when to use @ and when to use self.

rubyonrails-talk
1

hey there, i am seeking some general info about how to get at a certain value and how to get that value in a method.

for example, lets say i have a machine. each machine has_many :sensors so sensor belongs_to :machine sensor also has_many :reports each report has a duration field that is then number of seconds since the last report of a certain value now if i wanted to add the seconds together for a total when in a certain status, i would do something like this. total = 0 for row in results   duration = row[0]   value = row[1]   if value == 'on':     total += duration

of course in rails we have sensor.value, sensor.duration so, anyway. i want to list in a table these figures.

so i need a method in sensor.rb to do this, right

so if i have for machine in machines do     <%= machine.sensor.total %>

how do i declare that ? in the Sensor class, do i have def total    i dont know what to put here to get the right sensor

and is it def total, or is it def self.total ?

thanks     so for sensor in machine.sensors |sensor| do

2

You want to do

def total … end

because you want (I assume) to get the total for that particular instance of Sensor. You would then want to do something like

def total reports.sum ‘duration’ end

Fred

– Posted via http://www.ruby-forum.com/.

method before, i assume it adds all the integers in that db field for the reports table ? thats cool too, i cant use it for this, because i can only add the ones where the status == ‘running’ but still , good thing for my notes.

again, thanks

3

wow, i am so digging this. that line replaced 9 lines of php

this is really exciting, thanks

sk