Why migrations version the database in Ruby on Rails - See It in Action

Why Migrations Version the Database

📖 Scenario: You are building a simple blog application using Rails. You want to keep track of changes to your database structure over time so that your team can work together smoothly and avoid conflicts.

🎯 Goal: Understand why Rails migrations use version numbers to manage database changes and how this helps keep the database schema consistent.

📋 What You'll Learn

Create a migration file with a specific version number

Add a configuration variable to track the current schema version

Write code to apply migrations in order based on version numbers

Complete the migration setup to ensure database consistency

💡 Why This Matters

🌍 Real World

In real projects, Rails migrations help teams safely update the database structure as the app evolves.

💼 Career

Understanding migration versioning is essential for Rails developers to manage database changes and collaborate effectively.

1

Create a migration file with a version number

Create a migration file named 20240601010101_create_posts.rb with a class called CreatePosts that inherits from ActiveRecord::Migration[7.0].

Ruby on Rails

# Your migration file starts here
# Define class CreatePosts inheriting from ActiveRecord::Migration[7.0]

Need a hint?

Migration files have a timestamp prefix as their version number. The class inherits from ActiveRecord::Migration with the Rails version in brackets.

2

Add a configuration variable to track schema version

Add a variable called ActiveRecord::SchemaMigration.version and set it to the string "20240601010101" to represent the current migration version.

Ruby on Rails

class CreatePosts < ActiveRecord::Migration[7.0]
  def change
    create_table :posts do |t|
      t.string :title
      t.text :content
      t.timestamps
    end
  end
end

# Set current schema version
# Your code here

Need a hint?

The schema version is stored as a string matching the migration timestamp to track which migrations have been applied.

3

Apply migrations in order using version numbers

Write a method called apply_migrations that takes a list of migration versions and applies only those with a version greater than ActiveRecord::SchemaMigration.version.

Ruby on Rails

class CreatePosts < ActiveRecord::Migration[7.0]
  def change
    create_table :posts do |t|
      t.string :title
      t.text :content
      t.timestamps
    end
  end
end

ActiveRecord::SchemaMigration.version = "20240601010101"

# Define apply_migrations method
# Your code here

Need a hint?

Compare each migration version to the current schema version and apply only newer migrations.

4

Complete migration setup for database consistency

Add a final line to call apply_migrations with the list ["20240601010101", "20240602020202"] to simulate applying migrations in order.

Ruby on Rails

class CreatePosts  ActiveRecord::SchemaMigration.version
      # Here we would run the migration
      ActiveRecord::SchemaMigration.version = version
    end
  end
end

# Call apply_migrations with versions
# Your code here

Need a hint?

Calling apply_migrations with a list of versions simulates running migrations in the correct order.