Handling Migrations and Database Schema

Tutorial 2 of 5

Introduction

This tutorial aims to guide you through the process of handling migrations and managing your database schema in Rails. By the end of this tutorial, you should be able to understand and use Rails migrations to create, modify, and manage different versions of your database schema effectively.

You will learn:
- What Rails Migrations are and why they're important.
- How to create, modify and rollback migrations.
- Managing your database schema using Rails Migrations.

Prerequisites:
- Basic knowledge of Ruby on Rails.
- A Rails application set up on your local machine.

Step-by-Step Guide

Rails migrations are a convenient way to alter your database schema over time in a consistent and easy way. They use a Ruby DSL so that you don't have to write SQL by hand, allowing your schema and changes to be database independent.

Creating a Migration:
Migrations are typically created with the rails generate command followed by migration and the name of your migration.

rails generate migration AddPartNumberToProducts part_number:string

This will create a migration file in the db/migrate directory.

Running Migrations:
To apply the changes defined in the migration file to your database, you run the migrations using the rails db:migrate command.

Rolling Back Migrations:
Migrations can also be rolled back using the rails db:rollback command, which will undo the last migration command.

Code Examples

Example 1: Creating a Migration

class AddPartNumberToProducts < ActiveRecord::Migration[6.0]
  def change
    add_column :products, :part_number, :string
  end
end

This migration adds a new column, part_number, to the products table.

Example 2: Modifying a Migration

class ChangePartNumberFormatInProducts < ActiveRecord::Migration[6.0]
  def up
    change_column :products, :part_number, :integer
  end

  def down
    change_column :products, :part_number, :string
  end
end

This migration changes the type of the part_number column from string to integer.

Summary

In this tutorial, we've covered how to create, modify, and manage your database schema using Rails migrations. We've also learned how to roll back changes and why migrations are essential for database schema management.

Practice Exercises

Create a migration to add a reviews table with content (text), user_id (integer), and product_id (integer).
Modify the reviews table to change the content column into a string type.
Roll back the last migration you applied.