POST method in ruby does not insert data into the table - ruby

Question

I just started to learn programming. I study the book Jump start Sinatra by Darren Johnson.
I did everything as stated in the book, but insert a new entry in the table at me is not working. I click on the button "Save Song" but nothing happens.
At the same time modify existing records I can.
My main.rb
require 'sinatra'
require 'sinatra/reloader' if development?
require 'slim'
require 'sass'
require './song'
set :public_folder, 'public'
set :views, 'views'
get('/styles.css'){ scss :styles }
get '/' do
slim :home
end
get '/about' do
#title = "All About This Website"
slim :about
end
get '/contact' do
slim :contact
end
not_found do
slim :not_found
end
My song.rb
require 'dm-core'
require 'dm-migrations'
configure do
DataMapper.setup(:default, "sqlite3://#{Dir.pwd}/development.db")
end
class Song
include DataMapper::Resource
property :id, Serial
property :title, String
property :lyrics, Text
property :length, Integer
property :released_on, Date
def released_on=date
super Date.strptime(date, '%m/%d/%Y')
end
end
DataMapper.finalize
get '/songs' do
#songs = Song.all
slim :songs
end
get '/songs/new' do
#song = Song.new
slim :new_song
end
get '/songs/:id' do
#song = Song.get(params[:id])
slim :show_song
end
post '/songs' do
song = Song.create(params[:song])
redirect to("/songs/#{song.id}")
end
get '/songs/:id/edit' do
#song = Song.get(params[:id])
slim :edit_song
end
put '/songs/:id' do
song = Song.get(params[:id])
song.update(params[:song])
redirect to("/songs/#{song.id}")
end
My views/song_form.slim
label for="title" Title:
input#title type="text" name="song[title]" value="#{#song.title}"
label for="length" Length:
input#length type="number" name="song[length]" value="#{#song.length}"
label for="released_on" Date(mm/dd/yyyy):
input#released_on type="text" name="song[released_on]" value="#{#song.released_on.strftime("%m/%d/%Y") if #song.released_on}"
label for="lyrics" Lyrics:
textarea#lyrics name="song[lyrics]" == #song.lyrics
input type="submit" value="Save Song"
My views/edit_song.slim
h1 Edit Song
form method="POST" action="/songs/#{#song.id}"
input type="hidden" name="_method" value="PUT"
== slim :song_form
When I try to add a new table record in IRB:
irb(main):001:0> require './song'
NoMethodError: undefined method `get' for main:Object
from /media/kamrenov/other/work/sinatra/song.rb:21:in `<top (required)>'
from /home/kamrenov/.rbenv/versions/2.2.1/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /home/kamrenov/.rbenv/versions/2.2.1/lib/ruby/2.2.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from (irb):1
from /home/kamrenov/.rbenv/versions/2.2.1/bin/irb:11:in `<main>'