## models/Interpolate.rb

#Class to store interpolated data derived fro readings
class Interpolation < ActiveRecord::Base

  # holds readings that should be interpolated
  attr_reader :readings
  attr_reader :rdates
  attr_reader :rdiff_counter_days
  attr_reader :rdiff_co2_days

  rec = nil

  # Class to calculate interpolation for each day
  def self.calc(unit_id, type)
   #get all readings
   @readings = Reading.find_all_by_unit_id_and_type(unit_id,type, :select => "date, diff_counter_days, diff_co2_days", :order => "date asc")
   #init arrays
   @rdates = []
   @rdiff_counter_days = []
   @rdiff_co2_days = []
   #send readings to arrays
   @readings.each do |r|
     @rdates << r.date
     @rdiff_counter_days << r.diff_counter_days
     @rdiff_co2_days << r.diff_co2_days
   end

   #iterate down through each day in the period
   day = @rdates.last
   diff_counter_days = @rdiff_counter_days.last
   diff_co2_days = @rdiff_co2_days

   while day>=@rdates.first do
     #check if day has reading
     if i=@rdates.rindex(day)
       print "match! : "
       # set interpolated fields with matched data
       diff_counter_days = @rdiff_counter_days[i]
       diff_co2_days = @rdiff_co2_days[i]
     end
     # debug output
     print day
     print ": "
     print diff_counter_days
     print ", "
     print diff_co2_days
     print "\n"

     # check update if exist or create new  if not
     rec = Interpolation.find(:first, :conditions =>  ["unit_id = ? and date = ? and type = ?", unit_id, day, type] )
     if rec
       rec.update_attributes(:diff_counter_days => diff_counter_days, :diff_co2_days => diff_co2_days )
       puts "update"
     else
       puts "create"
       rec = Interpolation.new(:type => type, :date => day, :diff_counter_days => diff_counter_days, :diff_co2_days => diff_co2_days )
       rec.save
     end

     # decrease day by one
     day=day.yesterday
   end
  end
end

## somehow updates use the wrong class.  They update Reading and not Interpolate

Loading development environment (Rails 2.3.2)
>> rec = Interpolation.find(:first, :conditions =>  ["unit_id = ? and date = ? and type = ?", 1, "2009-05-07", "ElectricityReading"] )
=> #<ElectricityReading id: 1, unit_id: 1, type: "ElectricityReading", date: "2009-05-07", created_at: nil, updated_at: nil, diff_counter_days: #<BigDecimal:18a6adc,'0.123E3',4(8)>, diff_co2_days: #<BigDecimal:18a69d8,'0.234E3',4(8)>>
>> rec.diff_counter_days =0
=> 0
>> rec.save!
=> true
>> rec = Interpolation.find(:first, :conditions =>  ["unit_id = ? and date = ? and type = ?", 1, "2009-05-07", "ElectricityReading"] )
=> #<ElectricityReading id: 1, unit_id: 1, type: "ElectricityReading", date: "2009-05-07", created_at: nil, updated_at: nil, diff_counter_days: #<BigDecimal:183ebbc,'0.123E3',4(8)>, diff_co2_days: #<BigDecimal:183e9f0,'0.234E3',4(8)>>