laravel 未定义的变量：host

问：

我的问题是我在MySqlConnector.php中出现以下错误。

 Undefined variable: host error 

我使用两种不同的连接进行读/写。我根据系统使用的环境将它们合并到config/database.php文件中。这是mysql连接代码。

 <?php

switch($_SERVER['LARAVEL_ENV']){
    case 'production':

        $connections = array(
            'mysql' => array(
                'read' => array(
                    'host'  => '127.0.0.1',
                ),
                'write' => array(
                    'host'  => 'hosturl',
                ),
                'driver'    => 'mysql',
                'database'  => 'app_system',
                'username'  => 'username',
                'password'  => 'password',
                'charset'   => 'utf8',
                'collation' => 'utf8_unicode_ci',
                'prefix'    => '',
            ),

            'mysql2' => array(
                'read' => array(
                    'host'  => '127.0.0.1',
                ),
                'write' => array(
                    'host'  => 'hosturl',
                ),
                'driver'    => 'mysql',
                'database'  => 'app_userdata',
                'username'  => 'username',
                'password'  => 'password',
                'charset'   => 'utf8',
                'collation' => 'utf8_unicode_ci',
                'prefix'    => '',
            )
        );

    break;
    case 'beta':

        $connections = array(
            'mysql' => array(
                'read' => array(
                    'host'  => '127.0.0.1',
                ),
                'write' => array(
                    'host'  => 'hosturl',
                ),
                'driver'    => 'mysql',
                'database'  => 'app_system',
                'username'  => 'username',
                'password'  => 'password',
                'charset'   => 'utf8',
                'collation' => 'utf8_unicode_ci',
                'prefix'    => '',
            ),

            'mysql2' => array(
                'read' => array(
                    'host'  => '127.0.0.1',
                ),
                'write' => array(
                    'host'  => 'hosturl',
                ),
                'driver'    => 'mysql',
                'database'  => 'app_userdata',
                'username'  => 'username',
                'password'  => 'password',
                'charset'   => 'utf8',
                'collation' => 'utf8_unicode_ci',
                'prefix'    => '',
            )
        );

    break;
    case 'development':

        $connections = array(
            'mysql' => array(
                'driver'    => 'mysql',
                'host'      => 'localhost',
                'database'  => 'app_system',
                'username'  => 'root',
                'password'  => 'root',
                'charset'   => 'utf8',
                'collation' => 'utf8_unicode_ci',
                'prefix'    => '',
            ),

            'mysql2' => array(
                'driver'    => 'mysql',
                'host'      => 'localhost',
                'database'  => 'app_userdata',
                'username'  => 'root',
                'password'  => 'root',
                'charset'   => 'utf8',
                'collation' => 'utf8_unicode_ci',
                'prefix'    => '',
            )
        );

    break;
}

 return array(
'fetch'         => PDO::FETCH_CLASS,
'default'       => 'mysql',
'connections'   => $connections,
'migrations'    => 'migrations',
'redis'         => array(
    'cluster' => true,
    'default' => array(
        'host'     => '127.0.0.1',
        'port'     => 6379,
        'database' => 0,
    ),
),

);

我想做的就是使用不同的主机进行阅读，使用另一台主机进行写作。当我在 localhost 中使用一个连接时，我没有收到任何错误。但是在多个连接中，我收到错误。错误的原因是什么？