The definitive guide of Symfony 1.0

5.6. Tips for Getting More from Configuration Files

There are a few last tricks to learn before writing your own YAML files. They will allow you to avoid configuration duplication and to deal with your own YAML formats.

5.6.1. Using Constants in YAML Configuration Files

Some configuration settings rely on the value of other settings. To avoid setting the same value twice, symfony supports constants in YAML files. On encountering a setting name (one that can be accessed by sfConfig::get()) in capital letters enclosed in % signs, the configuration handlers replace them with their current value. See Listing 5-20 for an example.

Listing 5-20 - Using Constants in YAML Files, Example from autoload.yml

    name:           symfony
    path:           %SF_SYMFONY_LIB_DIR%
    recursive:      on
    exclude:        [vendor]

The path parameter will take the value returned by sfConfig::get('sf_symfony_lib_dir'). If you want one configuration file to rely on another, you need to make sure that the file you rely on is already parsed (look in the symfony source to find out the order in which the configuration files are parsed). app.yml is one of the last files parsed, so you may rely on others in it.

5.6.2. Using Scriptable Configuration

It may happen that your configuration relies on external parameters (such as a database or another configuration file). To deal with these particular cases, the symfony configuration files are parsed as PHP files before being passed to the YAML parser. It means that you can put PHP code in YAML files, as in Listing 5-21.

Listing 5-21 - YAML Files Can Contain PHP

    format:  <?php echo (sfConfig::get('sf_i18n') == true ? 'xliff' : 'none')."\n" ?>

But be aware that the configuration is parsed very early in the life of a request, so you will not have any symfony built-in methods or functions to help you.

Also, as the echo language construct does not add a carriage return by default, you need to add a "\n" or use the echoln helper to keep the YAML format valid.

    format:  <?php echoln sfConfig::get('sf_i18n') == true ? 'xliff' : 'none' ?>

Caution In the production environment, the configuration is cached, so the configuration files are parsed (and executed) only once after the cache is cleared.

5.6.3. Browsing Your Own YAML File

Whenever you want to read a YAML file directly, you can use the sfYaml class. It is a YAML parser that can turn a YAML file into a PHP associative array. Listing 5-22 presents a sample YAML file, and Listing 5-23 shows you how to parse it.

Listing 5-22 - Sample test.yml File

    name:     Doe
    parents:  [John, Jane]
    children: [Paul, Mark, Simone]
    number:   34
    street:   Main Street
    city:     Nowheretown
    zipcode:  12345

Listing 5-23 - Using the sfYaml Class to Turn a YAML File into an Associative Array

$test = sfYaml::load('/path/to/test.yml');

  [house] => Array(
    [family] => Array(
      [name] => Doe
      [parents] => Array(
        [0] => John
        [1] => Jane
      [children] => Array(
        [0] => Paul
        [1] => Mark
        [2] => Simone
    [address] => Array(
      [number] => 34
      [street] => Main Street
      [city] => Nowheretown
      [zipcode] => 12345