Update rails database entire column with complex calculation function

Question

I have a rails table. (normalusers)=> id, parent_id, Height. I have added the height column afterward. Now I want to add value to it. Is there any way I can achieve this? I have tried migration but it is not updating heights. I think functions do not work in migration. After migration, all the rows have the value of height same as before.

class Latest < ActiveRecord::Migration[6.0]

  def change
      i = 1
    loop do
          i += 1
          puts i
          record=Normaluser.find(i)
          record.height=get_height(record)
          record.save!
          if i == 39
            break       # this will cause execution to exit the loop
          end
    end
  end
  def get_height(record)
      maxHeight=0
      Normaluser.where(pid: record.id).each do |f|
          tempHeight=get_height(f)
          if tempHeight > maxHeight
              maxHeight=tempHeight
          end     
      end
      return maxHeight
  end
end

Please mention what is not working? Is there any error that you are facing? — Gautam
– Gautam, Commented Feb 10, 2020 at 14:45
Yes, there is nothing wrong in writing functions. I think you should debug to see that the value received from get_height function is correct. — Gautam
– Gautam, Commented Feb 10, 2020 at 15:05
@Gautam Where to see the output of put statement? It is not visible in the terminal. — code0079
– code0079, Commented Feb 10, 2020 at 16:48
You should be able to see the output of the puts statement when you run the migration. — Gautam
– Gautam, Commented Feb 10, 2020 at 16:56

Rajdeep Singh · Accepted Answer · 2020-02-10 15:09:21Z

1

The best way to run a one time script to update existing columns of a table is to write a rake task.

in lib/tasks/ directory, create a file named update_height.rake, in that file

namespace :update_latest_records do
  desc 'Update height column of existing Latest'
  task height: :environment do
    # your update logic goes here
  end
end

Then in project home, run the rake command

RAILS_ENV=development rake update_latest_records:height

Pass correct RAILS_ENV value in each environment, e.g. to update the records in production server it should be RAILS_ENV=production

Hope that helps!

answered Feb 10, 2020 at 15:09

Rajdeep Singh

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