PHP db connection issue with multiple files

Dev Zone Code
1

Having a problem making connection to a database in File #2. Code is below.

File #1

<?php

require_once 'login.php';
require_once 'file2.php';

     $db_database = '00044736';

     $connection = new mysqli($db_hostname, $db_username, $db_password, $db_database);
	
     $myObj = new A();
	
     $myObj->qConnect('00044736');

?>

File #2

<?php 
                   
     class A {
        
          public function qConnect($var1) {
        			
          $db_database = $var1;
        
          $connection = new mysqli($db_hostname, $db_username, $db_password, $db_database);
 
          } 

     }
        
?>

Below are the errors I receive when running File #1; I'm unable to make a connection in File #2. Any ideas?

Notice: Undefined variable: db_hostname
Notice: Undefined variable: db_username
Notice: Undefined variable: db_password

2

The variables are not in scope in class A. You need to add global $db_hostname, $db_username, $db_password, $db_database; inside your function definition. So:

    <?php
require_once 'login.php';
class A
{
    public function qConnect($var1)
    {
        global $db_hostname, $db_username, $db_password, $db_database;

        $db_database = $var1;

        $connection = new mysqli($db_hostname, $db_username, $db_password, $db_database);
    }
}
1 Like
3

Yep. That was it. Thanks.

4

Any time.

5

captainwillard, I'd like to pose another question to you. In Java, you can declare field attributes (instance variables). For example

public class foo {

    public int myVariable = 200;

         public void bar() {

              System.out.print(myVariable); // outputs 200
         }

}

In the example above you will be able to use (and reuse) the variable 'myVarialbe' for any method(s) within class foo.

If I understand correctly, in PHP you can declare a variable wherever you want, but then if you want to use it in a class with 10 functions you would have to re-declare your variable as global in each function within the class. For example

<?php

	$zen = 55;
	
	foo();
	bar();
	
	function foo() {
		
		global $zen;
		
		echo $zen;
		
	}
	
	
	function bar() {
		
		global $zen;
		
		echo $zen;
	}

?>

Is there a better way to do this because it just seems redundant.

6

You can actually write OO PHP in a very java-like way. Check out http://php.net/manual/en/language.oop5.php

So your PHP class would look like this:

<?php
class FooBar
{
    private $zen = 55;

    function foo()
    {
        echo $this->zen;
    }

    function bar()
    {
        echo $this->zen;
    }
}

$myFooBar = new FooBar();

$myFooBar->foo();
$myFooBar->bar();
7

DO NOT use globals. This is entirely the wrong solution to your issue, and will only make things more difficult in the long run. Globals make code harder to understand, debug, maintain, and modify.

Instead, use Dependency Injection:

<?php

// define your connection details.
$db_hostname = "mysql hostname";
$db_username = "mysql username";
$db_password = "mysql password";
$db_database = '00044736';

// create your connection
$connection = new mysqli($db_hostname, $db_username, $db_password, $db_database);

// GIVE the connection to the object that needs it.
// this is Dependency Injection.  That's all there is to it.
$myObj = new A( $connection );

//  rest of your code

In your class A, you will assign the connection to a property, where it will be available to any class method which needs to use it.

→ more about Dependency Injection and why it is good
→ PHP The Right Way

1 Like
8

Ahh, definitely more in my comfort zone. Thanks.

Thanks traq2, I will look into this.