Creating migrations in Ruby on Rails

Introduction

Migrations help you change your database structure safely and easily. They keep track of changes so your app can grow without losing data.

When you want to add a new table to your database.

When you need to add or remove columns from an existing table.

When you want to rename or change the type of a column.

When you want to delete a table you no longer need.

When you want to share database changes with your team.

Syntax

Ruby on Rails

rails generate migration MigrationName [field:type field:type ...]

MigrationName should describe the change, like AddEmailToUsers or CreateProducts.

You can add fields with their types right in the command to create columns.

Examples

This creates a migration to make a users table with name and age columns.

Ruby on Rails

rails generate migration CreateUsers name:string age:integer

This adds an email column to the existing users table.

Ruby on Rails

rails generate migration AddEmailToUsers email:string

This removes the age column from the users table.

Ruby on Rails

rails generate migration RemoveAgeFromUsers age:integer

Sample Program

This example creates a migration file to add a books table with title, author, and published_year columns. Running rake db:migrate applies the change to the database.

Ruby on Rails

rails generate migration CreateBooks title:string author:string published_year:integer

# Then run:
rake db:migrate

Important Notes

Always write clear migration names to understand what changes they make.

Run rake db:migrate after creating migrations to apply changes.

You can rollback migrations if needed using rake db:rollback.

Summary

Migrations let you change your database structure step-by-step.

Use rails generate migration with a descriptive name and optional fields.

Run rake db:migrate to apply your migration changes.