php - 调用非对象的成员函数 InnerJoin()

Question

我是 PHP 的新手，我正在尝试创建一个具有内部连接功能的数据库类，但我收到了这个错误:

Call to a member function InnerJoin() on a non-object in C:\xampp\htdocs\world\index.php on line 10

我的代码:

<?php 

class DB {
private static $_link = null,
               $_host = "127.0.0.1",
               $_pass = "",
               $_dbname = "mundo",
               $_user = "root",
               $_charset = "utf8";
private $_pdo,
        $_query,
        $_count = 0,
        $_error = false,
        $_results;

private function __construct() {
    $this->_pdo = new PDO("mysql:host=".self::$_host.";dbname=".self::$_dbname,self::$_user,self::$_pass);
}

public static function getLink() {
    if(!isset(self::$_link)) {
        self::$_link = new DB();
    }
    return self::$_link;
}

public function Get($table) {
    return $this->_query = "SELECT * FROM ".$table;
}

public function Go() {
    if($this->_query = $this->_pdo->prepare($sql)) {
        echo "prepared";
    }
}

public function InnerJoin($table1, $column1, $table2, $column2){
    return $this->_query = $this->_query." INNER JOIN ".$table2." ON ".$table1.".".$column1." = ".$table2.".".$column2;
}
}
?>

在我的 index.php 中我有这个:

<?php 
$DB = DB::getLink()->Get("paises")->InnerJoin("paises","Id_Continente","Continentes","Id_Continente")->Go();
?>

希望你能帮帮我，谢谢

Answer 1

因为您要从 Get 函数返回 $this->_query，因为它需要返回一个完整的对象才能再次使用它，

public function Get($table) {
    $this->_query = "SELECT * FROM ".$table;
    return $this;
}

有关详细信息，请阅读 Method Chaining .