Can't populate data to newly added column using rails migration

Question

I've just created a migration in rails to add a column to an existing table. Below is sample codes

class AddShortInfoToDepartment < ActiveRecord::Migration
  def self.up
    add_column :departments, :short_info, :string
  end

  def self.down
    remove_column :departments, :short_info, :string
  end
end

Beforehand, I've created a task file to seed the column.

namespace :db do
  namespace :seed do
    desc "seed short_info into table departments"
    task department_short_info: :environment do
      short_infos = [
        "Management and Administration",
        "Financial",
        "Clinical",
        "Clinical Support",
        "Patient Diet and Ration Management",
        "Health Record Management"
      ]

      Department.all.each_with_index do |department, index|
        department.update(short_info: short_infos[index])
      end

    end
  end
end

then I call the task in the migration file by adding a line:

class AddShortInfoToDepartment < ActiveRecord::Migration
  def self.up
    add_column :departments, :short_info, :string

    # seeding column short_info using rake task
    Rake::Task['db:seed:department_short_info'].invoke
  end

  def self.down
    remove_column :departments, :short_info, :string
  end
end

and finally, I ran the migration

rake db:migrate

There was no error in both during adding new column and during running rake task.

But, when I checked using console after migration done, the column "short_info" in the table has no data and returns nil.

To make sure that the rake task does it's work as intended, I ran the task using rake db:seed:department_short_info and it was successful and the column was seeded.

Is there a step that I missed or any command that I should run first before I run the migration?

Did you migrate before adding the task invocation, and then trying to migrate again? if so, you need to rollback the migration first, then do it again. — Moamen Naanou
– Moamen Naanou, Commented Mar 5, 2018 at 5:25
And you can replace update with update! to check if there's any validation error happens. — Moamen Naanou
– Moamen Naanou, Commented Mar 5, 2018 at 5:31
Yes @MoamenNaanou i did. This is just a sample coding to post here. The actual coding is more completed just like you suggest. — yusdirman
– yusdirman, Commented Mar 5, 2018 at 6:25

nekogami · Accepted Answer · 2018-03-05 06:14:41Z

2

If I remember correctly, when you want to do a migration AND execute a seed task inside it, you have to execute #reset_column_information on the models you are going to use, in your case

Department.reset_column_information

That being said, beware of these kind of things since it can slow down a lot of your push in production depending on your dataset size.

answered Mar 5, 2018 at 6:14

nekogami

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