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New article: Dependency management in PHP project 2

Cinan Rakosnik authored on 07/12/2013 at 23:17:45
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+---
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+layout: post
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+title: "Dependency management in PHP projects #2"
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+date: 2013-12-08 00:25
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+comments: true
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+categories: [webdev, php]
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+cover: /images/cover/avatar.png
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+keywords: php, composer, bundle, versions, dependencies, packages, libraries
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+description:
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+---
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+
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+In the last [article](/2013/11/24/dependency-management-in-php-projects/) about
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+dependency management I've explained why we, PHP programmers, need [composer](http://getcomposer.org/)
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+and why you should use it in your PHP projects.
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+
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+Let's dig deeper in composer internals.
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+
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+# Where can I find packages for composer?
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+
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+Many of packages which we can use as project dependencies can be found on [packagist](https://packagist.org/).
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+
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+# Dependency versioning
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+
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+Let's say our project depends on [Twig](http://twig.sensiolabs.org/) library.
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+The ```require``` section in ```composer.json``` file will look like this:
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+
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+{% codeblock lang:json %}
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+	"require": {
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+        "twig/twig": "1.12.*"
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+    }
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+{% endcodeblock %}
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+
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+The file says we want Twig version at least 1.12.0. Composer will install the newest
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+minor version (e.g. 1.12.1 or 1.12.3) of major version 1.12. We'll never get Twig
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+1.11 or Twig 1.13 or Twig 2.0.
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+
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+We can define an exact version of Twig like this: ```"twig/twig": "1.12.1"```.
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+
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+Maybe we want any newest development version. It's simple: ```"twig/twig": "dev-master"```.
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+Now composer will install newest bleeding-edge version from ```master``` branch
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+from Twig's [Git repository](https://github.com/fabpot/Twig). The used schema
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+is: ```dev-<branch>```.
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+
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+# Using custom dependencies
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+
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+If you have your own libraries you want to use in a project, add ```repositories``` section
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+to the ```composer.json```. It contains array of
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+<abbr title="Version Control System">[VCS](http://en.wikipedia.org/wiki/Revision_control)</abbr>
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+repositories.
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+
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+Let's say you want to use a library hosted on github. Then the ```repositories```
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+section can look like this:
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+
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+{% codeblock lang:json %}
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+	"repositories": [
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+		{
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+			"type": "git",
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+			"url": "https://github.com/vendor/example.git"
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+		}
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+	]
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+{% endcodeblock %}
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+
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+In ```type``` field we said it's a Git repository and an address of the repository
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+is defined in ```url``` field.
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+
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+Then, you can edit the ```require``` section:
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+
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+{% codeblock lang:json %}
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+	"require": {
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+		"twig/twig": "1.12.*",
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+		"vendor/example": "dev-master"
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+	}
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+{% endcodeblock %}
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+
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+Now ```composer update``` will fetch code of "example" library from ```https://github.com/vendor/example.git```
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+repository.
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+
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+# How my project knows about installed dependencies?
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+
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+Composer creates ```autoload.php``` file in ```vendor``` directory. The file takes care
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+of *dynamic* autoloading of all dependencies. Dynamic means all required files are loaded
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+when they are needed. If we had defined 20 dependencies, it would be very inefficient
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+and slow to load all files.
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+
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+When some dependency class is used for the first time, composer's Autoloader gets called
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+and tries to find and load needed files.
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+
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+I believe an example below enlightens the question. All you need to do is to include
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+```autoload.php``` file in your project.
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+
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+{% codeblock index.php lang:php %}
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+	<?php
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+
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+	// load autoload.php
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+	require 'vendor/autoload.php';
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+
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+	// how many files has been loaded so far
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+	echo "Number of loaded files: " . count(get_included_files()) . "\n";
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+
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+	// can use Twig class
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+	$loader = new Twig_Loader_String();
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+
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+	echo "Number of loaded files: " . count(get_included_files()) . "\n";
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+{% endcodeblock %}
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+
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+The example is very simple, I just wanted to show dependency autoloading **just works**.
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+By the way, the output is:
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+
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+	Number of loaded files: 6
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+	Number of loaded files: 9
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+
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+First time a counter was called there were loaded only composer files. Next time
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+composer loaded more files required by Twig.
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+
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+Very interesting topic about autoloading of your own code is explained on composer
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+official [guide](http://getcomposer.org/doc/01-basic-usage.md#autoloading).
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+
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+
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+*This article was also published on my school [blog](http://cinan.blog.matfyz.sk/p106605-dependency-management-in-php-projects-#2).*
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