Mongoid Syntax Question

In episode 189 of Railscasts, there is a named scope in the User model which is as follows:

field :roles_mask,      :type => Integer
ROLES = %w[admin moderator author]

named_scope :with_role, lambda { |role| {:conditions => "roles_mask & #{2**ROLES.index(role.to_s)} > 0"} }

 # roles related
 def roles=(roles)
  self.roles_mask = (roles & ROLES).map { |r| 2**ROLES.index(r) }.sum
 end

 def role开发者_如何转开发s
   ROLES.reject { |r| ((roles_mask || 0) & 2**ROLES.index(r)).zero? }
 end

 def role_symbols
  roles.map(&:to_sym)
 end

How would one get it to work on Mongoid as I tried the a number of options and could not get it to work?

---

That episode of Railscasts was really designed for databases that don't support arrays as native types (which Mongoid does). Then you could just create a scope which uses one of the array query criteria.

For example:

class User
  include Mongoid::Document

  field :email
  field :roles, :type => Array

  ROLES = %w[admin moderator author]

  class << self
    def with_role(*args)
      any_in(:roles => args)
    end
  end
end

This example would allow you to pass in either a single role User.with_role("admin") or an array of roles User.with_role("moderator", "author"), with the latter returning users who are either moderators or authors.

---

You can use the native map reduce mongoDB machanism which is exposed through mongoid using for_js method http://www.rubydoc.info/github/mongoid/mongoid/Mongoid/Criteria:for_js

ROLES.each_with_index do |role, role_index|
  scope "#{role.to_s.pluralize}", -> { self.for_js("(this.roles_mask & (1 << role_val)) > 0", role_val: role_index) }
end

This will give scopes in the form of:

User.admins
User.moderators
User.authors