致命错误:调用成员函数query() PHP CLASS

Question

我想写这个类来连接和查询我的数据库，但我得到了这个错误:

致命错误:在null对象上调用成员函数query()C:xxxxxx xxxxxxxxxx xxxxxxxpagesconfigclass.php on line 24

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>";
    }  

不从方法返回$connection，所以其他方法调用失败，这样做:

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
    }  

如前所述，您的代码效率不高，因为对于执行的每个查询，代码(重新)连接到DB。这是不必要的昂贵/低效的。

有很多方法可以解决这个问题。

1. 在DB类实例化时连接到DB

如

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，即仅在第一次执行查询时连接

如

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初始化连接会更好，目前每次使用query方法都要打开一个到数据库的新连接。

编辑:你的类看起来像这样

<?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');
?>

我认为不需要静态的属性，所以我也改变了它们。

db_query方法在我看来太不灵活，因为它直接输出您的结果。我将使用fetch_all返回整个结果集作为一个数组。这样，您就可以自由选择如何处理您的结果。