June 29, 2016

Creating models in Rails

This is my memo on Creating models in Rails.

Create models and migration files (database schema)

rails generate model NAME [field[:type][:index] field[:type]

Migrate the database

$ rake db:migrate
== 20160624190709 CreateArtists: migrating ====================================
-- create_table(:artists)
   -> 0.0247s
== 20160624190709 CreateArtists: migrated (0.0248s) ===========================
...

In case, you need to reset the database, run

$ rake db:migrate:reset

Create a seed file and fill the database with sample database

This allows us to check if database is working as we expects before moving on to actually writing application code.
Use create! instead of create so that we can detect syntax error easily.

require_relative './song_data.rb'
require_relative './artist_data.rb'

# Clear all the data in the database.
Song.destroy_all   # Dependent
Artist.destroy_all

# Get data from files.
song_data   = get_song_data()
artist_data = get_artist_data()

# Associate artist to his/her songs.
song_data.each_pair do |artist_name, songs|
  info = artist_data[artist_name]
  current_artist = Artist.create!({
    name:         info[:name],
    photo_url:    info[:photo_url],
    nationality:  info[:nationality]
  })

  songs.each do |song|
    Song.create!({
      title:        song[:title],
      album:        song[:album],
      preview_url:  song[:preview_link],
      artist:       current_artist
    })
  end
end

$ rake db:seed

Check if the data is successfully injected into the database.

$ rails c
>> Song.all
  Song Load (2.3ms)  SELECT "songs".* FROM "songs"
=> #<ActiveRecord::Relation []>
>> Artist.all.length
  Artist Load (2.3ms)  SELECT "artists".* FROM "artists"
=> 5
>> Song.all.length
  Song Load (2.1ms)  SELECT "songs".* FROM "songs"
=> 250
>>