Managing Dependencies

In every web application, there are common tasks that you need to do (e.g authenticate users or query a database). Libraries are useful for not reinventing the wheel, and in Ruby they are often referred to as gems.

Ruby uses Rubygems to distribute them and to ease the installation. Installing Cuba is as easy as typing gem install cuba in the command line.

Even though Rubygems is useful when installing gems, it has its limitations. Unfortunately, it installs all gems globally. It means that if you have different versions of a gem installed, you have to make sure that you require the right version for your project.

Bundler is one of the most used tools to solve this problem. It has approximately ~10k lines of code, that's more than all the dependencies of this project put together. Because of this complexity, we'll use a different approach in this book.

"The Right Way"

Back to the original problem, we need a way to keep track of the dependencies and install the right version of each one. This is where gs and dep come to the rescue.

With gs you can create a gemset for each project. A gemset is an isolated space to install gems. By providing each project with their own gemset, you can be sure that the right version of a gem is loaded.

While gs handles the gemset, dep keeps track of the dependencies for your project, making sure that all the dependencies are met.

To install gs and dep, use the gem install command:

$ gem install gs
$ gem install dep

Before installing the dependencies of this project, you need a gemset. Creating one is as easy as typing:

$ gs init

This command does two things. First, it creates a directory .gs, where Rubygems will install the dependencies. Secondly, it starts a shell session and set the .gs folder as the path where Ruby will look for gems.

Now that we created a local gemset, it's time to install the dependencies for our project. dep uses a .gems file to keep track of the required dependencies for the application. This file lists the gems with their version numbers.

In our application's folder, you will find the .gems file that contains the dependencies we'll use in this book. We'll talk more about each gem later.

cuba -v 3.1.1
cuba-contrib -v 3.1.0
cutest -v 1.2.1
ohm -v 2.0.0
mote -v 1.1.2
scrivener -v 0.2.0
rack-protection -v 1.5.3
rack-test -v 0.6.2
shield -v 2.1.0
shotgun -v 0.9

Finally, we need to install the gems by running:

$ dep install

This simply does a gem install for each dependency on the list. dep also has features for adding and removing dependencies. To read more about dep, visit their home page.

NOTE: It's important to mention that together, gs and dep, only have 200 lines of code and don't add any memory footprint to your application.

NOTE: bs and gst are interesting implementations of gs in bash.