我已经查看了其他问题,大多数人说这与调用静态方法等有关,但没有一个能够解释为什么我会收到此错误?
我已经习惯了类,不想在每个类中构建与数据库的连接,而是为它提供一个类,每个使用数据库连接的类的其他类都使用(从长远来看,它更有意义,工作量更少)。
下面是 2 个类,init.php它们加载类和对索引上的类的调用.php所有这些都是最基本的。
这是我在"报告类"中指出的引发错误的行。
数据库类
<?php
class DB{
public static $instance = null;
private $_pdo;
public function __construct(){
try{
$this->_pdo = new PDO('mysql:host=12345;dbname=12345', '12345', '12345');
$this->_pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}catch(PDOException $e){
$e->getMessage();
}
}
public static function getInstance() {
if(!isset(self::$instance)) {
self::$instance = new DB();
}
return self::$instance;
}
}
?>
报告类
<?php
class Reports{
private $_db;
public function __construct(){
$this->_db = DB::getInstance();
}
public static function getReports($table, $version, $orderBy){
$sql = "SELECT * FROM {$table} WHERE name = :name ORDER BY :orderBy";
$query = $this->_db->prepare($sql); // line thats throwing the error on $this->_db
$query->execute(array(
':name'=>$version,
':orderBy'=>$orderBy
));
$result = $query->fetchALL(PDO::FETCH_OBJ);
return $result;
}
}
?>
初始化.php
<?php
error_reporting(E_ALL);
session_start();
session_regenerate_id(true);
function autoload($class) {
require_once 'classes/' . $class . '.php';
}
spl_autoload_register('autoload');
?>
索引.php
<?php
require_once "core/init.php";
$reports = Reports::getReports("demo", "name1", "id");
echo "<pre>" . print_r($reports) . "</pre>";
?>
是什么原因造成的?
它是一个
静态方法,因此您需要静态访问它或获取该方法所在的实例。按照您目前设计的方式,没有办法做到这一点。无论如何,该方法似乎不应该是静态的,所以我只会让它成为非静态的:
class Reports{
private $_db;
public function __construct(){
$this->_db = DB::getInstance();
}
public function getReports($table, $version, $orderBy){
$sql = "SELECT * FROM {$table} WHERE name = :name ORDER BY :orderBy";
$query = $this->_db->prepare($sql); // line thats throwing the error on $this->_db
$query->execute(array(
':name'=>$version,
':orderBy'=>$orderBy
));
$result = $query->fetchALL(PDO::FETCH_OBJ);
return $result;
}
}
用法:
require_once "core/init.php";
$report = new Reports();
$reports = $report->getReports("demo", "name1", "id");
echo "<pre>" . print_r($reports) . "</pre>";
如果您设置为保持静态,那么您getReports
方法将需要执行以下操作:
public static function getReports($table, $version, $orderBy){
$reports = new self();
$sql = "SELECT * FROM {$table} WHERE name = :name ORDER BY :orderBy";
$query = $reports->_db->prepare($sql); // line thats throwing the error on $this->_db
$query->execute(array(
':name'=>$version,
':orderBy'=>$orderBy
));
$result = $query->fetchALL(PDO::FETCH_OBJ);
return $result;
}
将报告类更改为:
class Reports{
public static function getReports($table, $version, $orderBy){
$db = DB::getInstance();
$sql = "SELECT * FROM {$table} WHERE name = :name ORDER BY :orderBy";
$query = $db->prepare($sql);
$query->execute(array(
':name'=>$version,
':orderBy'=>$orderBy
));
$result = $query->fetchALL(PDO::FETCH_OBJ);
return $result;
}
}