Configuration file and/or Constants, when to use?

Question

Currently I use constants to store configuration data in my application, but searching saw that it is a "bad practice" by coupling that can generate, I found some questions right here in Stackoverflow saying that the best thing to do is to put all the settings in a file (.ini, .xml, etc) and create a class to recover these values.

1 - One of the "problems" I found is when I need to use these values in views/html. For example, when loading css/js, I currently do so:

<link rel="..." href="<?=APPURL?>/public/css/...">

in which case the use of constants is correct? even because this constant "APPURL" is generated outside the configuration file, within another class that generates the friendly url dynamically.

What I built to replace the use of constants was the following:

// interface para forçar implementações de qualquer configuração que eu faça

interface ConfigHandler {

    function setConfigFile($file);

    function getConfigFile($file);

    function getConfigFileContent($file);

    function get();
}

.

// classe que recupera as configurações de um json

class jsonConfig implements ConfigHandler {

    private static $configFile = 'config.json';

    static function setConfigFile ($configFile) {

        if(isset($configFile) && is_readable($configFile))
            self::$configFile = $configFile;
        else
            throw new Exception("Arquivo '$configFile' nao encontrado");
    }

    static function getConfigFileContent () {
        return file_get_contents(self::$configFile);
    }

    static function getConfigFile () {
        return self::$configFile;
    }

    static function get($param = null) {

        $configs = json_decode(self::getConfigFileContent(), true);

        if($param)
            return $configs[$param];

        return $configs;
    }
}

.

 // caso eu precise mudar pra um arquivo xml

    class xmlConfig implements configHandler {...}

Example of use:

$host = jsonConfig::get('dbhost');
$user = jsonConfig::get('dbuser');
$pass = jsonConfig::get('dbpass');


$PDO = new PDO(...);

2 - In this case of the configuration classes, setting a constant outside the application with the file name to be read is also correct? otherwise if I wanted to change the file only by editing the class?

Answer 1

I don’t usually use that kind of constant define( 'FOO' , 'foo' ) just for using a class to work with configuration files.

At most I use constant in classes because nothing interferes with the application part.

In the configuration files I define everything and everything is in a single folder without having to 'pan' files when changing something you need - type BD password, directory...

About your doubt of <?=APPURL?>, the question is not right or wrong, but what is more practical. As I mentioned, I work with multiple configuration files, and you can have a single file with all the required constants making it easy to maintain.

Your example of using the DB config is correct, and I would also extend its use to the view and would change the value to the complete directory path: css => xxx/public/css/, js => xxx/public/js/... I see that this way it is easier to apply and do maintenance leaving as little as possible in the view.

In short, it goes from case to case.