AWITI0301 / phase-3-active-record-intro-to-rake

Intro to Rake

Learning Goals

• Introduce Rake and Rake tasks
• Understand what Rake is used for in our Ruby programs
• Learn how to build a basic Rake task

Introduction

Rake is a tool that is available to us in Ruby that allows us to automate certain jobs — anything from executing SQL to puts-ing out a friendly message to the terminal.

Rake allows us to define something called Rake tasks that execute these jobs. Once we define a task, that task can be executed from the command line.

Rake tasks have a similar utility to npm scripts in JavaScript, which you'd see in the package.json file, like npm start or npm test. They give you an easy way to run common tasks from the command line.

Why Rake?

Every program has some tasks that must be executed now and then. For example, the task of creating a database table, or the task of making or maintaining certain files. Before Rake was invented, we would either have to write standalone bash scripts to accomplish these tasks, or each developer would have to make their own decisions about what segment of their Ruby program would be responsible for executing these tasks.

Writing scripts in bash is tough, plus bash just isn't as powerful as Ruby. And for each developer to make their own somewhat arbitrary decisions about where to define and execute certain common tasks related to databases or file maintenance would be confusing. Luckily, Rake provides us a standard, conventional way to define and execute such tasks using Ruby.

Where did Rake Come From?

The C community was the first to implement the pattern of writing all their recurring system maintenance tasks in a separate file. They called this file the MakeFile because it was generally used to gather all of the source files and make it into one compiled executable file.

Rake was later developed by Jim Weirich as the task management tool for Ruby.

How to Define and Use Rake Tasks

Building a Rake task is easy. All we need to do is create a file in the top level of our directory called Rakefile. Here we define our task:

task :hello do
  # the code we want to be executed by this task
end

We define tasks with task + name of task as a symbol + a block that contains the code we want to execute.

If you open up the Rakefile in this directory, you'll see our :hello task:

task :hello do
  puts "hello from Rake!"
end

Now, in your terminal in the directory of this project, type:

$ rake hello
hello from Rake!

You should see the text above outputted to your terminal.

Describing our Tasks With rake -T

Rake comes with a handy command, rake -T, that we can run in the terminal to view a list of available Rake tasks and their descriptions. In order for rake -T to work though, we need to give our Rake tasks descriptions. Let's give our hello task a description now:

desc 'outputs hello to the terminal'
task :hello do
  puts "hello from Rake!"
end

Now, if we run rake -T in the terminal, we should see the following:

$ rake -T
rake hello       # outputs hello to the terminal

So handy!

Namespacing Rake Tasks

It is possible to namespace your Rake tasks. What does "namespace" mean? A namespace is really just a way to group or contain something, in this case our Rake tasks. So, we might namespace a series of greeting Rake tasks, like hello above, under the greeting heading.

Let's take a look at namespacing now. Let's say we create another greeting-type Rake task, hola:

desc 'outputs hola to the terminal'
task :hola do
  puts "hola desde Rake!"
end

Now, let's namespace both hello and hola under the greeting heading:

namespace :greeting do
desc 'outputs hello to the terminal'
  task :hello do
    puts "hello from Rake!"
  end

  desc 'outputs hola to the terminal'
  task :hola do
    puts "hola desde Rake!"
  end
end

Now, to use either of our Rake tasks, we use the following syntax:

$ rake greeting:hello
hello from Rake!

$ rake greeting:hola
hola desde Rake!

bundle exec rake

One common issue with Rake is the following: you run a Rake task, like rake greeting:hello, and see an output like this:

$ rake greeting:hello
rake aborted!
Gem::LoadError: You have already activated rake 10.4.2,
but your Gemfile requires rake 10.4.0.
Prepending `bundle exec` to your command may solve this.

This is a very common thing to see as a Ruby developer, and luckily, there's an easy fix if you do happen to see this error message. Just follow the instructions, and "prepend" bundle exec to your rake command:

$ bundle exec rake greeting:hello
hello from Rake!

