how to run migration file with ruby script

Question

The Book model have

name column
author column
ad column (I want to add)

I would like to add 'Mr' to the name column and add them to the ad column. For that, I wanted to write a script with migration file, but it did not work. What should I do? Thanks

class AddAdToBooks < ActiveRecord::Migration
  def change
    add_column :books, :ad, :string

    Book.all.each do |book|
      book.ad = 'Mr.' + name
      book.save
    end
  end
end

It could not move if I thought the script would work. And I tried changed one it also doesn't work. — johnny
– johnny, Commented Feb 23, 2017 at 7:29

Deepak Mahakale · Accepted Answer · 2017-02-23 07:28:48Z

2

I this you can achieve that using raw query. It's always better to execute raw query unless you want to run the Model callbacks.

class AddAdToBooks < ActiveRecord::Migration
  def change
    add_column :books, :ad, :string

    if ActiveRecord::Base.connection.adapter_name.downcase.include? "mysql"
      execute "UPDATE books SET ad = CONCAT('Mr. ', name)"
    else
      execute "UPDATE books SET ad = 'Mr. ' || name"
    end
  end
end

The problem with the following

Book.all.each do |book|

It will load all records even if you have 1 million records in memory and loop over it.
Also, It will run all the callbacks for that model.

answered Feb 23, 2017 at 7:28

Deepak Mahakale

23.8k10 gold badges73 silver badges94 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

how to run migration file with ruby script

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related