I have a project am willing to create its files structured like this:
js
css
images
core
--- dblayer.class.php
--- user.class.php
--- comments.class.php
--- etc.class.php
index.php
users.php
The DBLayer class inherits from PDO like this:
class DBLayer extends PDO
{
public function __construct()
{
$options = array(
PDO::ATTR_PERSISTENT => true,
PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
);
$dsn = DB_DRIVER . ":host=" . DB_HOST . ";dbname=" . DB_NAME;
parent::__construct($dsn, DB_USER, DB_PASSWORD, $options);
}
public function getLastId()
{
}
public function getLastError()
{
}
// Other general methods used frequently by other classes
}
The other classes will inherit from DBLayer class:
class User extends DBLayer
{
}
So, my question here: is this good practice in the term of performance, code reuse/ readability(the project may invite other developers in the future)?
In general, no.
Inheritance is for IS-A relationships. You should inherit when you want all the methods of a class to be usable by its extended class.
Do you want calling code to be able to do this:
$user = new User('mysql:host=localhost;dbname=test', $user, $password);
$stmt = $user->query("SELECT * FROM Comments");
In other words, by giving access to general-purpose methods like query(), you allow someone to use the User object to query any unrelated data. That would be very confusing!
As @zerkms says in a comment, "User is not a database [connection]". That is what would be implied by User IS-A PDO.
This is a case where you should favor composition over inheritance. Each of your domain model classes, should HAS-A PDO object, which would give you an opportunity to avoid repeating code in every class.
Your usage would therefore be:
$pdo = new PDO(...);
$user = new User($pdo);