Adding and removing columns in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a new column named age of type integer to the users table.

Ruby on Rails

class AddAgeToUsers < ActiveRecord::Migration[6.1]
  def change
    add_column :users, :age, :[1]
  end
end

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

Astring

Binteger

Cdate

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string type for numeric data.

Forgetting to specify the column type.

The add_column method requires the table name, column name, and the column type. Here, integer is the correct type for the age column.

2fill in blank

medium

Complete the code to remove the email column from the customers table.

Ruby on Rails

class RemoveEmailFromCustomers < ActiveRecord::Migration[6.1]
  def change
    remove_column :customers, :[1]
  end
end

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

Aname

Bphone

Caddress

Demail

Attempts:

3 left

💡 Hint

Common Mistakes

Removing the wrong column by mistake.

Forgetting to specify the column name.

The remove_column method needs the table name and the column name to remove. Here, the column to remove is email.

3fill in blank

hard

Fix the error in the migration code to add a published_at column of type datetime to the posts table.

Ruby on Rails

class AddPublishedAtToPosts < ActiveRecord::Migration[6.1]
  def change
    add_column :posts, :published_at, :[1]
  end
end

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

Ainteger

Bstring

Cdatetime

Dboolean

Attempts:

3 left

💡 Hint

Common Mistakes

Using string instead of datetime.

Using integer or boolean incorrectly.

The published_at column should store date and time, so the correct type is datetime.

4fill in blank

hard

Fill both blanks to add a price column of type decimal with precision 8 and scale 2 to the products table.

Ruby on Rails

class AddPriceToProducts < ActiveRecord::Migration[6.1]
  def change
    add_column :products, :price, :[1], precision: [2], scale: 2
  end
end

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

Adecimal

Binteger

C8

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using integer instead of decimal.

Setting wrong precision value.

The price column should be decimal type with precision 8 and scale 2 to store prices accurately.

5fill in blank

hard

Fill all three blanks to create a migration that removes the description column of type text from the items table.

Ruby on Rails

class RemoveDescriptionFromItems < ActiveRecord::Migration[6.1]
  def change
    remove_column :items, :[1], :[2], null: [3]
  end
end

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

Aname

Bdescription

Ctext

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the column type when removing a column.

Setting incorrect null constraint.

To remove the description column of type text, specify the column name, type, and null: false if the column was not nullable.

Practice

1. What is the primary purpose of adding a column in a Rails migration?

easy

A. To rename an existing table

B. To delete old data from the database

C. To create a new database table

D. To store new types of data in an existing database table

Solution

1. Step 1: Understand what adding a column means

   Adding a column means extending an existing table to hold more data fields.

2. Step 2: Identify the purpose of adding columns in Rails migrations

   It allows storing new types of data without creating a new table or deleting data.

3. Final Answer:

   To store new types of data in an existing database table -> Option D

4. Quick Check:

   Adding columns = storing new data [OK]

Hint: Adding columns means expanding tables to hold new data [OK]

Common Mistakes:

• Confusing adding columns with creating tables
• Thinking adding columns deletes data
• Mixing up adding columns with renaming tables

2. Which of the following is the correct syntax to add a column named age of type integer to the users table in a Rails migration?

easy

A. add_column :users, :age, :integer

B. add_column users, age, integer

C. add_column(:users, :age, integer)

D. add_column(:users, age, :integer)

Solution

1. Step 1: Recall the correct method signature for adding a column

   The method is add_column(table_name, column_name, type) with symbols for names.

2. Step 2: Check each option for correct syntax

   add_column :users, :age, :integer uses symbols and correct commas: add_column :users, :age, :integer.

3. Final Answer:

   add_column :users, :age, :integer -> Option A

4. Quick Check:

   Correct syntax uses symbols and commas [OK]

Hint: Use symbols and commas: add_column :table, :column, :type [OK]

Common Mistakes:

• Omitting colons before symbols
• Using parentheses incorrectly
• Missing commas between arguments

3. Given this migration code:

class AddNicknameToUsers < ActiveRecord::Migration[7.0]
  def change
    add_column :users, :nickname, :string
  end
end

What will happen after running rails db:migrate?

medium

A. An error will occur because the migration is missing a remove_column

B. The users table will be deleted

C. A new column 'nickname' of type string will be added to the users table

D. The nickname column will be removed from the users table

Solution

1. Step 1: Understand the migration code

   The migration adds a string column called nickname to the users table inside the change method.

2. Step 2: Know what rails db:migrate does

   It applies the change method, adding the new column to the database table.

3. Final Answer:

   A new column 'nickname' of type string will be added to the users table -> Option C

4. Quick Check:

   add_column in change adds the column [OK]

Hint: add_column inside change adds the column on migrate [OK]

Common Mistakes:

• Thinking remove_column is required to add columns
• Confusing add_column with deleting tables
• Assuming migration deletes columns by default

4. You wrote this migration to remove the birthdate column from users:

class RemoveBirthdateFromUsers < ActiveRecord::Migration[7.0]
  def change
    remove_column :users, :birthdate
  end
end

When running rails db:migrate, you get an error. What is the likely cause?

medium

A. remove_column requires the column type as a third argument in change method

B. remove_column cannot be used inside change method

C. The migration class name is incorrect

D. You must use add_column to remove a column

Solution

1. Step 1: Recall remove_column syntax in change method

   When using remove_column inside change, you must provide the column type as the third argument.

2. Step 2: Check the migration code

   The code misses the column type, causing an error during migration.

3. Final Answer:

   remove_column requires the column type as a third argument in change method -> Option A

4. Quick Check:

   remove_column in change needs column type [OK]

Hint: Provide column type when removing columns in change method [OK]

Common Mistakes:

• Omitting column type argument
• Trying to remove columns with add_column
• Misnaming migration class

5. You want to add a status column to orders with default value 'pending' and then remove the old_status column safely. Which migration code correctly does this?

hard

A. def change
add_column :orders, :status, :string
remove_column :orders, :old_status
end

B. def change
add_column :orders, :status, :string, default: 'pending'
remove_column :orders, :old_status, :string
end

C. def change
add_column :orders, :status, :string, default: 'pending'
remove_column :orders, :old_status
end

D. def up
add_column :orders, :status, :string, default: 'pending'
remove_column :orders, :old_status, :string
end
def down
remove_column :orders, :status
add_column :orders, :old_status, :string
end

Solution

1. Step 1: Understand adding with default and removing columns safely

   Adding a column with default works in change. Removing a column in change requires the type for reversibility.

2. Step 2: Analyze options for correctness and safety

   def change add_column :orders, :status, :string, default: 'pending' remove_column :orders, :old_status, :string end uses def change add_column :orders, :status, :string, default: 'pending' remove_column :orders, :old_status, :string end with default on add and type on remove for safe migration and rollback.

3. Final Answer:

   def change add_column :orders, :status, :string, default: 'pending' remove_column :orders, :old_status, :string end -> Option B

4. Quick Check:

   change method with type for remove and default for add [OK]

Hint: Use change with column type for safe remove_column [OK]

Common Mistakes:

• Omitting column type when removing
• Not providing default value when needed
• Using change method without rollback safety