Class inside a class

[WhatWhat]

Hi!

 

 

Let's say I have 2 classes: User and Database. I have to use the Database class inside the User class. What's the best way to do this?

 

 

Option #1 - new object

class User
{
    __construct()
    {
        $this->DB = new Database;
    }

    doSomething()
    {
        $this->DB->query("SELECT 1");
    }
}


$DB = new Database;
$User = new User;

$User->doSomething();

 

 

Option #2 - reference

class User
{
    __construct()
    {
        //
    }

    doSomething()
    {
        $this->DB->query("SELECT 1");
    }
}

$DB = new Database;
$User = new User;

$User->DB =& $DB;

$User->doSomething();

 

 

Option #3 - something else?

 

 

What should I do any why?

 

 

Thanks

[Jenk]

Option 3:

<?php

class User
{
    private $_db;

    public function __construct (DB $db)
    {
        $this->_db = $db;
    }

    public function doSomething()
    {
        //do something with $this->_db
    }
}

$user = new User(new DB());

?>

[WhatWhat]

Thanks. 2 questions:

 

1. Why is that better than #1 or #2?

2. What if I want to use X classes in the User class, not just one?

[emehrkay]

I just put together a little set of classes that has a base db class that handles the queries and all of the db interaction and i have classes for each table which contain all of the queries for that table - is that what you're doing?

[utexas_pjm]

1. Why is that better than #1 or #2?

 

Jenk's implementation is better than #1 because you instantiating a DB object every time you instantiate a user a User object.  If the DB object is of size x and you have n instances of the User class you are using n*x space.

 

 

As for #2 It is generally considered bad practice to access member data directly.

 

i.e.,

 

<?php
//..
$User->DB =& $DB;
//..
?>

 

At the very least you should provide a mutator method such that the member data is not accessed directly.

 

i.e.,

 

<?php
//..
$User->setDb($db);
//..
?>

 

However, because the User object is composed of a DB object it makes sense to pass this into the constructor as Jenk did.  It would not make sense to call doSomething() on the User object if $_db was null.  Passing this into the constructor ensures the object is complete before allowing any methods to be called.

 

2. What if I want to use X classes in the User class, not just one?

 

<?php
// ..
class User
{
    private $_db;
    private $_foo;

    public function __construct (DB $db, $foo)
    {
        $this->_db = $db;
        $this->_foo = $foo;
    }

    public function doSomething()
    {
        //do something with $this->_db
    }
}
//...
$user = new User($db, $someOtherInstance);
?>

 

Best,

 

Patrick

[Jenk]

Thanks. 2 questions:

 

1. Why is that better than #1 or #2?

If you want to use a different DB class (but it must have the same interface) it would not be a problem at all, you just provide a different object..

<?php

$user1 = new User(new DB());
$user2 = new User(new OtherDB());

?>

2. What if I want to use X classes in the User class, not just one?

add extra arguments, or extra methods for setting the objects, as shown above by Patrick.

[WhatWhat]

I just put together a little set of classes that has a base db class that handles the queries and all of the db interaction and i have classes for each table which contain all of the queries for that table - is that what you're doing?

 

I have a DB class that handles the queries, User class (user session, login, logout), some other not-so-important classes and classes for each module of the site, for example "News" - I guess that's similar to "classes for each table".

 

 

 

@ Patrick & Jenk

 

Thanks!