how to pass the open database connection to every function in php

Question

I have a separate config file to set db parameters.

<?php
define("DB_HOST", "localhost");
define("DB_USER", "root");
define("DB_PASS", "");
define("DB_NAME", "aa");
?>

And when user entered the user name and password, I open the database connection and validate the user in a another php file.

<?php
include("config.php");
include("database.php");
$dbo = database::getInstance();
$result=$dbo->connect(DB_HOST,DB_USER,DB_PASS,DB_NAME);
if($result){
$un = $_POST['username'];
$pw=$_POST['password'];
$dbo->validte_User_Login($un,$pw);
}
else
print "false";?>

Next I want to do some manipulations in database in another php file. Here how can I geet the already open database connection again without including the config file and calling connect method by passing parameters again?

My database connection function is as below.

function connect($host, $user, $pass, $dbName)
 {
$this->host = $host;
$this->user = $user;
$this->pass = $pass;
$this->dbName = $dbName;

$db_handle = mysql_connect($this->host, $this->user,$this->pass);
$db_found = mysql_select_db($this->dbName, $db_handle);

if ($db_found) {
print "Database Found<br/>";
return true;                                 
}
else
print "Database  not Found<br/>";
return false;
}

Return the $db_handle inside your connect() function. For other functions that require a database handle, you can call the connect() function inside it. — Amal
– Amal, Commented Feb 23, 2014 at 13:40
I have used database::getInstance(). Then it gives INSERT command denied to user ''@'localhost' for table 'user_login' error. only Once I open the connection it gives the results. — kkk
– kkk, Commented Feb 23, 2014 at 13:55

kero · Accepted Answer · 2014-02-23 15:02:21Z

I think there are currently 2 flaws in your code:

Don't use mysql_* functions in new code - they are deprecated. See this answer for more information.
You have a mix of functional and object oriented code. When working with the database, calling ::getInstance() implies that I get a working instance - how should an outstander know, if it was already connected or not and more importantly why should he care.

Both can be solved quite quickly, lets take a look at this getInstance() method:

class database {

    private $instance = NULL;

    public static function getInstance() {
        if (self::$instance === NULL) {
            include 'config.php';
            self::$instance = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
        }

        return self::$instance;
    }

    //etc.

}

Now you can have code like this anywhere in your code

$db = database::getInstance();
$result = $db->query("...");
while ($row = $result->fetch_array()) {

}

because the instance will already be connected and if you have multiple calls to getInstance() it will connect only once.

Of course this shows only a snippet which can be improved at some points, e.g. when loading the db data or handling errors.

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