Creating migrations in Ruby on Rails - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to generate a new migration named AddAgeToUsers.

Ruby on Rails

rails generate [1] AddAgeToUsers

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

Amigration

Bscaffold

Ccontroller

Dmodel

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'model' or 'controller' instead of 'migration'.

Forgetting to specify the migration name.

The rails generate migration command creates a new migration file.

2fill in blank

medium

Complete the migration method to add an integer column named age to users table.

Ruby on Rails

def change
  add_column :users, :age, [1]
end

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

A:boolean

B:string

C:date

D:integer

Attempts:

3 left

💡 Hint

Common Mistakes

Using :string or :boolean instead of :integer.

Omitting the column type.

The add_column method needs the column type. Here, :integer is correct for age.

3fill in blank

hard

Fix the error in the migration to remove the age column from users table.

Ruby on Rails

def change
  [1] :users, :age
end

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

Aremove_column

Bchange_column

Crename_column

Dadd_column

Attempts:

3 left

💡 Hint

Common Mistakes

Using add_column instead of remove_column.

Using rename_column or change_column incorrectly.

To remove a column, use remove_column method.

4fill in blank

hard

Fill both blanks to create a migration that adds a string column called email to users table.

Ruby on Rails

def change
  [1] :users, :email, [2]
end

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

Aadd_column

B:integer

C:string

Dremove_column

Attempts:

3 left

💡 Hint

Common Mistakes

Using remove_column instead of add_column.

Using :integer instead of :string for email.

Use add_column to add a column, and specify :string as the type for email.

5fill in blank

hard

Fill all three blanks to create a migration that renames the column username to login in users table.

Ruby on Rails

def change
  [1] :users, [2], [3]
end

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

Aadd_column

B:username

C:login

Drename_column

Attempts:

3 left

💡 Hint

Common Mistakes

Using add_column instead of rename_column.

Swapping old and new column names.

Use rename_column with the old column name :username and the new name :login.

Practice

1. What is the main purpose of a migration in Rails?

easy

A. To change the database structure step-by-step

B. To write application business logic

C. To style the user interface

D. To manage user sessions

Solution

1. Step 1: Understand what migrations do

   Migrations are used to modify the database schema in a controlled way.

2. Step 2: Identify the correct purpose

   Changing database structure step-by-step matches the role of migrations.

3. Final Answer:

   To change the database structure step-by-step -> Option A

4. Quick Check:

   Migrations = Change database structure [OK]

Hint: Migrations change database structure, not app logic or UI [OK]

Common Mistakes:

• Confusing migrations with application code
• Thinking migrations handle UI or sessions

2. Which command correctly generates a migration to add a title column of type string to the posts table?

easy

A. rails generate migration AddColumn posts title:string

B. rails generate migration CreatePosts title:string

C. rails generate migration AddTitleToPosts title:string

D. rails generate migration AddTitle posts string

Solution

1. Step 1: Identify the correct migration naming pattern

   Adding a column uses 'AddColumnNameToTableName' format, here 'AddTitleToPosts'.

2. Step 2: Check the command syntax

   The correct syntax is 'rails generate migration AddTitleToPosts title:string'.

3. Final Answer:

   rails generate migration AddTitleToPosts title:string -> Option C

4. Quick Check:

   Correct migration command = rails generate migration AddTitleToPosts title:string [OK]

Hint: Use 'AddColumnToTable' naming with column:type [OK]

Common Mistakes:

• Using 'CreatePosts' instead of 'AddTitleToPosts'
• Wrong order or missing 'To' in migration name
• Incorrect column type syntax

3. Given this migration code:

class AddAgeToUsers < ActiveRecord::Migration[7.0]
  def change
    add_column :users, :age, :integer
  end
end

What happens after running rails db:migrate?

medium

A. Raises a syntax error due to missing migration version

B. Removes the 'age' column from the 'users' table

C. Creates a new 'users' table with an 'age' column

D. Adds an integer column named 'age' to the 'users' table

Solution

1. Step 1: Analyze the migration class

   The migration inherits from ActiveRecord::Migration[7.0] and defines a change method adding a column.

2. Step 2: Understand the add_column method

   It adds an integer column 'age' to the existing 'users' table.

3. Final Answer:

   Adds an integer column named 'age' to the 'users' table -> Option D

4. Quick Check:

   add_column adds column = Adds an integer column named 'age' to the 'users' table [OK]

Hint: add_column adds a new column to existing table [OK]

Common Mistakes:

• Confusing add_column with remove_column
• Thinking it creates a new table
• Missing migration version causes error (not here)

4. You wrote this migration:

class AddEmailToUsers < ActiveRecord::Migration[7.0]
  def change
    add_column :users, :email
  end
end

What is the problem when running rails db:migrate?

medium

A. Syntax error due to missing 'def up' method

B. Missing column type for 'email' causes an error

C. Migration runs successfully without issues

D. Table 'users' does not exist error

Solution

1. Step 1: Check add_column method usage

   add_column requires three arguments: table name, column name, and column type.

2. Step 2: Identify missing argument

   The migration misses the column type for 'email', causing an error.

3. Final Answer:

   Missing column type for 'email' causes an error -> Option B

4. Quick Check:

   add_column needs type argument [OK]

Hint: Always specify column type with add_column [OK]

Common Mistakes:

• Omitting column type argument
• Assuming migration runs without errors
• Confusing change method with up/down methods

5. You want to create a migration that renames the column username to login in the accounts table. Which migration code correctly does this?

hard

A. class RenameUsernameToLogin < ActiveRecord::Migration[7.0]
def change
rename_column :accounts, :username, :login
end
end

B. class RenameUsernameToLogin < ActiveRecord::Migration[7.0]
def change
change_column :accounts, :username, :login
end
end

C. class RenameUsernameToLogin < ActiveRecord::Migration[7.0]
def change
rename_table :username, :login
end
end

D. class RenameUsernameToLogin < ActiveRecord::Migration[7.0]
def change
remove_column :accounts, :username
add_column :accounts, :login, :string
end
end

Solution

1. Step 1: Identify the correct method to rename a column

   Rails provides rename_column to rename columns in a table.

2. Step 2: Check each option's method

   class RenameUsernameToLogin < ActiveRecord::Migration[7.0] def change rename_column :accounts, :username, :login end end uses rename_column correctly; class RenameUsernameToLogin < ActiveRecord::Migration[7.0] def change change_column :accounts, :username, :login end end wrongly uses change_column; class RenameUsernameToLogin < ActiveRecord::Migration[7.0] def change rename_table :username, :login end end tries to rename tables; class RenameUsernameToLogin < ActiveRecord::Migration[7.0] def change remove_column :accounts, :username add_column :accounts, :login, :string end end removes and adds columns instead of renaming.

3. Final Answer:

   Use rename_column :accounts, :username, :login in change method -> Option A

4. Quick Check:

   rename_column renames columns = class RenameUsernameToLogin < ActiveRecord::Migration[7.0] def change rename_column :accounts, :username, :login end end [OK]

Hint: Use rename_column to rename columns, not change_column [OK]

Common Mistakes:

• Using change_column instead of rename_column
• Trying to rename tables instead of columns
• Removing and adding columns instead of renaming