警告:mysqli_query()期望参数1为mysqli, null

Question

我在一个新的PHP网站工作，我需要这个错误的帮助。

警告:mysqli_query()期望参数1为mysqli, null给定在. .

我有类Database.class，和一个抽象类ActiveRecord.php.

    class Database {
    private static $instance = null;
    private function __construct(){}
    public static function getInstance(){
        if(!self::$instance){
            self::$instance = mysqli_connect(DBHOST, DBUSER, DBPASS, DB);
            return self::$instance;
        }
    }
}

和ActiveRecord类在新文件。

        abstract class ActiveRecord {
    public function save() {
        $q = "UPDATE " . static::$table . " SET ";
        foreach($this as $k=>$v){
            if($k==static::$key) continue;
            $q.=$k."='".$v."',";
        }
        $q = rtrim($q,",");
        $keyField = static::$key;
        $q.=" WHERE ".static::$key." = " . $this->$keyField;
        mysqli_query(Database::getInstance(), $q);
    }
}

当我测试save();函数我得到警告mysqli。我创建了一个新文件，并把这个写在里面。

    class Category extends ActiveRecord {
    public static $table = "categories";
    public static $key = "category_id";
}
$cat = Category::get(1);
$cat->name = "Action";
$cat->description = "Action Description";
$cat->save();

问题是在save()函数Database::getInstane()不被识别。但是，如果我把"mysqli_connect("localhost"，"root"，"，"db")"一切工作正常，脚本更新数据库记录。

有谁知道是什么问题吗?

Answer 1

问题是如果实例已经创建，则不返回任何内容。

更新你的getInstance函数如下

public static function getInstance(){
if(!self::$instance){ 
self::$instance = mysqli_connect(DBHOST, DBUSER, DBPASS, DB);
} 
return self::$instance; 
 }