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Cover image for Getting started with Slim PHP framework by building a very simple MVC/OOP app

Getting started with Slim PHP framework by building a very simple MVC/OOP app

charliedevelops profile image charliedeveloper ・4 min read

Aim:
We are going to build a Slim application that creates a farm pen and outputs the noises that the cow & chicken inside the pen make.

Requirements:
- A pen can only contain a cow and a chicken (will help us practice with slim dependancy injection container)
- Must implement an MVC approach (help us understand how models, views and controllers work together)

1. So we are gonna need the slim skeleton application - open your command line and run:

composer create-project slim/slim-skeleton slimFarm

  • if you don’t have composer installed globally use the composer documentation to get it

2. On your command line navigate (cd) into slimFarm directory that has been made for you

3. We are going to run a php server so we can see that the slim app is present and working

  • In your command line run: php -S 0.0.0.0:8080 -t ./public/

4. Go to http://0.0.0.0:8080/ to check its working (you should get the slim default page)

5. Open files in your text editor and make a Classes folder inside src

6. Add your namespace to autoloading in composer.json:

"autoload": {
  "psr-4": {
    "Farm\\": "src/classes/"
  }
},
  • n.b: this is in addition to the already existing autoload-dev

  • This will mean we can reference our classes using namespaces rather than having loads of require's everywhere.

7. Open a new tab in your command line and run composer dump-autoload in the command line

  • This regenerates our autoloading and namespaces to contain the changes we just made in step 6.

8. We need our Cow and Chickens to go in the pen! so make our classes inside Classes/Models folder:

namespace Farm\Models;

class ChickenModel
{
    public $speak = 'cluck';
}
namespace Farm\Models;

class CowModel
{
    public $speak = 'moo';
}

9. Create a Pen class inside Classes/Models folder:
namespace Farm\Models;

class PenModel
{
    public $cow;
    public $chicken;

    public function __construct($cow, $chicken)
    {
        $this->cow = $cow;
        $this->chicken = $chicken;
    }

    public function getCowNoise(){
        return $this->cow->speak;
    }

    public function getChickenNoise(){
        return $this->chicken->speak;
    }
}

10. Lets make a factory so that Pen can be created quickly with its dependencies in just one call.

  • Make a Factories folder (inside the Classes folder)
  • Make PenModelFactory:
namespace Farm\Factories;

class PenModelFactory
{
    function __invoke()
    {
        $cow = new \Farm\Models\CowModel();
        $chicken = new \Farm\Models\ChickenModel();
        return new \Farm\Models\PenModel($cow, $chicken);
    }
}
  • Our factory doesn't need a constructor function, the logic is put inside the __invoke magic method because of the way it is called from our Dependency Injection Container (DIC)

11. So now we have made our factory let's put it in our DIC

  • Think of the DIC as a big associative array that knows how to instantiate objects for you we put in there for use later in our application
  • Open up src/dependancies.php
  • There are preexisting things inside the DIC already
  • Add our factory like this:
$container['penModel'] = new \Farm\Factories\PenModelFactory();
  • We are saying "inside our container (DIC) add a new key of 'penModel' and when we ask for that 'penModel' run our factory to instantiate and return a ready made pen object with all the dependencies (cow + chicken) taken care of."

12. Let’s look in our routing file to see how we deal with different HTTP Requests to our application.

  • Like the defaults already written in here we could use quick anonymous functions to save having to create a factory but we instead are gonna "do it right" so we will make a route and use a controller to call our business logic.
  • Delete the existing $app->get(.....) routes already in the file (we will create our own)
  • Set up our route:
$app->get('/makeMeAPen', <where our callback will go> );
  • /makeMeAPen is the URL extension people are expecting to visit to run our code
  • But we don't have a controller yet so....

13. Let’s make a controller to call our PenFactory and render out a view:

  • Create a Controllers directory inside src/Classes
  • Create PenController inside src/Classes/Controllers/
namespace Farm\Controllers;

class PenController
{
    protected $container;

    //this constructor passes the DIC in so we can get our PenFactory out of it later
    function __construct($container)
    {
        $this->container = $container;
    }

    function __invoke($request, $response, $args)
    {
        //create our pen from Penfactory in DIC
        $pen = $this->container->get('penModel');

        //assign args (variables that will be available on rendered view)
        $args['cowNoise'] = $pen->getCowNoise();
        $args['chickenNoise'] = $pen->getChickenNoise();

        //get the default template renderer out of DIC and pass the response and $args to a template file
        return $this->container->get('renderer')->render($response, 'showFarm.phtml', $args);
    }
}

14. Now our controller exists lets add it in as the thing that happens when our route is hit:

$app->get('/makeMeAPen', \Farm\Controllers\PenController::class);

15. Notice in our PenController we are calling a template file that doesn't exist yet so lets create it:

  • Create showFarm.phtml in /templates folder
  • Use the values you put into the $args associative array as normal variables:
<!DOCTYPE html>
<html>
    <head>
        <title>slimFarm</title>
        <style>
            h2 {
                font-size: 10rem;
                color: red;
            }
        </style>
    </head>
    <body>
            <h2>Cows go: <?php echo htmlspecialchars($cowNoise); ?>!</h2>
            <h2>Chickens go: <?php echo htmlspecialchars($chickenNoise); ?>!</h2>
    </body>
</html>

16. Navigate to http://0.0.0.0:8080/makeMeAPen and behold the brilliance of your super advanced app!

Posted on by:

charliedevelops profile

charliedeveloper

@charliedevelops

A fullstack developer and coding trainer based in the South West, UK

Discussion

markdown guide
 

Lovely! What I like most about this tutorial is that it goes beyond the one-page code mentality that Slim applications seem to be stuck in, and demonstrates how to add structure. Good job! :-)

 

Thanks! Really pleased you liked it!

 

I have the error message "Entry \"Farm\\Controllers\\PenController\" cannot be resolved: Parameter $container of __construct() has no value defined or guessable\nFull definition:\nObject (\n class = Farm\\Controllers\\PenController\n lazy = false\n __construct(\n $container = #UNDEFINED#\n )\n)" and think it might be due to this: "In contrast with Slim 2 and Slim 3, Slim 4 does not ship with a DI container, but instead, supports any PSR-11 compatibly DI container that you provide." (akrabat.com/dependency-injection-i...)

But since I am a total noob it could also be another problem. :)

 

The problem was, that the parameter that gets passed to the constructor is tested for its type by slim. So we have to type-hint it now with "Container". But this is just one of the problems this tutorial raises when applied to Slim 4.

 

Getting the following error:

{
"statusCode": 500,
"error": {
"type": "SERVER_ERROR",
"description": "Call to undefined method Farm\Factories\PenModelFactory::getCowNoise()"
}
}

 

I like this tutorial very much for getting a basic grasp on what is going on. But there is no src/dependencies.php (also no dependAncies.php). Is this due to a new version of slim? How can we proceed anyway? Thanks a lot!

EDIT: I tried it anyway (creating a depandencies.php and putting in that single line) and got the following error that I do not understand since this file exists: Uncaught Error: Class 'App\Application\Handlers\HttpErrorHandler

 

Great article Charlie!..
I found this article very useful to understand the slim with a custom mvc dependency!
Question: - How would you update the steps 11, 13 and 14 for a Slim4 skeleton?..
Thank You! :-)