            return 'The title';
        }

        // throw some kind of error
    }

    public function __isset($name)
    {
        if ('title' == $name)
        {
            return true;
        }

        return false;
    }
}

Accessing the parent Context in Nested Loops

Sometimes, when using nested loops, you need to access the parent context. The parent context is always accessible via the loop.parent variable. For instance, if you have the following template data:

$data = array(
    'topics' => array(
        'topic1' => array('Message 1 of topic 1', 'Message 2 of topic 1'),
        'topic2' => array('Message 1 of topic 2', 'Message 2 of topic 2'),
    ),
);

And the following template to display all messages in all topics:

{% for topic, messages in topics %}
    * {{ loop.index }}: {{ topic }}
  {% for message in messages %}
      - {{ loop.parent.loop.index }}.{{ loop.index }}: {{ message }}
  {% endfor %}
{% endfor %}

The output will be similar to:

* 1: topic1
  - 1.1: The message 1 of topic 1
  - 1.2: The message 2 of topic 1
* 2: topic2
  - 2.1: The message 1 of topic 2
  - 2.2: The message 2 of topic 2

In the inner loop, the loop.parent variable is used to access the outer context. So, the index of the current topic defined in the outer for loop is accessible via the loop.parent.loop.index variable.

Defining undefined Functions and Filters on the Fly

When a function (or a filter) is not defined, Twig defaults to throw a Twig_Error_Syntax exception. However, it can also call a callback (any valid PHP callable) which should return a function (or a filter).

For filters, register callbacks with registerUndefinedFilterCallback(). For functions, use registerUndefinedFunctionCallback():

// auto-register all native PHP functions as Twig functions
// don't try this at home as it's not secure at all!
$twig->registerUndefinedFunctionCallback(function ($name) {
    if (function_exists($name)) {
        return new Twig_Function_Function($name);
    }

    return false;
});

If the callable is not able to return a valid function (or filter), it must return false.

If you register more than one callback, Twig will call them in turn until one does not return false.

Tip

As the resolution of functions and filters is done during compilation, there is no overhead when registering these callbacks.

Validating the Template Syntax

When template code is providing by a third-party (through a web interface for instance), it might be interesting to validate the template syntax before saving it. If the template code is stored in a $template variable, here is how you can do it:

try {
    $twig->parse($twig->tokenize($template));

    // the $template is valid
} catch (Twig_Error_Syntax $e) {
    // $template contains one or more syntax errors

Refreshing modified Templates when APC is enabled and apc.stat = 0

When using APC with apc.stat set to 0 and Twig cache enabled, clearing the template cache won't update the APC cache. To get around this, one can extend Twig_Environment and force the update of the APC cache when Twig rewrites the cache:

class Twig_Environment_APC extends Twig_Environment
{
    protected function writeCacheFile($file, $content)
    {
        parent::writeCacheFile($file, $content);

        // Compile cached file into bytecode cache
        apc_compile_file($file);
    }
}