While it is a bit of extra typing, we can tell you from experience, it's worth the effort once you start encountering this issue. If you're curious as to why, check out this article:

• But I Don't Want to bundle exec

We suggest you get in the habit of using bundle exec with your Rake commands.

Common Rake Tasks

As we move towards developing Sinatra and Rails web applications, you'll begin to use some common Rake tasks that handle certain database-related jobs. We'll be using a gem to set up some of these tasks for us, but it's still helpful to get an understanding of the syntax of Rake tasks so you can create your own.

rake db:migrate

One common pattern you'll soon become familiar with is the pattern of writing code that creates database tables and then "migrating" that code using a rake task.

Our Student class currently has a #create_table method, so let's use that method to build out our own migrate Rake task.

Note: This lesson doesn't use Active Record, so the functionality of interacting with the database is all handled within the Student class, like when we were creating our own ORMs.

We'll namespace this task under the db heading. This namespace will contain a few common database-related tasks.

We'll call this task migrate, because it is a convention to say we are "migrating" our database by applying SQL statements that alter that database.

namespace :db do
  desc 'migrate changes to your database'
  task migrate: :environment do
    Student.create_table
  end
end

But, if we run rake db:migrate now, we're going to hit an error:

rake aborted!
Don't know how to build task 'environment' (See the list of available tasks with `rake --tasks`)

Task Dependency

You might be wondering what is happening with this snippet:

task migrate: :environment do

This creates a task dependency. This line of code tells Rake that it needs to run the environment task before it can run migrate. The issue is that our Student.create_table code needs access to the config/environment.rb file because that's where the student class and database are loaded. Before we can migrate, we need to give our task access to this file, and the environment task is what will do this for us. But we haven't created the environment task yet, so let's do that.

Add the following code to the Rakefile:

task :environment do
  require_relative './config/environment'
end

Now, running bundle exec rake db:migrate should create our students table.

rake db:seed

Another task you will become familiar with is the seed task. This task is responsible for "seeding" our database with some placeholder data.

The conventional way to seed your database is to have a file in the db directory, db/seeds.rb, that contains some code to create instances of your class.

If you open up db/seeds.rb you'll see the following code to create a few students:

Student.create(name: "Melissa", grade: "10th")
Student.create(name: "April", grade: "10th")
Student.create(name: "Luke", grade: "9th")
Student.create(name: "Devon", grade: "11th")
Student.create(name: "Sarah", grade: "10th")

Then, we define a rake task that executes the code in this file. This task will also be namespaced under db:

namespace :db do

  # ...

  desc 'seed the database with some dummy data'
  task seed: :environment do
    require_relative './db/seeds'
  end
end

Now, if we run bundle exec rake db:seed in our terminal (provided we have already run rake db:migrate to create the database table), we will insert five records into the database.

If only there was some way to interact with our class and database without having to run our entire program...

Well, we can build a Rake task that will load up a Pry console for us.

rake console

We'll define a task that starts up the Pry console. We'll make this task dependent on our environment task so that the Student class and the database connection load first. Note that this class is not namespaced under :db, since we'll use it as a more general-purpose tool.

desc 'drop into the Pry console'
task console: :environment do
  Pry.start
end

Now, provided we ran rake db:migrate and rake db:seed, we can drop into our console with the following:

$ bundle exec rake console

This should bring you into a Pry session in your terminal:

[1] pry(main)>

Let's check to see that we did in fact successfully migrate and seed our database:

Student.all
# => [[1, "Melissa", "10th"],
#  [2, "April", "10th"],
#  [3, "Luke", "9th"],
#  [4, "Devon", "11th"],
#  [5, "Sarah", "10th"]]

We did it!

Conclusion

As developers, we are constantly iterating and experimenting on our code. To make our lives easier, it's helpful to use a tool like Rake to automate some of the common setup and testing tasks we need to run in order to interact with our applications. Using Rake is a great way to speed up your development process — any time you find yourself running the same code over and over again, consider setting up a Rake task for it.

Resources

• The Rake Gem
• Writing Custom Rake Tasks