在 null 上调用成员函数 query()；使用 pdo

Question

我有这个错误

Call to a member function query() on null in admin.php on line 36, functicon showMenu_type_1(), query on null...........

当使用这两个php文件时：

connect.php

<?php 
class Connection{

    protected $db;

    public function Connection(){

    $conn = NULL;

        try{
            $conn = new PDO('mysql:host=localhost;dbname=home', 'root', '');
            $conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
            $conn->exec("SET CHARACTER SET utf8");      // Sets encoding UTF-8
            } catch(PDOException $e){
                echo 'ERROR: ' . $e->getMessage();
                }    
            $this->db = $conn;
    }

    public function getConnection(){
        return $this->db;
    }
}
$pd = new Connection();
?>

admin.php

<?php
    require_once('form.php');
    require_once('connect.php');
    error_reporting(E_ALL & ~E_NOTICE & ~E_DEPRECATED);
    ?>
    <?php 
    /**
    * 
    */
    $pdo= $pd->getConnection();
    class menu_multi
    {

        function showMenu_type_1(){       
            $sql_1 =$pdo->query("SELECT * FROM category WHERE menu_parent_id = 0 && type= 'MT01'");
}
}

Answer 1

它为空，因为 $pd 是全局的，您必须在函数中明确说明。

<?php
require_once('connect.php');
error_reporting(E_ALL & ~E_NOTICE & ~E_DEPRECATED);

class menu_multi
{

    function showMenu_type_1(){
        // since $pd is global we have to be explicit that's what we want.
        global $pd;
        $pdo = $pd->getConnection();
        $sql_1 = $pdo->query("SELECT * FROM category WHERE menu_parent_id = 0 && type= 'MT01'");
        print_r($sql_1);
        foreach ($sql_1 as $value) {
            print_r($value);
        }
    }
}

$m = new menu_multi;
$m->showMenu_type_1();

我做了这个表来测试：

CREATE TABLE `category` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `menu_parent_id` int(11) DEFAULT NULL,
  `name` varchar(20) DEFAULT NULL,
  `type` varchar(20) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

这是表格中的数据：

INSERT INTO `category` (`id`, `menu_parent_id`, `name`, `type`)
VALUES
    (1, 0, 'item 1', 'MT01'),
    (2, 0, 'item 2', 'MT01'),
    (3, 0, 'item 3', 'MT01'),
    (4, 0, 'item 4', 'MT01'),
    (5, 0, 'item 5', 'MT01');

这是测试的输出：

PDOStatement Object
(
    [queryString] => SELECT * FROM category WHERE menu_parent_id = 0 && type= 'MT01'
)
Array
(
    [id] => 1
    [0] => 1
    [menu_parent_id] => 0
    [1] => 0
    [name] => item 1
    [2] => item 1
    [type] => MT01
    [3] => MT01
)
Array
(
    [id] => 2
    [0] => 2
    [menu_parent_id] => 0
    [1] => 0
    [name] => item 2
    [2] => item 2
    [type] => MT01
    [3] => MT01
)
Array
(
    [id] => 3
    [0] => 3
    [menu_parent_id] => 0
    [1] => 0
    [name] => item 3
    [2] => item 3
    [type] => MT01
    [3] => MT01
)
Array
(
    [id] => 4
    [0] => 4
    [menu_parent_id] => 0
    [1] => 0
    [name] => item 4
    [2] => item 4
    [type] => MT01
    [3] => MT01
)
Array
(
    [id] => 5
    [0] => 5
    [menu_parent_id] => 0
    [1] => 0
    [name] => item 5
    [2] => item 5
    [type] => MT01
    [3] => MT01
)