Rails Migrations Cheat sheet

gistfile1.rb

# Migration generator shortcuts.
# rails generate migration MyNewMigration
# rails generate migration add_fieldname_to_tablename fieldname:string
# rails generate model Product name:string description:text
# The set of available column types [:string, :text, :integer, :float, :decimal, :datetime, :timestamp, :time, :date, :binary, :boolean]


# A migration is a subclass of ActiveRecord::Migration.  You must implement the "up" and "down" (revert) methods.

# These are the handy methods available to a Migration:
create_table
change_table
drop_table
add_column
change_column
rename_column
remove_column
add_index
remove_index
execute  # (use this method to compose and execute raw sql -- note that foreign key constraints aren't included in the functions above, so that's something you'd do with 'execute')

# See http://api.rubyonrails.org/classes/ActiveRecord/Migration.html for the params for these functions.

# Here's how the add_column function works, note the applicable types for columns.
# add_column(table_name, column_name, type, options): Adds a new column to the table called table_name named column_name specified to be one of the following types: :string, :text, :integer, :float, :decimal, :datetime, :timestamp, :time, :date, :binary, :boolean. A default value can be specified by passing an options hash like { :default => 11 }. Other options include :limit and :null (e.g. { :limit => 50, :null => false }) 

# If your migration can't be reverted, throw the ActiveRecord::IrreversibleMigration exception in your "down" method.

# If you want to both add a new column and populate/use that column in the same migration, you have to use the reset_column_information function.  See below:

class AddPeopleSalary < ActiveRecord::Migration
  def self.up
    add_column :people, :salary, :integer
    Person.reset_column_information
    Person.find(:all).each do |p|
      p.update_attribute :salary, SalaryCalculator.compute(p)
    end
  end
end