Database folder and migrations in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the db/migrate folder in a Rails project?

The db/migrate folder stores migration files that describe changes to the database schema, like creating or modifying tables. These files help Rails track and apply database changes in order.

beginner

What command do you run to create a new migration in Rails?

You run rails generate migration MigrationName to create a new migration file with a timestamp in the db/migrate folder.

intermediate

How do migrations help keep the database schema consistent across different environments?

Migrations record each change as a file with a timestamp. Running rails db:migrate applies all pending migrations in order, ensuring all environments have the same database structure.

intermediate

What is the role of the schema.rb file in Rails?

The schema.rb file is a snapshot of the current database structure. It is updated after migrations run and helps Rails recreate the database schema quickly without running all migrations.

intermediate

What happens if you try to run rails db:migrate but some migrations have already been applied?

Rails checks which migrations have been applied by looking at the schema_migrations table. It only runs new migrations that haven't been applied yet, so it avoids repeating changes.

Where are Rails migration files stored?

A lib/tasks

B app/models

C db/migrate

D config

Migration files live in the db/migrate folder to organize database schema changes.

What command creates a new migration file?

A rails new migration

B rails generate migration MigrationName

C rails db:create migration

D rails generate model MigrationName

Use rails generate migration followed by the name to create a migration file.

What does rails db:migrate do?

A Runs all pending migrations to update the database schema

B Deletes the database

C Creates a new Rails project

D Generates a new model

It applies all migrations that have not yet been run to update the database.

What file shows the current database schema snapshot?

A seeds.rb

B routes.rb

C database.yml

D schema.rb

schema.rb reflects the current structure of the database after migrations.

How does Rails know which migrations have already run?

A By checking the schema_migrations table in the database

B By reading the migration filenames

C By checking the config folder

D By scanning the app/models folder

Rails tracks applied migrations in the schema_migrations table to avoid rerunning them.

Explain the purpose of the db/migrate folder and how migrations work in Rails.

Think about how Rails tracks and applies database changes step-by-step.

Describe the role of the schema.rb file and how it relates to migrations.

Consider how Rails can rebuild the database structure without running all migrations again.