PHP5 Method Chaining

Salathe · 09-18-2007, 01:14 PM

Introduction
In this article, I'll be talking about a useful new feature introduced in PHP5 as part of the OOP improvements over PHP4. This feature is called Method Chaining and enables us to do pretty cool things like:

PHP Code:


			
$object->method_a()->method_b()->method_c();

So really what's this all about? Well, one change (of many) between PHP4 and PHP5 is that now methods can return objects. That's only a small change but allows for a new way of thinking about how you handle objects and their methods.

In order to be able to chain methods together, as mentioned earlier, you need to be able to return an object. The returned object does not necessarily need be the same one from which the method is being called, but we'll not be touching on that fact in this article. Let's go for a quick illustration of how to put all of this into action.

Regular Use of a Class
We'll start off with a basic class, which doesn't do anything particularly interesting but it will serve our purpose.

PHP Code:


			
// This Person class encapsulates a couple of properties which
// a person might have: their name and age.
// We also give the Person the opportunity to introduce themselves.
class Person
{
    private $m_szName;
    private $m_iAge;
    
    public function setName($szName)
    {
        $this->m_szName = $szName;
    }
    
    public function setAge($iAge)
    {
        $this->m_iAge = $iAge;
    }
    
    public function introduce()
    {
        printf(
            'Hello my name is %s and I am %d years old.',
            $this->m_szName,
            $this->m_iAge);
    }
}

Now, we can create a new Person (see example below) and give them a name and age. Using the introduce method, the person can them introduce themselves.

PHP Code:


			
// We'll be creating me, digitally.
$peter = new Person();

// Let's set some attributes and let me introduce myself.
$peter->setName('Peter');
$peter->setAge(23);
$peter->introduce();

The above example would output:

Hello my name is Peter and I am 23 years old.

Implementing Method Chaining
Great, but you already knew how to do that didn't you! In actuality, we only need to add two lines of code to the basic class above to enable us to write a chain, and the second line is a repeat of the first! How's it done? Quite simply we need to return the Person object from each method. At the moment, none of the methods actually return anything so we'll amend that now. We just need to add return $this; to the methods setName and setAge.

The amended Person class is as follows:

PHP Code:


			
// This Person class encapsulates a couple of properties which
// a person might have: their name and age.
// We also give the Person the opportunity to introduce themselves.
class Person
{
    private $m_szName;
    private $m_iAge;
    
    public function setName($szName)
    {
        $this->m_szName = $szName;
        return $this; // We now return $this (the Person)
    }
    
    public function setAge($iAge)
    {
        $this->m_iAge = $iAge;
        return $this; // Again, return our Person
    }
    
    public function introduce()
    {
        printf(
            'Hello my name is %s and I am %d years old.',
            $this->m_szName,
            $this->m_iAge);
    }
}

Ok, is that it? Yep, really. Because we return the Person from those methods, it enables us to group method calls together in a sequence, or chain. I'll re-do the previous example but this time using our new magical chaining abilities.

PHP Code:


			
// We'll be creating me, digitally.
$peter = new Person();

// Let's set some attributes and let me introduce myself, 
// all in one line of code.
$peter->setName('Peter')->setAge(23)->introduce();

That example will produce exactly the same output as our regular, boring example earlier! All because we return the Person object in the setName/Age methods.

How does that work?
If you're a bit confused about precisely what is going on here, let me try to walk you through the process, step by step. We'll go through the line of code as it is processed, from left to right.

First up is $peter->setName('Peter'). This assigns the person's name to be Peter, my name and returns $this -- that is, the $peter object. So at the moment Peter has his name, but no age!

Next up comes ->setAge(23). Because we're chained with the previous method, PHP interprets the code and says "execute the setAge method belonging to whatever was returned from the previous method." In this case, PHP executes the setAge method belonging to our Person object, $peter.

The exact same thing happens when we finally call the introduce method. PHP executes the introduce method belonging to whatever was returned from the setAge method call: $peter.

Hopefully, that's at least a bit clear and I'll let you mull over this confusing (until you get it) subject for a while. I'll leave you with the note that because we can chain methods, they can be called more than once and in whatever order we like which could lead to the amazingly useless snippet below:

PHP Code:


			
// Hello my name is Winifred and I am 72 years old.
$peter->setAge(23)
      ->setName('Peter')
      ->setName('Winifred')
      ->setAge(72)
      ->introduce();

In Conclusion
We can boil this whole article down into one short sentence. If you return $this then you can chain the method calls together. Done. :)

Tanax · 10-01-2007, 11:06 AM

And this would be useful because..? :P

Karl · 10-01-2007, 11:24 AM

Readability and reduction of code repeation. Consider the following example I use in my library:

PHP Code:


			
$aMembers = $this->m_pMembers
                    ->join('jobs')
                    ->join('orders')
                    ->fetchAll($szFields, $szConditions);

The same code could be written like this, without method chaining:

PHP Code:


			
$this->m_pMembers->join('jobs');
$this->m_pMembers->join('orders');
$aMembers = $this->m_pMembers->fetchAll($szFields, $szConditions);

Admitidly, we've actually added an extra line of code using method chiaining, but we've reduced the amount of code written, removed duplicate code and made it much easier to read. It's all a matter of preference in all honesty, there is no clear cut advantage (that I personally know of, can anyone give me one?) of using method chaining, it's simply a OOP feature that can be used to help improve your code.

