在类声明中使用外部对象-PHP

Question

So let's say I have two PHP classes : User & Connection .

What they do is obvious from their names.

Now suppose I have this code:

User.php

<?php

class User {

    static function get_email( $user_id ) {
        $conn_object = new Connection();
        $connection  = $conn_object->connection;
        // do stuff with the connection object
    }

}

?>

Connection.php

<?php

class Connection {

    public $connection;

    public function __construct() {
        $this->connection = // connect to the database here
    }

}

?>

main.php

<?php

require "Connection.php";
require "User.php";

$email = User::get_email( 4 ); // this doesn't work

?>

When I do something like that in main.php , I get a bunch of errors. When I var_dump( $conn_object ); in the User.php file, I always get a null , like the file doesn't even "see" the Connection object, or know it exists.

However, when I use the Connection class in main.php directly, I don't get any errors and everything runs smoothly. This means my Connection object doesn't have any syntax errors or otherwise.

Is this kind of thing not allowed to be done in PHP? Does the language not allow the usage of a class in a class?

Answer 1

Remember classes share methods or properties by inheritance or depencency injection.

<?php

class Connection {

    protected $connection;
    //we changed protected because only direct inherit can acces

    public function __construct() {
        $this->connection = // connect to the database here
   }

}

<?php

include connection.php...

class User extends Connection{

      function __construct(){
        parent::contruct();
      }

    static function get_email( $user_id ) {

        $this->connection->yourDbstuff ;
        // do stuff with the connection object
    }

}

?>

Answer 2

FYI: I try to answer a question as if I was asking it for the first time and try to include as much information as would be needed by someone who does not have as much knowledge as you or I. It makes it easier for those just learning to find answers.

require "Connection.php";

require "User.php";

$email = User::get_email( 4 ); // this doesn't work

The '::' references a parent method so if you have not extended the Connection class with the User class, it will not work. And even if you have, it is not guaranteed to work, which more likely means that I did something wrong when trying it.

To use an external connection object, you would need to pass the connection object to the user object so that the user object can use the connection object as follows.

$thisConnection = new Connection(); $thisUser = new User(); $thisUser = new User($thisConnection); or $thisUser->setConnection($thisConnection);

Then within your user class you would need a single method or a group of methods that duplicates the methods within the connection class.

However, as was mentioned by Joaquin Javi, Object Oriented Programming uses inheritance and child objects inherit and have access to parent object methods.

In addition, by extending the connection class with the user class, you save yourself a whole lot of coding.

On the other hand, if you have a specific reason you do not want to use extends and the inheritance shortcut, you will need to pass the Connection object into the User object.

Just to be clear, when you extend the Connection class with the user class, the user class will inherit the methods as well as the variables of the connection class as long as they are set to public or protected, and you will be able to access any variable or method such as the get_email method as follows:

$thisUser->get_email( 4 );

Hope this helps. Scott