Principle of Chain Operation Implementation in PHP

In a class, if there are multiple methods, when you instantiate this class and call the method, you can only call them one by one, similar to:

db.php

<?php
class db
{
public function where()
{
//code here
}
public function order()
{
//code here
}
public function limit()
{
//code here
}
} 

index.php

<?php
$db = new db();
$db->where();
$db->order();
$db->limit(); 

If you want to implement chain calls, you need to add return $this at the end of the method.

db.php

<?php
class db
{
public function where()
{
//code here
return $this;
}
public function order()
{
//code here
return $this;
}
public function limit()
{
//code here
return $this;
}
} 

index.php

<?php
$db = new db();
$db->where();->order();->limit();

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