Very weird arel constructs

arel.rb

  # FIXME: Impossible to store the joined table in memory
  def self.all_diseases_for_cat(cat)
    cat_diseases = self.arel_table
    diseases     = Disease.arel_table

    # .joins("RIGHT OUTER JOIN #{ Disease.table_name }
    #         ON #{ self.table_name }.#{ cat_diseases[:disease_id].name }
    #          = #{ Disease.table_name }.#{ diseases[:id].name }")

    # RightOuterJoin created by me because I was bored
    scoped
    .joins(
      cat_diseases.join(diseases, Arel::Nodes::RightOuterJoin)
                    .on(cat_diseases[:disease_id].eq(diseases[:id]))
      .join_sources
    )
    .where(
      cat_diseases[:cat_id].eq(cat.id)
      .or(
        cat_diseases[:cat_id].eq(nil)
      )
    )
  end
  
module Arel
  module Nodes
    module NamedFunctions
      class Concat < Arel::Nodes::NamedFunction

        def initialize(field_ary, aliaz=nil)
          super('CONCAT', field_ary, aliaz)
        end

      end
    end
  end
end

  def self.concat_func
    cat_colors = self.arel_table

    @@func_concat ||= Arel::Nodes::NamedFunctions::Concat.new(
      [ cat_colors[:code],
        " , ",
        cat_colors[:name] ]
    )
    @@func_concat
  end
  
  def self.where_full_name(query)
    cat_colors = self.arel_table
    
    scoped
    .order(:code, :name)
    .where(
      concat_func.eq(query)
    )
  end