oop structure for make class such as PDO class structure - php

Question

How to make class structure like PDO or ORM
$query = DB::table('users')->select('name');
$users = $query->addSelect('age')->get();
OR
$stmt = $pdo->prepare($sql);
$stmt->bindvalue(':u',intval($_SESSION['userId']),PDO::PARAM_INT);
$stmt->execute();
What is returned in to $query or $stmt?
how to design class structure like them?
Thank you
EDIT
$query = DB::table('users')->select('name');
meaning :
function select(){
//
return $this;
}
what's returned in to $query for this structure :
$query->addSelect('age')->get();

Answer 1

PDO is done by returning a new class (PDOStatement) with its own methods (read more about it), but it would be the same as:
<?php
class ClassOne
{
private $connection;
public function __construct($database_stuff)
{
$this->connection = $database_stuff;
}
public function prepare($sql)
{
// Code that does something with the $sql
// Then return a new class
return new ClassTwo($this);
}
}
class ClassTwo
{
private $ClassOne;
public function __construct(ClassOne $Class)
{
$this->ClassOne = $Class;
}
public function execute()
{
// Code that does something with ClassOne
}
}
# Start that initial class
$Class = new ClassOne('database:type;host=example;etc=yadayada');
# Do class one method
$query = $Class->prepare("SELECT * FROM fake_table");
# $query is now ClassTwo, so you do method from ClassTwo
$query->execute();
The ability to chain methods together is achieved because the current method returns the object back in the form of $this:
<?php
class DBClass
{
protected $connection,
$value;
public function __construct($connection)
{
$this->connection = $connection;
}
public function prepare($value)
{
$this->value = $value;
# Return the object
return $this;
}
public function execute()
{
echo $this->value;
# Return the object
return $this;
}
}
$con = new DBClass("login creds");
$con->prepare("update stuff if stuff = 'things'")->execute();
?>