April 2010

There’s one nice side effect in the way Ohm and Sequel find records: they use [](id), which is also a way to call procs in Ruby.

So, how would you declare a reference to a DataMapper model or a set of ActiveRecord instances within Ohm?

class User < ActiveRecord::Base
  def posts
    Post.find(user: self)
  end
end

class Comment
  include DataMapper::Resource

  property :id,          Serial
  property :body,        String
end

class Post < Ohm::Model
  attribute :body
  reference :user, lambda { |id| User.find(id) }
  list      :comments, lambda { |id| Comment.get(id) }
end

Each time Ohm needs to refer to User, it will call the lambda the way it calls other Ohm models.

>> user = User.create :name => "foo"
>> post = Post.create :user => user, :body => "bar"

>> post.user.name
=> "foo"

>> comment = Comment.new
>> comment.attributes = { :body => "baz" }
>> comment.save
=> true

>> post.comments << comment
>> post.comments.first.body
>> "baz"

And what about Sequel? Because Sequel behaves exactly like Ohm, there’s no need for a lambda. You can mix them directly.

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