Question

I have a table with workouts with the following key columns:

workout_id      distance
1                       2.3
2                       3.1

Let’s say I want to write a Rails active record query so that I get these columns plus a running total of the distance, like so:

workout_id      distance      running_total
1                       2.3                 2.3
2                       3.1                 5.4

How could I do such a thing?

Answer 1

I agree with HungryCoder that you should perhaps do it in the model rather than in a database query.

class Workout
  # ...
  attr_accessor :running_total
  class << self
    def distance_with_running_total
      total = 0.0
      Workout.order(:id).collect do |w|
        total += w.distance
        w.running_total = total
      end
    end
  end
  # ...
end

Then in the controller, simply do:

@workouts = Workout.distance_with_running_total