The database schema evolves continuously. Rails migrations is a powerful and flexible way to update the schema without dropping and re-creating the database. However, all this power and flexibility can be overwhelming. Here's a handy cheatsheet for most common migration operations.| Write Software, Well
Active Record AssociationsThis guide covers the association features of Active Record.After reading this guide, you will know how to: Declare associations between Active Record models. Understand the various types of Active Record associations. Use the methods added to your models by creating associations.| Ruby on Rails Guides
Active Record BasicsThis guide is an introduction to Active Record.After reading this guide, you will know: How Active Record fits into the Model-View-Controller (MVC) paradigm. What Object Relational Mapping and Active Record patterns are and how they are used in Rails. How to use Active Record models to manipulate data stored in a relational database. Active Record schema naming conventions. The concepts of database migrations, validations, callbacks, and associations.| Ruby on Rails Guides