Commonly, in a lot of frameworks, you can find examples of creating a query using the query builder. Often you will see:
$query->select('field');
$query->from('entity');
However, in some frameworks you can also do it like this
$object->select('field')
->from('table')
->where( new Object_Evaluate('x') )
->limit(1)
->order('x', 'ASC');
How do you actually do this kinds of chains?
This is called Fluent Interface -- there is an example in PHP on that page.
The basic idea is that each method (that you want to be able to chain) of the class has to return $this -- which makes possible to call other methods of that same class on the returned $this.
And, of course, each method has access to the properties of the current instance of the class -- which means each method can "add some information" to the current instance.
$this, they can be called "in a typical way".
$this? Can't it return $that and continue from there?
Basically, you have to make every method in the class return the instance:
<?php
class Object_Evaluate{
private $x;
public function __construct($x){
$this->x = $x;
}
public function __toString(){
return 'condition is ' . $this->x;
}
}
class Foo{
public function select($what){
echo "I'm selecting $what\n";
return $this;
}
public function from($where){
echo "From $where\n";
return $this;
}
public function where($condition){
echo "Where $condition\n";
return $this;
}
public function limit($condition){
echo "Limited by $condition\n";
return $this;
}
public function order($order){
echo "Order by $order\n";
return $this;
}
}
$object = new Foo;
$object->select('something')
->from('table')
->where( new Object_Evaluate('x') )
->limit(1)
->order('x');
?>
This is often used as pure eye candy but I suppose it has its valid usages as well.
$setup = $Object->add_component($component_property)->configure($component_properties); Where Object::add_component() returns the Component object it added as a property of $Object (eg. to an array), and it is configured with the Component::configure() method. Without chaining, we would have to determine that last element added to the $Object->Components array, then get the Component object that way.
return $this, does it?class c
{
function select(...)
{
...
return $this;
}
function from(...)
{
...
return $this;
}
...
}
$object = new c;
