Database folder and migrations in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to generate a new migration file in Rails.

Ruby on Rails

rails generate [1] CreateUsers

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

Amodel

Bcontroller

Cmigration

Dscaffold

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'model' instead of 'migration' creates a model and migration, not just migration.

Using 'controller' or 'scaffold' generates other files, not just migrations.

In Rails, to create a new migration file, you use rails generate migration.

2fill in blank

medium

Complete the migration method to add a new column named 'age' of type integer to the 'users' table.

Ruby on Rails

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

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

Astring

Bdate

Cboolean

Dinteger

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'string' for numeric data.

Using 'boolean' which only stores true or false.

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

3fill in blank

hard

Fix the error in the migration method to create a 'products' table with a 'name' column of type string.

Ruby on Rails

def change
  create_table :products do |[1]|
    [1].string :name
  end
end

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

Atable

Bt

Ccolumn

Dp

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'table' or 'column' which are not standard block variables.

Using 'p' which is uncommon and confusing.

The block variable for create_table is conventionally t, used to define columns.

4fill in blank

hard

Fill both blanks to write a migration that removes the 'age' column from the 'users' table.

Ruby on Rails

def change
  [1]_column :users, :age, :[2]
end

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

Aremove

Binteger

Cstring

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'add_column' instead of 'remove_column'.

Using wrong column type like 'string' for 'age'.

To remove a column, use remove_column with the table name, column name, and column type.

5fill in blank

hard

Fill all three blanks to write a migration that creates a 'posts' table with a 'title' string column and a 'published' boolean column.

Ruby on Rails

def change
  create_table :posts do |[1]|
    [1].[2] :title
    [1].[3] :published
  end
end

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

At

Bstring

Cboolean

Dp

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong block variable like 'p'.

Mixing up column types like using 'boolean' for 'title'.

The block variable is 't'. Use t.string for 'title' and t.boolean for 'published'.

Practice

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

easy

A. To store migration files that change the database structure step-by-step

B. To hold all the Ruby model files for the application

C. To keep the application configuration files

D. To store static assets like images and stylesheets

Solution

1. Step 1: Understand the role of the db/migrate folder

   This folder contains migration files that describe changes to the database schema over time.

2. Step 2: Differentiate from other folders

   Model files are in app/models, configs in config, and assets in app/assets.

3. Final Answer:

   To store migration files that change the database structure step-by-step -> Option A

4. Quick Check:

   Migration files = db/migrate folder [OK]

Hint: Migrations live in db/migrate to track database changes [OK]

Common Mistakes:

• Confusing migrations with model files
• Thinking assets or configs are in db/migrate
• Assuming db/migrate holds seed data

2. Which command correctly generates a new migration file in Rails?

easy

A. rails new migration AddAgeToUsers age:integer

B. rails generate migration AddAgeToUsers age:integer

C. rails create migration AddAgeToUsers age:integer

D. rails make migration AddAgeToUsers age:integer

Solution

1. Step 1: Recall the Rails command for generating migrations

   The correct command is rails generate migration followed by the migration name and fields.

2. Step 2: Check the options for correct syntax

   Only rails generate migration AddAgeToUsers age:integer uses the exact Rails command syntax for migration generation.

3. Final Answer:

   rails generate migration AddAgeToUsers age:integer -> Option B

4. Quick Check:

   Use rails generate migration to create migrations [OK]

Hint: Use 'rails generate migration' to create migration files [OK]

Common Mistakes:

• Using 'rails create' instead of 'rails generate'
• Confusing 'rails new' with migration commands
• Using 'rails make' which is invalid

3. Given this migration file content:

class CreateBooks < ActiveRecord::Migration[7.0]
  def change
    create_table :books do |t|
      t.string :title
      t.integer :pages
      t.timestamps
    end
  end
end

What will happen when you run rails db:migrate?

medium

A. Nothing happens because migrations only update existing tables

B. An error occurs because the migration syntax is wrong

C. The existing 'books' table will be deleted

D. A new table named 'books' with columns 'title', 'pages', and timestamps will be created

Solution

1. Step 1: Analyze the migration code

   The migration defines creating a new table called 'books' with columns 'title' (string), 'pages' (integer), and timestamps.

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

   It runs pending migrations, applying the changes to the database schema, here creating the 'books' table.

3. Final Answer:

   A new table named 'books' with columns 'title', 'pages', and timestamps will be created -> Option D

4. Quick Check:

   Create table migration runs successfully [OK]

Hint: Create_table migrations add new tables when migrated [OK]

Common Mistakes:

• Thinking migration deletes tables
• Assuming syntax error without checking code
• Believing migrations only update, not create

4. You wrote this migration:

class AddEmailToUsers < ActiveRecord::Migration
  def change
    add_column :users, :email, :string
  end
end

But running rails db:migrate gives an error: undefined method 'add_column'. What is the likely cause?

medium

A. The migration class should inherit from ActiveRecord::Migration[7.0] but it does

B. The migration file is missing the def change method

C. The migration class is missing the version number in inheritance

D. The migration file name does not match the class name

Solution

1. Step 1: Check the migration inheritance

   Rails 7 requires specifying the migration version in the class inheritance, e.g., ActiveRecord::Migration[7.0].

2. Step 2: Identify the error cause

   If the version is missing or incorrect, Rails may not recognize migration methods like add_column, causing the error.

3. Final Answer:

   The migration class is missing the version number in inheritance -> Option C

4. Quick Check:

   Migration version number required for method recognition [OK]

Hint: Always specify migration version in class inheritance [OK]

Common Mistakes:

• Ignoring migration version in class inheritance
• Assuming method missing means syntax error
• Not matching file name and class name

5. You want to rename a column username to login in the users table using a migration. Which migration code correctly does this?

hard

A. def change
rename_column :users, :username, :login
end

B. def change
change_column :users, :username, :login
end

C. def change
remove_column :users, :username
add_column :users, :login, :string
end

D. def change
rename_table :users, :login
end

Solution

1. Step 1: Understand the goal

   You want to rename a column, not change its type or remove and add a new one.

2. Step 2: Identify the correct migration method

   rename_column changes a column's name safely without losing data.

3. Step 3: Check options

   def change rename_column :users, :username, :login end uses rename_column :users, :username, :login, which is correct. def change change_column :users, :username, :login end wrongly uses change_column which changes type, not name. def change remove_column :users, :username add_column :users, :login, :string end removes and adds columns, which is risky. def change rename_table :users, :login end renames the whole table, not a column.

4. Final Answer:

   def change rename_column :users, :username, :login end -> Option A

5. Quick Check:

   Use rename_column to rename columns safely [OK]

Hint: Use rename_column to rename columns without data loss [OK]

Common Mistakes:

• Using change_column to rename instead of change type
• Removing and adding columns loses data
• Confusing rename_table with rename_column