php - OOP MySQLi 连接

Question

我是 OOP 的新手。我有类数据库

class Database{
private $host;
private $user;
private $pass;
private $db;
public $mysqli;

function db_connect(){
    $this->host = 'localhost';
    $this->user = 'root';
    $this->pass = '';
    $this->db = 'db';

    $this->mysqli = new mysqli($this->host, $this->user, $this->pass, $this->db);
    return $this->mysqli;
}

在类数据库中，我有函数 db_​​num

function db_num($sql){
    $num = mysqli_num_rows(mysqli_query($this->mysqli,"{$sql}"));
    return $num;
}

但是当我在 con 参数 $this->mysqli 中使用时它无法连接到数据库

Answer 1

混合使用 mysqli 对象样式和程序样式是不好的做法。

尝试这个:

function db_num($sql){
    $result = $this->mysqli->query($sql);
    return $result->num_rows;
}

调用 db_num()之前一定要连接数据库，例如:

$db = new Database();
$db->db_connect();
$db->db_num("SELECT fields FROM YourTable");

我认为更简洁的方法是调用 db_connect在构造函数内部:

class Database{
  private $host;
  private $user;
  private $pass;
  private $db;
  public $mysqli;

  public function __construct() {
    $this->db_connect();
  }

  private function db_connect(){
    $this->host = 'localhost';
    $this->user = 'root';
    $this->pass = '';
    $this->db = 'db';

    $this->mysqli = new mysqli($this->host, $this->user, $this->pass, $this->db);
    return $this->mysqli;
  }

  public function db_num($sql){
        $result = $this->mysqli->query($sql);
        return $result->num_rows;
  }
}

$db = new Database();
$db->db_num("SELECT fields FROM YourTable");