php - fatal error : Call to a member function query() PHP CLASS

Question

我正在尝试编写此类来连接和查询我的数据库，但出现此错误:

Fatal error: Call to a member function query() on null in C:\xxxxxx\xxxx\xxxxx\xxxxxxx\pages\config\class.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>";

    }  

不会从方法中重新调整 $connection，因此其余方法调用失败，请执行此操作:

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
    }  

如前所述，您的代码效率不高，因为对于执行的每个查询，代码都会(重新)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。

1. 在数据库类实例化时连接到数据库

例如

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;
    }  
}

1. 惰性连接，即只在第一次执行查询时连接

例如

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>";
        }
    }
}