sudo gem install sequel sinatra-sequel
sudo gem install sqlite3
sudo gem install mysql
sudo gem install postgres

require 'sinatra'
require 'sinatra/sequel'

# Establish the database connection; or, omit this and use the DATABASE_URL
# environment variable as the connection string:
set :database, 'sqlite://foo.db'

# At this point, you can access the Sequel Database object using the
# "database" object:
puts "the foos table doesn't exist" if !database.table_exists?('foos')

# define database migrations. pending migrations are run at startup and
# are guaranteed to run exactly once per database.
migration "create teh foos table" do
  database.create_table :foos do
    primary_key :id
    text        :bar
    integer     :baz, :default => 42
    timestamp   :bizzle, :null => false

    index :baz, :unique => true
  end
end

# you can also alter tables
migration "everything's better with bling" do
  database.alter_table :foos do
    drop_column :baz
    add_column :bling, :float
  end
end

# models just work ...
class Foo < Sequel::Model
  many_to_one :bar
end

# see:
Foo.filter(:baz => 42).each { |foo| puts(foo.bar.name) }

# access the database within the context of an HTTP request
get '/foos/:id' do
  @foo = database[:foos].filter(:id => params[:id]).first
  erb :foos
end

# or, using the model
delete '/foos/:id' do
  @foo = Foo[params[:id]]
  @foo.delete
end