classification_query.rb

class ClassificationQuery
  Tag = ActsAsTaggableOn::Tag
  Tagging = ActsAsTaggableOn::Tagging

  def initialize(bill, tagger = nil)
    @bill, @tagger = bill, tagger
  end

  def count
    relation = Tag.select(Tag[:name], Arel.star.count).where(
      Tagging[:taggable_id].eq(Arel.sql("$1")).and(
        Tagging[:taggable_type].eq(Arel.sql("$2")).and(
          Tagging[:context].eq('classifications')
        )
      )
    ).joins(
      Tag.arel_table.join(Tagging.arel_table).on(
        Tag[:id].eq(Tagging[:tag_id])
      ).join_sources
    ).group(:name)

    relation.select! Arel::Nodes::NamedFunction.new(
      :bool_or, [Tagging[:tagger_id].eq(Arel.sql("$3"))]
    ) if @tagger

    # bind $* statement parameters
    relation.bind! [Tagging.columns_hash['taggable_id'], @bill.id]
    relation.bind! [Tagging.columns_hash['taggable_type'], Bill.name]
    relation.bind! [Tagging.columns_hash['tagger_id'], @tagger.id] if @tagger

    result = Tagging.connection.select_all(relation).rows.group_by(&:shift)
    result.each do |key, value|
      # type casting
      value = value.flatten
      value[0] = value.first.to_i
      value[1] = value.last == 't' if value[1]
      result[key] = value
    end

    self.class.to_h.dup.merge!(result)
  end

  def self.to_h
    @hash ||= CLASSIFICATION_NAMES.map {|n| [n, [0, false]] }.to_h.freeze
  end
end

#
# Arel Helpers
##

module ArelHelpers
  extend ActiveSupport::Concern

  module ClassMethods
    def [](name)
      arel_table[name]
    end

    alias_method :_, :[]
  end
end

ActiveRecord::Base.send(:include, ArelHelpers)