Acrylic · 10-23-2007, 11:25 AM

Wow! Thanks for this it will come in handy. :)

dschreck · 11-13-2007, 06:56 PM

good write up, needed to explain this to some JR's, googled it, and found this here. Good job explaining this very usable and convenient pattern.

so, kudos for you.

Morishani · 11-15-2007, 12:13 PM

Thanks! Very useful :)

gilbertoalbino · 10-28-2008, 02:55 PM

Hum, pretty good! I was just thinking about it and found that this is very great a progress to PHP language, because, as you must know most languages, both scripting or not have method chaining somehow, to webdevelopers it would be pretty nice for PHP allow method chaining, in fact we generally deal with Javascript often, and as you know too, string.value.length is now possible in php as string()->value()->length().
Great post, thanks again!

exquisiteoath · 11-28-2008, 02:07 AM

I've been writing chaining in JavaScript with exactly this same approach for close to a year new, wishing that PHP could offer the same functionality.

Then it occurs to me... hey, I never googled it. I google it, and this is the first thing I find.

I had completely missed that we can now return objects. That changes everything.

Wildhoney · 11-28-2008, 02:25 AM

Lol

Such a good find, I imagine! Welcome to the community as well, my friend!

zxt3st · 11-28-2008, 05:17 AM

well, as i study some of the articles regarding classes, i have read about this technique wherein you return the object so that you can do the chain.

e.g
the object is the cat then we apply some color on it. Yellow after which return the object again, so we can again apply any other property on it.

Cat(object)->yellow(color)->Cat(returned object)->etc..

so any instances if we apply it to classes we can do the chain as what discuss above.(if im not mistaken about it)

PHP Code:


			
$obj = new object();
$obj->setname(params)->setcolor(params)->setsize(params)->etc..

Thanks for the share, atleast we also have a detail discussion about it too :)

gilbertoalbino · 11-28-2008, 12:38 PM

Quote:

Originally Posted by exquisiteoath

I've been writing chaining in JavaScript....

Sure! This is fantastic!

Jarod B · 12-20-2009, 03:26 AM

Isn't there like a way where you can use these both separate? , I tried these:

...*removed*
Okay I made a little solution for the selecting weather to chain your class or not, it's fussy though, but it helps I guess

:

PHP Code:


			
<?php
// December 19 2009 [10:02 a.m. MS]

class person {
    private $name;
    private $age;
    private $chain; // want to chain? false (/no) by default
    
    function __construct($chain=false) {
        $this->chain = $chain;
        
        if($this->chain == false) { // Set to false by default
            return false;
        } else {
            return true;
        }
    }
    
    public function set_name($name) {
        if($this->chain == false) {
            return $this->name = $name;
        } else {
            $this->name = $name;
            return $this;
        }
    }
    
    public function set_age($age) {
        if($this->chain == false) {
            return $this->age = $age;
        } else {
            $this->age = $age;
            return $this;
        }
    }
    
    public function introduce() {
        if(empty($this->name)) {
            print("I need a name!");
        } else if(empty($this->age)) {
            print("I dont have an age!");
        } else {
            printf("Hello there, my name is <b>%s</b> and I am <b>%s</b> years old.", $this->name, $this->age);
        }
    }
}

    $person = new person();
    
    $name = "Jarod";
    $age = 17;
    
    echo "Normal Method";
    echo "<br />";
    echo $person->set_name($name) . "<br />";
    echo $person->set_age($age) . "<br />";
    $person->introduce();
    echo "<br />";
    echo "<br />";
    echo "<br />";
    echo "Chaining Method";
    echo "<br />";
    
    $person = new person(true); // chaining method
    $person->set_name($name)->set_age($age)->introduce();

/** OUTPUT::>>
* Normal Method
* Jarod
* 17
* Hello there, my name is Jarod and I am 17 years old.
* 
* 
* Chaining Method
* Hello there, my name is Jarod and I am 17 years old.
*/
?>

Salathe · 12-20-2009, 11:54 AM

Hi Jarod, a better option (in my opinion) would be to make use of the class hierarchy rather than doing everything in one class.

E.g. (just snippets)

PHP Code:


			
class Person {

    protected $name;

    public function set_name($name) {

        return $this->name = $name;

    }

}



class ChainablePerson extends Person {

    public function set_name($name) {

        parent::set_name($name);

        return $this;

    }

}

Jarod B · 12-20-2009, 11:15 PM

I guess, but they seem to be the same way to me if you think about it, just in another class

.

