data_mapper.md

DataMapper

Start out by getting the DataMapper gem if you don't already have it, and then making sure it's in your application. A call to setup as usual will get the show started, and this example will include a 'Post' model.

require 'rubygems'
require 'sinatra'
require 'data_mapper' # metagem, requires common plugins too.

# need install dm-sqlite-adapter
DataMapper::setup(:default, "sqlite3://#{Dir.pwd}/blog.db")

class Post
  include DataMapper::Resource
  property :id, Serial
  property :title, String
  property :body, Text
  property :created_at, DateTime
end

# Perform basic sanity checks and initialize all relationships
# Call this when you've defined all your models
DataMapper.finalize

# automatically create the post table
Post.auto_upgrade!

Once that is all well and good, you can actually start developing your application!

get '/' do
  # get the latest 20 posts
  @posts = Post.all(:order => [ :id.desc ], :limit => 20)
  erb :index
end

Finally, the view at ./views/index.erb:

<% @posts.each do |post| %>
  <h3><%= post.title %></h3>
  <p><%= post.body %></p>
<% end %>

For more information on DataMapper, check out the project documentation.