Create a Blog in Ruby and Sinatra - Part 2 - Models

This is part 2 of my Sinatra blog tutorial. Today I’m talking about the database layer. Don’t forget to check out the full source of my blog on github.

Source on Github

I used sequel as the ORM for this blog. I had originally wanted to use DataMapper, but I ran into some problems. They’re pretty similar anyway.

First, we need to give the connection information to Sequel. I put my database info in a yaml file because I wanted to be able to pass the command-line migration tool the same info. I require this file from my “controller”. It’s important to remember that the following files aren’t a sinatra standard or anything. You can organize your files however you like.

data/init.rb

require 'rubygems'
require 'sequel'
require 'yaml'

content = File.new("data/database.yml").read
settings = YAML::load content
DB = Sequel.connect "#{settings['adapter']}://#{settings['username']}:#{settings['password']}@#{settings['host']}/#{settings['database']}"

require 'data/models'

data/database.yml

adapter: mysql
host: localhost
username: root
password: root
database: custom_blog

Here are my models. The syntax of these models will look similar to active record. There aren’t much to them. A few things to notice are that I used simple many_to_many and one_to_many associations.

data/models.rb

require 'rubygems'
require 'sequel'

class Post < Sequel::Model
  Page = "page"
  Post = "post"

  many_to_many :tags
  one_to_many :comments

  def date
    created.strftime "%B %d, %Y"
  end

  def summary(length=300)
    body.gsub(/(<[^>]*>)|\n|\t/s," ")[0..length]
  end

  def update_title(value)

    raise "[ ! ] Could not find title for post" if value.nil?

    self.title = value
    self.name = value.downcase.gsub(/[^\w]/,"_").gsub(/__/,"")
  end
end

class Tag < Sequel::Model
  many_to_many :posts, :order => :created.desc
end

class Comment < Sequel::Model
  many_to_one :posts

  def post
    Post[:id => post_id]
  end
end

These behave as expected. The syntax is only slightly different from active record. Sequel allows you to chain commands to a dataset together, which makes it easy to create complex queries.

Post.all
Post.first.comments
Post.filter(:kind => Post::Page).reverse_order(:created).all
Post.first.tags

I’ll give you more concrete examples when we cover the controller. The next thing to look at is the migration. Now, I don’t really like migrations, but until these ORMs add support to dynamically update the database schema, I’m stuck with them. Here’s where I’m at currently.

data/001_BaseSchema.rb

require 'data/models'

class BaseSchema < Sequel::Migration
  def up
    create_table! :posts do
      primary_key :id
      String :title
      Text :body
      Time :mtime
      Time :created
      String :kind, :default => Post::Post
      String :file
      String :name
    end

    create_table! :tags do 
      primary_key :id
      String :name
    end

    create_table! :posts_tags do
      primary_key :id
      foreign_key :tag_id, :tags
      foreign_key :post_id, :posts
    end      
  end

  def down
    drop_table :posts
    drop_table :tags
    drop_table :posts_tags
  end
end

data/002_Comments.rb

require 'data/models'

class Comments < Sequel::Migration
  def up
    create_table! :comments do
      primary_key :id
      foreign_key :post_id, :posts

      String :name
      String :email
      String :url
      Text :body
    end
  end

  def down
    drop_table :comments
  end
end

To run the migrations, you use the sequel command-line tool. Here, I’m telling it to run migrations from my data folder, and to use data/database.yml for connection info.

sequel -m data data/database.yml
sequel -m data data/database.yml -M 1 # migrates to 001

That’s it for now!