Creating migrations

Rails generator

$bin/rails generate migration AddPartNumberToProducts

If the migration name is of the form “AddXXXToYYY” or “RemoveXXXFromYYY” and is followed by a list of column names and types then a migration containing the appropriate add_column and remove_column statements will be created.

Commands to create migrations

$rails generate model Product name:string description:text
$rails generate migration AddPartNumberToProducts part_number:string
$rails generate migration RemovePartNumberFromProducts part_number:string
$rails generate migration AddDetailsToProducts part_number:string price:decimal

Migrations methods:

  • add_column
  • add_index
  • change_column
  • change_table
  • create_table
  • drop_table
  • remove_column
  • remove_index
  • rename_column

Supported types

  • :binary
  • :boolean
  • :date
  • :datetime
  • :decimal
  • :float
  • :integer
  • :primary_key
  • :string
  • :text
  • :time
  • :timestamp especial type:
  • :references

To Add a column to a table

class AddPartNumberToProducts < ActiveRecord::Migration[5.0]
  def change
    add_column :products, :part_number, :string
  end
end

To remove a column from a table


class RemovePartNumberFromProducts < ActiveRecord::Migration[5.0]
  def change
    remove_column :products, :part_number, :string
  end
end

DB Rake tasks :

Execute:

rake -T db
  • db:migrate - runs migrations for the current env that have not run yet (options: VERSION=x, VERBOSE=false)
  • db:migrate:up - runs one specific migration
  • db:migrate:down - rolls back one specific migration

  • db:migrate:status - shows current migration status

  • db:create - creates the database for the current env

  • db:create:all - creates the databases for all envs

  • db:drop - drops the database for the current env

  • db:drop:all - drops the databases for all envs

  • db:rollback - rolls back the last migration (specify steps w/ STEP=n)
  • db:forward - advances the current schema version to the next one
  • db:seed - (only) runs the db/seed.rb file
  • db:schema:load - loads the schema into the current env’s database
  • db:schema:dump - dumps the current env’s schema (and seems to create the db as well)
  • db:setup - runs db:schema:load, db:seed
  • db:reset - runs db:drop db:setup, create the database, load the schema, and initialize with the seed data (use db:reset to also drop the db first)
  • db:migrate:redo - runs (db:migrate:down db:migrate:up) or (db:rollback db:migrate) depending on the specified migration
  • db:migrate:reset - runs db:drop db:create db:migrate
  • db:test:prepare - Rebuild it from scratch according to the specs defined in the development database
  • rake db:fixtures:load - Load fixtures into the current environment’s database.
  • rake db:version - Retrieves the current schema version number
$rake db:migrate VERSION=20080906120000
$rake db:rollback
$rake db:rollback STEP=3
$rake db:migrate:redo STEP=3
$rake db:reset  #drop database and recreate it
$rake db:migrate:up VERSION=20080906120000

Further information at:
http://guides.rubyonrails.org/migrations.html