Question

从item.php可以看出，我有2个功能来显示一些项目

display_item_1（）和display_item_2（）

当我通过调用

运行程序时

$item = new item();
$item->display_item_1(1);
$item->display_item_2(1);

它只显示function-＆gt; display_item_1（）

但是对于display_item_2（）收到致命错误：在null上调用成员函数query（）

换句话说，函数display_item_1（）和display_item_2（）都是相同的编码，但只显示第一个。那么这意味着item.php中的构造函数不正确？

或者我做错了哪一部分？

db.php中

class db{

protected $db_host;
protected $db_name;
protected $db_user_name;
protected $db_pass;

public function __construct() {
$this->db_host="localhost";
$this->db_name="bs";
$this->db_user_name="root";
$this->db_pass="";
}

public function conn(){

try {   
    $conn = new PDO("mysql:host=$this->db_host;dbname=$this->db_name", $this->db_user_name="root", $this->db_pass);
    $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    return $conn;
}
catch(PDOException $e)
    {
    echo $sql . "<br>" . $e->getMessage();
    }
}
}

item.php

require "db.php";

class item {

public $user_uid;
protected $item_name;
public $conn;

public function __construct(){
    $db = new db();
    $this->conn= $db->conn();

}

public function display_item_1($uid){

    $this->user_uid=$uid;

    try{
        $sql="SELECT * FROM item where uid='$this->user_uid'";
        $statement=$this->conn->query($sql);
    }
    catch(PDOException $e){
        ... 
    }

}

public function display_item_2($uid){

    $this->user_uid=$uid;

    try{
        $sql="SELECT * FROM item where uid='$this->user_uid'";
        $statement=$this->conn->query($sql);
        }

    }
    catch(PDOException $e){
        ...
    }

}
}

Answer 1

在你的另一个问题中也提到过，我将在这个问题中再次提到它：重写你的代码并让DB类处理查询。现在你的数据库类在面向对象的设计方面没有意义，它编写得不好，应该从头开始重写。以下只是一个想法：

<强> db.php中

// Use uppercase for class names and stick to possibly unreserved names
class DatabaseHandler
{

    // moved from constructor and set to private, you are surely not using inheritance
    private $db_host="localhost";
    private $db_name="bs";
    private $db_user_name="root";
    private $db_pass="";
    private $connection= FALSE; // added, holds db connection

    /* obsolete in your case 
    public function __construct() { }
    */

    public function connect() 
    {

        try {   
            $conn = new PDO("mysql:host=$this->db_host;dbname=$this->db_name", $this->db_user_name="root", $this->db_pass);
            $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $this->connection= $conn;
            return TRUE;
        }
        catch(PDOException $e)
        {
            echo $sql . "<br>" . $e->getMessage();
            return FALSE;
        }
    }

    /**
    * return records from your database; checks skipped in this example
    */
    public function query($query) 
    {
        // only query if a database connection is available, else return false
        if (!$this->connection) return FALSE;
        try {
            $statement=$this->connection->query($query);
            return $statement->fetchAll();
        }
        catch(PDOException $e){
            // logging or whatever ...
            return FALSE;           
        }
    }
}

<强> item.php

class Item {

    public $user_uid;
    private $item_name;
    private $conn; // why make it public?

    public function __construct(){
        $db = new DatabaseHandler();
        if (!$db->connect()) die("Database not available"); // update these lines
        $this->conn= $db; 
    }

    public function display_item_1($uid){
        $this->user_uid=$uid;

        $arrValues= $this->conn->query("SELECT * FROM item where uid='$this->user_uid'");
        print_r($arrValues);
    }

    public function display_item_2($uid){
        $this->user_uid=$uid;

        $arrValues= $this->conn->query("SELECT * FROM item where uid='$this->user_uid'");
        print_r($arrValues);
    }
}

运行代码：

$item = new Item();
$item->display_item_1(1);
$item->display_item_2(1);

请仔细阅读一些教程，尤其是类和OOP（面向对象编程）。

php构造函数无效，错误查询（）为null

1 个答案: