Question

我正在尝试编写此类来连接和查询我的数据库，但是我收到了这个错误：

致命错误：在null中调用成员函数query（）第24行的C：\ xxxxxx \ xxxx \ xxxxx \ xxxxxxx \ pages \ config \ class.php

Php代码：

<?php

class Db{

    private static $db_host = "localhost";
    private static $db_user = "root";
    private static $db_pass = "";
    private static $db_name = "sivi";

    public $connection;

        public function db_connect() {    

            $connection = mysqli_connect(self::$db_host, self::$db_user, self::$db_pass, self::$db_name) or die("Error " . mysqli_error($connection)); 
            echo "Conexión realizada". "<br>";

    }  

    public function db_query($query){

          $connection = $this->db_connect();
          var_dump($query);
          $result = $connection->query($query);
          while($row = mysqli_fetch_array($result)) { 
          echo $row["COD_PRE"] . "<br>";
          }

    } 

}

$con = new Db();
$con->db_query('SELECT `COD_PRE`, `CODE` FROM `test` WHERE `CODE` = 457 AND CONFIN = 1');

?>

Answer 1

你的方法：

public function db_connect() {    

            $connection = mysqli_connect(self::$db_host, self::$db_user, self::$db_pass, self::$db_name) or die("Error " . mysqli_error($connection)); 
            echo "Conexión realizada". "<br>";

    }

不会从方法返回$connection，因此其余方法调用失败，请执行以下操作：

public function db_connect() {    

            $connection = mysqli_connect(self::$db_host, self::$db_user, self::$db_pass, self::$db_name) or die("Error " . mysqli_error($connection)); 
            echo "Conexión realizada". "<br>";
           return $connection; // return the $connection object
    }

如上所述，您的代码效率不高，因为执行的每个查询代码（重新）都连接到数据库。这是不必要的昂贵/低效。

有很多方法可以解决这个问题。

在数据库类

e.g

class Db{

    private static $db_host = "localhost";
    private static $db_user = "root";
    private static $db_pass = "";
    private static $db_name = "sivi";

    public $connection;

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

    public function db_connect() {    

            $connection = mysqli_connect(self::$db_host, self::$db_user, self::$db_pass, self::$db_name) or die("Error " . mysqli_error($connection)); 
            echo "Conexión realizada". "<br>";
            return $connection;
    }  
}

延迟连接，即仅在第一次执行的查询时连接

e.g

class Db{

    private static $db_host = "localhost";
    private static $db_user = "root";
    private static $db_pass = "";
    private static $db_name = "sivi";
    public $connection = null;
    public function __construct()
    {
    }  
    public function db_connect() {    
        $connection = mysqli_connect(self::$db_host, self::$db_user, self::$db_pass, self::$db_name) or die("Error " . mysqli_error($connection)); 
        echo "Conexión realizada". "<br>";
        return $connection;
    }  
    public function db_query($query){
        if ( null ==== $this->connection ) $this->connection = $this->db_connect();
        var_dump($query);
        $result = $this->connection->query($query);
        while($row = mysqli_fetch_array($result)) { 
            echo $row["COD_PRE"] . "<br>";
        }
    }
}

Answer 2

您必须使用$this来访问自己类的属性。

$this->connection = ....

$result = $this->connection->...

如果使用构造函数来启动连接会更好，目前每次使用查询方法时都会打开与数据库的新连接。

编辑：你的课程看起来像这样

<?php

class Db {

    private $db_host = "localhost";
    private $db_user = "root";
    private $db_pass = "";
    private $db_name = "sivi";
    private $connection;

    public function __construct() {
        $this->connection = mysqli_connect($this->db_host, $this->db_user, $this->db_pass, $this->db_name) 
                or die("Error " . mysqli_error($this->connection));
    }

    public function db_query($query) {
        var_dump($query);
        $result = $this->connection->query($query);
        while ($row = mysqli_fetch_array($result)) {
            echo $row["COD_PRE"] . "<br>";
        }
    }

}

$con = new Db();
$con->db_query('SELECT `COD_PRE`, `CODE` FROM `test` WHERE `CODE` = 457 AND CONFIN = 1');
?>

我认为属性不需要是静态的，所以我也改变了它们。

db_query方法在我看来太不灵活，因为它直接输出你的结果。我会使用fetch_all将整个结果集作为数组返回。这样您就可以自由选择处理结果的方式。

致命错误：调用成员函数query（）PHP CLASS

2 个答案: