Problems connecting to MySQL using PDO

问题

I've been trying to convert my application from using the depreciated mysql syntax to PDO for connecting to the database and performing queries, and it's been a pain so far.

Right now I have a class, db_functions.php, in which I'm trying to create a PDO connection to the database, as well as perform all the CRUD operations inside of.

Here is a sampling of the code:

db_functions.php
<?php

class DB_Functions {

    private $db;

    // constructor
    function __construct() {
        require_once 'config.php';
        // connecting to mysql
        try {
        $this->$db = new PDO('mysql:host=localhost;dbname=gcm', DB_USER, DB_PASSWORD);
        }
        catch (PDOException $e) {
            $output = 'Unable to connect to database server.' .
            $e->getMessage();
            exit();
        }
    }

    // destructor
    function __destruct() {

    }

public function getAllUsers() {
    try {
    $sql = "select * FROM gcm_users";
    //$result = mysql_query("select * FROM gcm_users");
    $result = $this->$db->query($sql);
    return $result;
    }
    catch (PDOException $e) {
        $error = 'Error getting all users: ' . $e->getMessage();
    }
}

With that code, i'm getting the following error:

Notice: Undefined variable: db in C:\xampp\htdocs\gcm\db_functions.php on line 12

Fatal error: Cannot access empty property in C:\xampp\htdocs\gcm\db_functions.php on line 12

Line 12 is:

 $this->$db = new PDO('mysql:host=localhost;dbname=gcm', DB_USER, DB_PASSWORD);

How could I fix this so that I have a proper instance of a PDO connection to my database that I can use to create queries in other methods in db_functions, such as getAllUsers()

I used the answer found at How do I create a connection class with dependency injection and interfaces? to no avail.

回答1:

TYPO

//$this->$db = 
$this->db = 

same here

//$this->$db->query($sql);
$this->db->query($sql);

and i also would use 127.0.0.1 instead of localhost to improve the performance otherwise making a connection will take very long... a couple of seconds just for connection...

来源：https://stackoverflow.com/questions/24253898/problems-connecting-to-mysql-using-pdo