Sinatra Activerecord Setup

Objectives

Setup a database in a Sinatra application.
Create and use a Rakefile to run ActiveRecord migrations.
Use ActiveRecord in a Sinatra application.

Overview

Sinatra doesn't come with database support out of the box, but it's relatively easy to configure. In general, we'll be working from templates that have this pre-built, but it's good to understand what's going on under the hood. We're going to practice adding a database to our Sinatra applications.

Instructions

Fork and clone this repository to get started! We have a basic sinatra application stubbed out with an app.rb file acting as the controller.

Adding Your Gems

First, we'll add three gems to allow us to use ActiveRecord: activerecord version 4.2.5, sinatra-activerecord, and rake. activerecord gives us access to the magical database mapping and association powers. rake, short for "ruby make", is a package that lets us quickly create files and folders, and automate tasks such as database creation, and sinatra-activerecord gives us access to some awesome Rake tasks. Make sure those three gems are in your Gemfile:

  gem 'sinatra'
  gem 'activerecord', '4.2.5'
  gem 'sinatra-activerecord'
  gem 'rake'
  gem 'thin'
  gem 'require_all'

Into our development group, we'll add two other gems: sqlite3 and tux. sqlite3 is our database adapter gem - it's what allows our Ruby application to communicate with a SQL database. tux will give us an interactive console that pre-loads our database and ActiveRecord relationships for us. Since we won't use either of these in production, we put them in our :development group - this way, they won't get installed on our server when we deploy our application.

  gem 'sinatra'
  gem 'activerecord', '4.2.5'
  gem 'sinatra-activerecord'
  gem 'thin'
  gem 'require_all'

  group :development do
    gem 'shotgun'
    gem 'pry'
    gem 'tux'
    gem 'sqlite3'
  end

Our Gemfile is up to date - awesome! Go ahead and run bundle install to get your system up to speed.

Connecting to the Database

We now have access to all of the gems that we need, but we still need to set up a connection to our database. Add the following block of code to your environment.rb file (underneath Bundler.require(:default, ENV['SINATRA_ENV'])).

configure :development do
  set :database, 'sqlite3:db/database.db'
end

This sets up a connection to a sqlite3 database named "database.db", located in a folder called "db." If we wanted our .db file to be called dogs.db, we could simply change the name of this file:

configure :development do
  set :database, 'sqlite3:db/dogs.db'
end

But for now, database.db is a great name. Notice that this didn't actually create those files or folders yet - that's how Rake will help us.

Making a Rakefile

As we mentioned, rake gives us the ability to quickly make files and set up automated tasks. We define these in a file called Rakefile. First, create a Rakefile in the root of our project directory. In the Rakefile, we'll require our config/environment.rb file to load up our environment, as well as "sinatra/activerecord/rake" to get Rake tasks from the sinatra-activerecord gem.

require './config/environment'
require 'sinatra/activerecord/rake'

In the terminal, type rake -T to view all of the available rake tasks. You should see the following output:

rake db:create              # Creates the database from DATABASE_URL or config/database.yml for...
rake db:create_migration    # Create a migration (parameters: NAME, VERSION)
rake db:drop                # Drops the database from DATABASE_URL or config/database.yml for t...
rake db:fixtures:load       # Load fixtures into the current environment's database
rake db:migrate             # Migrate the database (options: VERSION=x, VERBOSE=false, SCOPE=blog)
rake db:migrate:status      # Display status of migrations
rake db:rollback            # Rolls the schema back to the previous version (specify steps w/ S...
rake db:schema:cache:clear  # Clear a db/schema_cache.dump file
rake db:schema:cache:dump   # Create a db/schema_cache.dump file
rake db:schema:dump         # Create a db/schema.rb file that is portable against any DB suppor...
rake db:schema:load         # Load a schema.rb file into the database
rake db:seed                # Load the seed data from db/seeds.rb
rake db:setup               # Create the database, load the schema, and initialize with the see...
rake db:structure:dump      # Dump the database structure to db/structure.sql
rake db:structure:load      # Recreate the databases from the structure.sql file
rake db:version             # Retrieves the current schema version number

Testing it Out

Let's test out our handiwork by creating a dogs table with two columns: name and breed. First, let's create our migration:

rake db:create_migration NAME=create_dogs

You should see the following output:

=># db/migrate/20150914201353_create_dogs.rb

The beginning of the file is a timestamp - yours should reflect the time that your create_dogs file was created! You've now created your first database migration inside of the db folder.

Inside of the migration file, remove the default change method (we'll come back to this), and add methods for up and down.

class CreateDogs < ActiveRecord::Migration
  def up
  end

  def down
  end
end

Our up method should create our table with name and breed columns. Our down method should drop the table.

class CreateDogs < ActiveRecord::Migration
  def up
    create_table :dogs do |t|
      t.string :name
      t.string :breed
    end
  end

  def down
    drop_table :dogs
  end
end

Now, run the migration from the terminal with rake db:migrate.

rake db:migrate SINATRA_ENV=development

Why add SINATRA_ENV=development, you might ask? Well, remember the top line of config/environment.rb? It's telling Sinatra that it should use the "development" environment for both shotgun and the testing suite. Therefore, we want to make sure our migrations run on the same environment as well, and specifying SINATRA_ENV=development allows us to do that.

You should see the following output:

== 20150914201353 CreateDogs: migrating =======================================
-- create_table(:dogs)
   -> 0.0019s
== 20150914201353 CreateDogs: migrated (0.0020s) ==============================

The `change` Method

The change method is actually a shorter way of writing up and down methods. We can refactor our migration to look like this:

class CreateDogs < ActiveRecord::Migration
  def change
    create_table :dogs do |t|
      t.string :name
      t.string :breed
    end
  end

end

While the rollback (down) method is not included, it's implicit in the change method. Rolling back the database would work in exactly the same way as using the down method.

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