Arel Scopes

arel_scopes.rb

module ArelScopes
  extend ActiveSupport::Concern

  module ClassMethods
    
    # Create chainable arel scopes
    # Example:  
    # class Post 
    # arel_scope :published, lambda { arel_table[:published_at].gteq(Time.now) }
    # arel_scope :written_by, lambda { |user| arel_table[:author_id].eq(user.id) }
    # arel_scope :approved, arel_table[:approved].eq(true)
    # scope :viewable_by, lambda { |user| where(written_by_as_arel(user).or(published_as_arel.and(approved_as_arel)))
    # ....
    #
    # Gives you: 
    # Post.published
    # Post.written_by(User.find_by_username("Bill")
    # Post.viewable_by(User.find(12))
    # Post.where( Post.published_as_arel.or(Post.approved_as_arel)
    def arel_scope(name, arel_scope_options={})
      if arel_scope_options.is_a? Proc
        scope(name, lambda { |*args| where(arel_scope_options.call(*args)) })
        scope_proc = arel_scope_options
      else
        scope(name, where(arel_scope_options) )
        scope_proc = lambda { arel_scope_options }
      end

      singleton_class.send(:redefine_method, (name.to_s+"_as_arel").to_sym, &scope_proc)

    end
  end
end