How do I add some inserts in rails migration?

Edit: PLEASE NOTE - Posters above are correct, you should not populate the DB inside migrations. Don't use this to add new data, only to modify data as part of changing the schema.

For many things, using raw SQL will be preferable, but if you need to insert data as part of a migration (for instance, doing data conversion when breaking out a table into multiple tables), and you want some default AR stuff like convenient DB-independent escaping, you can define a local version of the model class:

class MyMigrationSucksALittle < ActiveRecord::Migration
  class MyModel < ActiveRecord::Base
    # empty guard class, guaranteed to have basic AR behavior
  end

  ### My Migration Stuff Here
  ### ...

end

Note that this works best for simple cases; since the new class is in a different namespace (MyMigrationSucksALittle::MyModel), polymorphic associations declared in the guard model won't work correctly.

A somewhat more detailed overview of available options is located here: http://railsguides.net/2014/01/30/change-data-in-migrations-like-a-boss/

Don't. If you're looking for seed data, you should use db/seeds.rb and rake db:seed instead. More info in this Railscast.

Side note: Always make sure that the code in db/seeds.rb is idempotent. i.e. It should always be safe to re-run your seeds.

But, if you must insert or modify data inside a migration (there are legitimate use-cases for this), it's best to use SQL statements instead. Your model class isn't guaranteed to still be around in the same form in a future version of your application, and running the migrations from scratch in the future might yield errors if you reference the model class directly.

execute "insert into system_settings (name, label, value) values ('notice', 'Use notice?', 1)"

create a new migration file like 047_add_rows_in_system_settings.rb

 class AddRowsInAddSystemSettings < ActiveRecord::Migration
        def self.up
          SystemSetting.create{:name => "name1", :label => "Use notice?", :value => 1}
          SystemSetting.create{:name => "name2", :label => "Use notice?", :value => 2}
         end

        def self.down
          SystemSetting.delete_all
        end
      end

OR

while creating table

046_system_settings.rb

class AddSystemSettings < ActiveRecord::Migration
    def self.up
      create_table :system_settings do |t|
        t.string  :name
        t.string  :label
        t.text  :value
        t.string  :type
        t.integer  :position
      end

      SystemSetting.create :name => "notice", :label => "Use notice?", :value => 1
    end

    def self.down
      drop_table :system_settings
    end
  end

Ref:- http://api.rubyonrails.org/classes/ActiveRecord/Migration.html

Update: This is the right answer: https://stackoverflow.com/a/2667747/7852

---

Here's an example from ruby on rails api:

 class AddSystemSettings < ActiveRecord::Migration
    # create the table
    def self.up
      create_table :system_settings do |t|
        t.string  :name
        t.string  :label
        t.text  :value
        t.string  :type
        t.integer  :position
      end

      # populate the table
      SystemSetting.create :name => "notice", :label => "Use notice?", :value => 1
    end

    def self.down
      drop_table :system_settings
    end
  end