ruby - NOTICES for sequence after running migration in rails on postgresql Application

Question

When i run my migration in Rails application on postgresql i got following NOTICES

NOTICE:  CREATE TABLE will create implicit sequence "notification_settings_id_seq" for serial column "notification_settings.id"
NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "notification_settings_pkey" for table "notification_settings"

My migration file contains 088_create_notification_settings.rb

class CreateNotificationSettings < ActiveRecord::Migration
  def self.up
    create_table :notification_settings do |t|
      t.integer :user_id
      t.integer :notification_id
      t.boolean :notification_on
      t.boolean :outbound
    end
  end

  def self.down
    drop_table :notification_settings
  end
end

I would like to know

what this NOTICES means?

How to avoid this NOTICES?

What will be the impact of such NOTICES on the Application if not avoided?

Regards,

Salil

Answer 1

Rails (ActiveRecord to be more precise) is adding an id column to your table and making this column the primary key. For PostgreSQL, this column will have type serial. A serial column is essentially a four byte integer combined with a sequence to automatically provide auto-incrementing values.

The first notice:

NOTICE: CREATE TABLE will create implicit sequence "notification_settings_id_seq" for serial column "notification_settings.id"

is just telling you that PostgreSQL is creating a sequence behind the scenes to make the serial column function.

The second notice:

NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "notification_settings_pkey" for table "notification_settings"

is just telling you that PostgreSQL is creating an index to help implement the primary key even though you didn't explicitly ask it to.

You can just ignore these notices, they're just informational. If you want to suppress them, you can add min_messages: WARNING to the appropriate section of your database.yml.