Running and rolling back migrations in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens after running rails db:migrate?

You run rails db:migrate in your Rails project. What is the immediate effect on your database?

A All migrations are deleted from the migrations folder to prevent rerunning.

B The database is reset to its initial empty state, removing all tables.

C The Rails server automatically restarts to apply migration changes.

D The database schema is updated to include all pending migrations, and a record is added to the schema_migrations table.

💡 Hint

Think about what migrations do to the database structure and how Rails tracks them.

Running rails db:migrate applies all pending migrations to update the database schema. Rails records which migrations have run in the schema_migrations table to avoid rerunning them.

❓ state_output

intermediate

What is the state of the database after rails db:rollback?

After running rails db:migrate to apply three migrations, you run rails db:rollback. What is the state of the database schema?

A The last applied migration is reversed, so the database schema reflects only the first two migrations.

B All migrations are reversed, and the database schema is empty.

C The database schema remains unchanged because rollback only affects migration files.

D The first migration is reversed, but the last two remain applied.

💡 Hint

Rollback undoes migrations one step at a time, starting from the most recent.

rails db:rollback reverses the last migration that was applied, updating the database schema accordingly. It does not undo all migrations at once.

📝 Syntax

advanced

Which command rolls back the last two migrations?

You want to undo the last two migrations you applied. Which command correctly does this?

A rails db:migrate:down VERSION=2

B rails db:rollback --count=2

C rails db:rollback STEP=2

D rails db:reset STEP=2

💡 Hint

Look for the option that specifies how many steps to rollback.

The STEP option tells Rails how many migrations to rollback. rails db:rollback STEP=2 rolls back the last two migrations.

🔧 Debug

advanced

Why does rails db:rollback fail with 'No migrations to rollback'?

You run rails db:rollback but get the error 'No migrations to rollback'. What is the most likely reason?

A There are no migrations applied yet, so nothing to rollback.

B The migration files are missing from the project folder.

C The database connection is not established.

D The Rails version does not support rollback commands.

💡 Hint

Rollback only works if migrations have been applied before.

If no migrations have been applied, Rails cannot rollback anything and shows this error.

🧠 Conceptual

expert

What is the effect of rails db:migrate:redo?

You run rails db:migrate:redo. What does this command do to your database schema?

A It deletes the last migration file and updates the schema accordingly.

B It rolls back the last migration and then reapplies it, effectively refreshing the last migration.

C It applies all pending migrations without rolling back any.

D It resets the entire database and reapplies all migrations from scratch.

💡 Hint

Think about what 'redo' means in terms of undoing and reapplying.

rails db:migrate:redo rolls back the last migration and then runs it again. This is useful for testing or fixing the last migration.