Magento 2 has been released! This entire series has been updated to reflect the changes since I originally wrote this post. I install Magento 2 using Composer, I recommend you do to! Learn how to here

If you're here, then you are going to be just excited as I am about creating a full blown Magento 2 module from scratch! This part of the series I'll be covering how to setup your module so that it can be installed via Composer.

To install a module via Composer we'll need to set it up as a public version controlled repository and submit it to packagist.org. I'll walk you through how your composer.json should look, anything else is best left to the composer documentation.

I'll be assuming you have already setup a basic repository, and you are familiar with the CLI.

Module structure

Let's setup our basic module structure now:

    etc/module.xml
    registration.php

In the root directory we'll want to create a composer.json file. And it should look something like this:

    {
        "name": "ashsmith/magento2-blog",
        "description": "A simple blog module.",
        "type": "magento2-module",
        "version": "1.0.0",
        "license": [
            "OSL-3.0",
            "AFL-3.0"
        ],
        "require": {
            "php": "~5.5.0|~5.6.0",
            "magento/magento-composer-installer": "*"
        },
        "extra": {
            "map": [
                [
                    "*",
                    "Ashsmith/Blog"
                ]
            ]
        }
    }

There are only a few elements to this I want to explain, as some of it may be unfamiliar to you.

    "type": "magento2-module"

This defines our repo as a magento2-module, this is so when someone includes your module as a dependency on their Magento 2 install, composer will know what to do with it! And that brings us to the next bit

    "extra": {
        "map": [
            [
                "*",
                "Ashsmith/Blog"
            ]
        ]
    }

What this does is creates a map which will tell Composer how to install this module.

That is: everything (*) should go into the folder: Ashsmith/Blog. Which would mean our module will be installed to: app/code/Ashsmith/Blog.

If you want to learn more about this, head to Alan Kent's blog! This is a fantastic post covering Magento 2 & composer

The first file you'll want to create is the etc/module.xml.

    <?xml version="1.0"?>
    <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
        <module name="Ashsmith_Blog" setup_version="1.0.0" />
    </config>

Noticed the Schema location is a little strange looking? Your IDE won't recongise that, but you can fix that! Here how in PHPStorm: XML Schema Resolution in PHPStorm

Next up, we need a registration.php file in the root of our module. This is picked up by the Magento framework and will handle registering your module with Magento.

<?php
\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'Ashsmith_Blog',
    __DIR__
);

Now, with this done our module has is setup, but it won't work within Magento just yet. We will need to enable it, then upgrade the database too. Like so:

    bin/magento module:status # this will give us the status of each module. It'll show ours as disabled.
    bin/magento module:enable Ashsmith_Blog # this will enable our module
    bin/magento setup:upgrade # upgrade the system, essentially this will make sure any setup scripts have been run and the current module version saved to the setup_module table.
    bin/magento module:status # confirm our module has been enabled!

If you want to skip over the Composer installation of the module, you can just create the app/code directory if it doesn't yet exist, and then copy in your code to the following structure: app/code/Ashsmith/Blog/.

Conclusion

We've now set up our module, along with composer! If you push to a public repo, register it with packagist you will be able to install it really easily!

Next up, I'll cover how to create your models & resource models in Magento 2.

You can view the complete module over on GitHub. Magento 2 Blog Module