Killswitch · 12-24-2009, 06:54 AM

Awesome. I recently learned of method chaining by playing with Kohana and thought you needed to do this with factory. Continuing to learn... it's nice :D

Jarod B · 12-24-2009, 11:04 PM

Can you explain to be what Kohana your talking about (I dont know either really)? lol

Killswitch · 12-25-2009, 06:38 AM

Quote:

Originally Posted by Jarod B

Can you explain to be what Kohana your talking about (I dont know either really)? lol

Kohana is a framework, see kohanaphp.com.

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lennondevid · 11-01-2012, 07:08 AM

Quote:

Originally Posted by Salathe

Introduction
In this article, I'll be talking about a useful new feature introduced in PHP5 as part of the OOP improvements over PHP4. This feature is called Method Chaining and enables us to do pretty cool things like:

PHP Code:


			
$object->method_a()->method_b()->method_c();

So really what's this all about? Well, one change (of many) between PHP4 and PHP5 is that now methods can return objects. That's only a small change but allows for a new way of thinking about how you handle objects and their methods.

In order to be able to chain methods together, as mentioned earlier, you need to be able to return an object. The returned object does not necessarily need be the same one from which the method is being called, but we'll not be touching on that fact in this article. Let's go for a quick illustration of how to put all of this into action.

Regular Use of a Class
We'll start off with a basic class, which doesn't do anything particularly interesting but it will serve our purpose.

PHP Code:


			
// This Person class encapsulates a couple of properties which
// a person might have: their name and age.
// We also give the Person the opportunity to introduce themselves.
class Person
{
    private $m_szName;
    private $m_iAge;
    
    public function setName($szName)
    {
        $this->m_szName = $szName;
    }
    
    public function setAge($iAge)
    {
        $this->m_iAge = $iAge;
    }
    
    public function introduce()
    {
        printf(
            'Hello my name is %s and I am %d years old.',
            $this->m_szName,
            $this->m_iAge);
    }
}

Now, we can create a new Person (see example below) and give them a name and age. Using the introduce method, the person can them introduce themselves.

PHP Code:


			
// We'll be creating me, digitally.
$peter = new Person();

// Let's set some attributes and let me introduce myself.
$peter->setName('Peter');
$peter->setAge(23);
$peter->introduce();

The above example would output:

Hello my name is Peter and I am 23 years old.

Implementing Method Chaining
Great, but you already knew how to do that didn't you! In actuality, we only need to add two lines of code to the basic class above to enable us to write a chain, and the second line is a repeat of the first! How's it done? Quite simply we need to return the Person object from each method. At the moment, none of the methods actually return anything so we'll amend that now. We just need to add return $this; to the methods setName and setAge.

The amended Person class is as follows:

PHP Code:


			
// This Person class encapsulates a couple of properties which
// a person might have: their name and age.
// We also give the Person the opportunity to introduce themselves.
class Person
{
    private $m_szName;
    private $m_iAge;
    
    public function setName($szName)
    {
        $this->m_szName = $szName;
        return $this; // We now return $this (the Person)
    }
    
    public function setAge($iAge)
    {
        $this->m_iAge = $iAge;
        return $this; // Again, return our Person
    }
    
    public function introduce()
    {
        printf(
            'Hello my name is %s and I am %d years old.',
            $this->m_szName,
            $this->m_iAge);
    }
}

Ok, is that it? Yep, really. Because we return the Person from those methods, it enables us to group method calls together in a sequence, or chain. I'll re-do the previous example but this time using our new magical chaining abilities.

PHP Code:


			
// We'll be creating me, digitally.
$peter = new Person();

// Let's set some attributes and let me introduce myself, 
// all in one line of code.
$peter->setName('Peter')->setAge(23)->introduce();

That example will produce exactly the same output as our regular, boring example earlier! All because we return the Person object in the setName/Age methods.

How does that work?
If you're a bit confused about precisely what is going on here, let me try to walk you through the process, step by step. We'll go through the line of code as it is processed, from left to right.

First up is $peter->setName('Peter'). This assigns the person's name to be Peter, my name and returns $this -- that is, the $peter object. So at the moment Peter has his name, but no age!

Next up comes ->setAge(23). Because we're chained with the previous method, PHP interprets the code and says "execute the setAge method belonging to whatever was returned from the previous method." In this case, PHP executes the setAge method belonging to our Person object, $peter.

The exact same thing happens when we finally call the introduce method. PHP executes the introduce method belonging to whatever was returned from the setAge method call: $peter.

Hopefully, that's at least a bit clear and I'll let you mull over this confusing (until you get it) subject for a while. I'll leave you with the note that because we can chain methods, they can be called more than once and in whatever order we like which could lead to the amazingly useless snippet below:

PHP Code:


			
// Hello my name is Winifred and I am 72 years old.
$peter->setAge(23)
      ->setName('Peter')
      ->setName('Winifred')
      ->setAge(72)
      ->introduce();

In Conclusion
We can boil this whole article down into one short sentence. If you return $this then you can chain the method calls together. Done. :)

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