dm_issue.rb

# encoding: utf-8

require "pry"
require "dm-core"
require "dm-migrations"

DataMapper::Logger.new(STDOUT, :debug)
DataMapper.setup(:default, "mysql://localhost/test")

DataMapper::Model.raise_on_save_failure = true

class Tag
  include DataMapper::Resource

  property :name, String#, required: true, length: 1..20
  property :slug, String, key: true#, auto_validation: false, unique: true, writer: :private

  # Set automatically on create, don't change.
  before(:create) do |tag|
    tag.attribute_set(:slug, self.class.generate_slug(tag.name))
  end

  def self.generate_slug(name)
    name.downcase.gsub(/\s+/, "-")
  end
end

class Tagging
  include DataMapper::Resource

  belongs_to :tag,  key: true
  belongs_to :idea, key: true
end

class Idea
  include DataMapper::Resource

  property :id, Serial
  property :name, String#, length: 4..35

  # These are skills.
  #
  # ManyToMany#Relationship#through:
  #   {:name=>:tags_provided}
  #   {:through_model=>IdeaTag} # WTF? I expect Tagging
  has n, :tags_provided, Tag, through: :taggings, via: :idea
  has n, :tags_required, Tag, through: :taggings, via: :idea
end

DataMapper.auto_migrate!