gistfile1.rb

# our multi_group http://rails.lighthouseapp.com/projects/8994/tickets/120-patch-activerecord-calculations-only-accept-one-grouping-field#
# isn't updated for 2.2 yet. In the meantime, this poor man's version gives you the same results with some delimitter tom foolery.
# 
# note: be careful to ensure that your group_by do not use the delimitter 
# usage:
#   self.multi_count(:id, :distinct => true, :group => [:symptom_id, :treatment_id])        
#   [[["138", "1018"], 187], [["138", "427"], 373], [["6", "1018"], 197], [["6", "427"], 393]]
class ActiveRecord::Base  
  def self.multi_count(field, opts = {})
    fq_field_name = "#{table_name}.#{field}"
    count_statement = opts[:distinct] ? "count (distinct #{fq_field_name})" : "count(#{fq_field_name})" 
    sql_opts = {}
    select_cols = []
    if opts[:group]
      Array(opts[:group]).each do |group_term|
        select_cols << group_term
      end
      group_str = (2..opts[:group].length+1).to_a.join(',')
    end
    if opts[:order]
      order_opts = Array(opts[:order])
      order_opts.each do |order_term|
        select_cols << order_term
      end
      sql_opts[:order] = if opts[:group]
        select_cols.length/2+2..select_cols.length+1
      else
        2..select_cols.length+1
      end.to_a.join(',') + ' NULLS LAST'

    end

    sql_opts[:group] = (2..select_cols.length+1).to_a.join(',')
    select_statement = "#{count_statement}, #{select_cols.join(',')}"

    #build a sql query
    sql = construct_finder_sql(sql_opts.merge(:select => select_statement))
    connection.select_rows(sql).inject(ActiveSupport::OrderedHash.new) do |memo, row|
      key = row.slice(1,opts[:group].length)
      memo[key.length > 1 ? key : key.first] = row[0].to_i
      memo
    end
  end
end