我后来安装了PostgreSQL

1 - 已安装的ruby pg

2 - 已安装的ruby：

gem install activerecord
gem install sinatra-activerecord
gem install rake
3 - 我创建了连接数据库到app.rb的文件

app.rb

configure :development do set :database, {adapter: "postgresql", encoding: "unicode", database: "your_database_name", pool: 2, username: "your_username", password: "your_password"}
end

configure :production do
set :database, {adapter: "postgresql", encoding: "unicode", database: "your_database_name", pool: 2, username: "your_username", password: "your_password"}
end
4 - 创建app.rb文件的模型

class Article < ActiveRecord::Base
end
5 - 创建到Rakefile的迁移

require 'sinatra/activerecord'
require 'sinatra/activerecord/rake'
require './app'
6 - rake db:create_migration NAME=create_articles

7 - 在由文件迁移创建的新文件中

class CreateArticles < ActiveRecord::Migration

def change
    create_table :articles do |t|
      t.string :title
      t.string :content
      t.boolean :published, :default => false
      t.datetime :published_on, :required => false
      t.integer :likes, :default => 0
      t.timestamps null: false
    end
  end
end 

8 - 我完成了命令db:create和rake db:migration

创建数据库，显示psql控制台中的数据库。现在如何在sinatra中添加数据库线？