Running and rolling back migrations in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to run all pending migrations in Rails.

Ruby on Rails

rails db:[1]

Drag options to blanks, or click blank then click option'

Amigrate

Bseed

Crollback

Dconsole

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'rollback' instead of 'migrate' to apply migrations.

Confusing 'seed' with migration commands.

Use rails db:migrate to run all pending migrations and update the database schema.

2fill in blank

medium

Complete the code to rollback the last migration in Rails.

Ruby on Rails

rails db:[1]

Drag options to blanks, or click blank then click option'

Asetup

Bmigrate

Creset

Drollback

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'migrate' which applies migrations instead of rolling back.

Using 'reset' which drops and recreates the database.

The rails db:rollback command undoes the last migration, reverting the database schema by one step.

3fill in blank

hard

Fix the error in the command to rollback the last two migrations.

Ruby on Rails

rails db:rollback [1]2

Drag options to blanks, or click blank then click option'

A--times

B--number

CSTEP=

D--count

Attempts:

3 left

💡 Hint

Common Mistakes

Using '--count' or '--number' which are not valid options.

Omitting the option and just writing a number.

The correct option to specify how many migrations to rollback is STEP=. So the full command is rails db:rollback STEP=2.

4fill in blank

hard

Fill both blanks to create a command that resets the database and runs all migrations.

Ruby on Rails

rails db:[1] db:[2]

Drag options to blanks, or click blank then click option'

Adrop

Bmigrate

Creset

Dseed

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'drop' instead of 'reset' which does not run migrations automatically.

Using 'seed' which populates data but does not affect schema.

The rails db:reset command drops and recreates the database, then rails db:migrate runs all migrations to set up the schema.

5fill in blank

hard

Fill all three blanks to rollback the last migration, reset the database, and then migrate again.

Ruby on Rails

rails db:[1] db:[2] db:[3]

Drag options to blanks, or click blank then click option'

Adrop

Bmigrate

Creset

Drollback

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'drop' instead of 'reset' which does not run migrations automatically.

Mixing the order of commands.

First, rails db:rollback undoes the last migration, then rails db:reset drops and recreates the database, and finally rails db:migrate runs all migrations again.

Practice

1. What does running a migration in Rails do?

easy

A. Applies changes to the database schema step-by-step

B. Deletes the entire database

C. Creates a backup of the database

D. Restarts the Rails server

Solution

1. Step 1: Understand migration purpose

   Migrations are designed to change the database schema in a controlled way.

2. Step 2: Identify what running migration does

   Running a migration applies these schema changes step-by-step to the database.

3. Final Answer:

   Applies changes to the database schema step-by-step -> Option A

4. Quick Check:

   Running migration = apply schema changes [OK]

Hint: Running migration updates database schema stepwise [OK]

Common Mistakes:

• Thinking it deletes the database
• Confusing migration with backup
• Assuming it restarts the server

2. Which command correctly rolls back the last migration in Rails?

easy

A. rails db:reset

B. rails db:rollback

C. rails db:migrate:down

D. rails db:rollback STEP=2

Solution

1. Step 1: Recall rollback command syntax

   The basic command to undo the last migration is rails db:rollback.

2. Step 2: Analyze other options

   rails db:migrate:down requires specifying a version, rails db:reset resets the whole database, and rails db:rollback STEP=2 rolls back two steps, not one.

3. Final Answer:

   rails db:rollback -> Option B

4. Quick Check:

   Rollback last migration = rails db:rollback [OK]

Hint: Rollback last migration uses rails db:rollback [OK]

Common Mistakes:

• Using db:reset which resets entire DB
• Using rollback with STEP=2 to undo one migration
• Confusing migrate:down without version

3. Given these commands run in order:
rails db:migrate
rails db:migrate
rails db:rollback STEP=2
What is the state of the database migrations?

medium

A. Only the first migration is applied

B. All migrations are applied

C. No migrations are applied

D. Only the last migration is applied

Solution

1. Step 1: Understand the commands run

   Two migrations are applied by running rails db:migrate twice, then rollback with STEP=2 undoes both.

2. Step 2: Determine final migration state

   Rolling back two steps removes both migrations, so no migrations remain applied.

3. Final Answer:

   No migrations are applied -> Option C

4. Quick Check:

   Rollback STEP=2 undoes two migrations [OK]

Hint: Rollback STEP=2 undoes last two migrations [OK]

Common Mistakes:

• Assuming rollback STEP=2 only undoes one migration
• Thinking migrations remain applied after rollback
• Confusing migrate command effects

4. You run rails db:rollback STEP=3 but get an error saying there are not enough migrations to rollback. What is the likely cause?

medium

A. The STEP option is not supported

B. Rollback only works with STEP=1

C. You need to restart the Rails server first

D. There are fewer than 3 migrations applied

Solution

1. Step 1: Understand rollback STEP behavior

   Rollback with STEP=n tries to undo n migrations if they exist.

2. Step 2: Analyze error cause

   If fewer than 3 migrations are applied, rollback STEP=3 fails because it can't undo more than exist.

3. Final Answer:

   There are fewer than 3 migrations applied -> Option D

4. Quick Check:

   Rollback STEP=n needs at least n migrations applied [OK]

Hint: Rollback STEP=n requires n migrations applied [OK]

Common Mistakes:

• Thinking STEP option is unsupported
• Believing server restart fixes rollback errors
• Assuming rollback only works with STEP=1

5. You have applied 5 migrations. You want to undo the last 3 migrations and then reapply them one by one to test changes. Which sequence of commands achieves this?

hard

A. rails db:rollback STEP=3, then rails db:migrate three times

B. rails db:rollback STEP=3, then rails db:migrate once

C. rails db:migrate:reset, then rails db:migrate

D. rails db:rollback, then rails db:migrate STEP=3

Solution

1. Step 1: Undo last 3 migrations

   Use rails db:rollback STEP=3 to undo the last three migrations at once.

2. Step 2: Reapply migrations one by one

   Run rails db:migrate three times to apply each migration individually.

3. Final Answer:

   rails db:rollback STEP=3, then rails db:migrate three times -> Option A

4. Quick Check:

   Rollback STEP=3 + migrate x3 reapplies migrations [OK]

Hint: Rollback STEP=3 then migrate repeatedly reapplies changes [OK]

Common Mistakes:

• Using migrate once after rollback STEP=3
• Resetting database instead of rolling back
• Trying migrate with STEP option (not valid)