致命错误:调用成员函数query()PHP CLASS [英] Fatal error: Call to a member function query() PHP CLASS
问题描述
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:
I'm trying to write this class to connect and query my database, but I got this error:
致命错误:在null中调用成员函数query() 第24行的C:\ xxxxxx \ xxxx \ xxxxx \ xxxxxxx \ pages \ config \ class.php
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');
?>
推荐答案
您的方法:
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>";
}
不会从方法中调回$connection，因此rest方法调用失败:
does not retun the $connection back from the method so the rest method calls fail do this:
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，因为对于每个执行的查询，代码都(重新)连接到数据库.这是不必要的昂贵/低效的.
As mentioned, your code is not efficient since for every query performed the code (re-)connects to the DB. THis is unnecessarily expensive/inefficient.
有很多方法可以解决这个问题.
There are many approaches to solve this.
- 在数据库类的实例上连接到数据库
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;
}
}
- 惰性连接，即仅在首次执行查询时进行连接
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>";
}
}
}
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