在数据库中存储客户端ip

我想在我的数据库中保存客户端的ip地址。下面是我的代码:

// app/Error.php
use Illuminate'Database'Eloquent'Model;
use Illuminate'Http'Request;
class Error extends Model {
    protected $fillable = array( 'code', 'user', 'error', 'client', 'call');
    public static function log( $code="unset", $message, $call="unset" ) {
        $kyu = "foobar";
        $uri = "unset";
        $ip = "unset";
        $agent = "unset";
        if ( isset( $_SERVER ) ) {
            if ( array_key_exists( 'REQUEST_URI', $_SERVER ) ) {
                $uri = $_SERVER['REQUEST_URI'];
            }
            if ( array_key_exists( 'REMOTE_ADDR', $_SERVER ) ) {
                $ip = $_SERVER['REMOTE_ADDR'];
            }
            if ( array_key_exists( 'HTTP_USER_AGENT', $_SERVER ) ) {
                $agent = $_SERVER['HTTP_USER_AGENT'];
            }
        }
        $callOnUri = $call . ' on: ' . $uri;
        // create database entry
        $user = Error::create([
            'code' => $code,
            'user' => $kyu,
            'ip' => $ip,  // this field is nullable in the migration
            'client' => $agent,
            'error' => $message,
            'call' => $callOnUri // get the call out of the request
        ]);
    }
}

当我调用这段代码时，$client和$uri被正确保存，但是$ip总是:NULL。我用以下代码检查了浏览器，在相同的请求和浏览器上，我得到了显示的IP，但在数据库中仍然是NULL

public function postRegister()
{
    $validator = $this->registrar->validator('Input::all());
    $returnVal = $this->registrar->create( 'Input::all(  ) );
    if ( is_bool($returnVal) ) {
        // foobar
    } else {
        Error::log( '1234', "Failure in the registration process.", __FUNCTION__ );
        return response()->json(["Error" => $returnVal], "server" => $_SERVER); // dump of the $_SERVER
    }
}

如何获得客户端的ip (REMOTE_ADDR)正确保存在数据库中?