How to Run Migration in Rails: Simple Steps to Update Your Database

To run a migration in Rails, use the rails db:migrate command in your terminal. This applies any pending database changes defined in your migration files to keep your database schema up to date.

Syntax

The basic command to run migrations in Rails is rails db:migrate. This command looks for migration files in the db/migrate folder and applies any new changes to your database schema.

Additional useful commands include:

• rails db:rollback - Reverts the last migration.
• rails db:migrate:status - Shows which migrations have been run.

bash

rails db:migrate

Example

This example shows how to create a migration to add a name column to a users table and then run the migration.

bash

rails generate migration AddNameToUsers name:string
rails db:migrate

Output

==  AddNameToUsers: migrating ===============================================
-- add_column(:users, :name, :string)
   -> 0.0012s
==  AddNameToUsers: migrated (0.0013s) ======================================

Common Pitfalls

Common mistakes when running migrations include:

• Not running rails db:migrate after creating migration files, so changes are not applied.
• Running migrations in the wrong environment (e.g., development instead of production).
• Editing migration files after they have been run, which can cause inconsistencies.
• Forgetting to check migration status with rails db:migrate:status.

bash

## Wrong way: Editing a migration after running it
# This can cause errors or inconsistent schema

# Right way: Create a new migration to change schema
rails generate migration ChangeColumnInUsers
rails db:migrate

Quick Reference

Here is a quick summary of useful migration commands:

Command	Description
rails db:migrate	Run all pending migrations
rails db:rollback	Undo the last migration
rails db:migrate:status	Show migration status
rails generate migration NAME	Create a new migration file

Key Takeaways

Run migrations with rails db:migrate to update your database schema.

Always create new migrations for changes instead of editing old ones.

Use rails db:migrate:status to check which migrations have run.

Rollback migrations safely with rails db:rollback if needed.

Ensure you run migrations in the correct environment.