cheat sheets.

--- migrations version 171	Sun Mar 02 22:28:54 +0000 2008
+++ migrations version 172	Wed Jun 18 20:38:00 +0000 2008
@@ -1,82 +1,84 @@
 Methods:
   create_table(name, options)
   drop_table(name)
   rename_table(old_name, new_name)
   add_column(table_name, column_name, type, options)
   rename_column(table_name, column_name, new_column_name)
   change_column(table_name, column_name, type, options)
   remove_column(table_name, column_name)
   add_index(table_name, column_name, index_type)
   remove_index(table_name, column_name)
 
 Available Column Types:
   * integer
   * float
   * datetime
   * date
   * timestamp
   * time
   * text
   * string
   * binary
   * boolean
   * decimal :precision, :scale
 
 Valid Column Options:
   * limit
   * null (i.e. ":null => false" implies NOT NULL)
   * default (to specify default values)
   * :decimal, :precision => 8, :scale => 3
   
 Rake Tasks:
   rake db:schema:dump: run after you create a model to capture the schema.rb
   rake db:schema:import: import the schema file into the current database (on
   error, check if your schema.rb has ":force => true" on the create table
   statements
   ./script/generate migration MigrationName: generate a new migration with a new
   'highest' version (run './script/generate migration' for this info at your
   fingertips)
   rake db:migrate: migrate your current database to the most recent version
   rake db:migrate VERSION=5: migrate your current database to a specific version
   (in this case, version 5)
+  rake db:rollback: migrate down one migration
+  rake db:rollback STEP=3: migrate down three migrations
   rake db:migrate RAILS_ENV=production: migrate your production database
 
 SQL:
   Queries can be executed directly:
   execute 'ALTER TABLE researchers ADD CONSTRAINT fk_researchers_departments
   FOREIGN KEY ( department_id ) REFERENCES departments( id )'
   
 Example Migration:
   class UpdateUsersAndCreateProducts < ActiveRecord::Migration
     def self.up
       rename_column "users", "password", "hashed_password" 
       remove_column "users", "email" 
 
        User.reset_column_information
        User.find(:all).each{|u| #do something with u}
 
       create_table "products", :force => true do |t|
           t.column "name", :text
           t.column "description", :text
           t.column "price", :decimal, :precision => 9, :scale => 2
       end
 
       #the rails 2.0 way:
       create_table :people do |t|
         t.integer :account_id
         t.string  :first_name, :last_name, :null => false
         t.text    :description
         t.timestamps
       end
     end
 
     def self.down
       rename_column "users", "hashed_password", "password" 
       add_column "users", "email", :string
       drop_table "products" 
     end
   end
 
 Find Highest version:
   script/runner "puts ActiveRecord::Migrator.current_version"