Column types and attributes in Ruby on Rails - Mini Project: Build & Apply

Column types and attributes

📖 Scenario: You are building a simple Rails application to manage a library's book collection. Each book has a title, author, number of pages, and a flag indicating if it is currently available for borrowing.

🎯 Goal: Create a Rails migration to define a books table with appropriate column types and attributes for the book's title, author, pages, and availability.

📋 What You'll Learn

Create a migration file defining a books table

Add a title column as a string

Add an author column as a string

Add a pages column as an integer

Add an available column as a boolean with a default value of true

💡 Why This Matters

🌍 Real World

Defining database tables with correct column types and attributes is essential for storing and managing data in Rails applications.

💼 Career

Rails developers frequently write migrations to create and modify database schemas, ensuring data integrity and application functionality.

1

Create the books table

Write a migration class called CreateBooks inheriting from ActiveRecord::Migration[7.0]. Inside the change method, create a table named books.

Ruby on Rails

class CreateBooks < ActiveRecord::Migration[7.0]
  def change
    # Your code here
  end
end

Hint

Use create_table :books do |t| ... end inside the change method.

2

Add title and author columns

Inside the create_table :books block, add a title column and an author column, both with the type string.

Ruby on Rails

class CreateBooks < ActiveRecord::Migration[7.0]
  def change
    create_table :books do |t|
      # Your code here
    end
  end
end

Hint

Use t.string :title and t.string :author inside the block.

3

Add pages and available columns

Add a pages column with type integer and an available column with type boolean and a default value of true inside the create_table block.

Ruby on Rails

class CreateBooks < ActiveRecord::Migration[7.0]
  def change
    create_table :books do |t|
      t.string :title
      t.string :author
      # Your code here
    end
  end
end

Hint

Use t.integer :pages and t.boolean :available, default: true.

4

Add timestamps

Add timestamps to the books table inside the create_table block to track creation and update times.

Ruby on Rails

class CreateBooks < ActiveRecord::Migration[7.0]
  def change
    create_table :books do |t|
      t.string :title
      t.string :author
      t.integer :pages
      t.boolean :available, default: true
      # Your code here
    end
  end
end

Hint

Use t.timestamps inside the block to add created_at and updated_at columns.

Practice

1. Which column type in Rails is best suited to store true or false values?

easy

A. boolean

B. string

C. integer

D. text

Solution

1. Step 1: Understand column types for data

   Boolean columns store true or false values, perfect for yes/no data.

2. Step 2: Compare with other types

   String and text store text, integer stores numbers, so they don't fit true/false data.

3. Final Answer:

   boolean -> Option A

4. Quick Check:

   Boolean = true/false [OK]

Hint: True/false data uses boolean type in Rails [OK]

Common Mistakes:

• Choosing string or text for true/false data
• Using integer to represent boolean values
• Confusing text with boolean type

2. Which of the following is the correct syntax to add a non-nullable string column named title with a default value 'Untitled' in a Rails migration?

easy

A. add_column :books, :title, :text, null: false, default: 'Untitled'

B. add_column :books, :title, :string, default: 'Untitled', null: true

C. add_column :books, :title, :string, null: false, default: 'Untitled'

D. add_column :books, :title, :string, null: false

Solution

1. Step 1: Identify correct column type and options

   We want a string type with null: false and default: 'Untitled'.

2. Step 2: Check syntax order and options

   add_column :books, :title, :string, null: false, default: 'Untitled' correctly uses :string, null: false, and default: 'Untitled'. The option with null: true allows null values. The option with :text uses the wrong type. The option without default misses the default value.

3. Final Answer:

   add_column :books, :title, :string, null: false, default: 'Untitled' -> Option C

4. Quick Check:

   Correct syntax with null and default options [OK]

Hint: Use null: false and default: 'value' together in add_column [OK]

Common Mistakes:

• Forgetting null: false for required columns
• Using wrong column type like text instead of string
• Omitting default value when needed

3. Given this migration snippet:

create_table :users do |t|
  t.integer :age, null: false, default: 18
  t.boolean :active, default: true
end

What will be the default value of active for a new user if not specified?

medium

A. true

B. false

C. nil

D. 0

Solution

1. Step 1: Read the default value for active

   The migration sets default: true for the boolean column active.

2. Step 2: Understand default behavior

   If no value is given when creating a user, active will be set to true automatically.

3. Final Answer:

   true -> Option A

4. Quick Check:

   Boolean default true means new records get true [OK]

Hint: Default value sets initial data if none provided [OK]

Common Mistakes:

• Assuming default is false if not specified
• Confusing nil with default value
• Thinking integer 0 is default for boolean

4. You wrote this migration line:

add_column :orders, :price, :integer, null: true, default: 0

But you want to ensure price is always set and never null. What is the fix?

medium

A. Add null: true, default: nil

B. Change null: true to null: false

C. Change :integer to :float

D. Remove default: 0

Solution

1. Step 1: Identify null constraint

   Currently null: true allows price to be null, which is not desired.

2. Step 2: Fix null constraint

   Changing null: true to null: false ensures price cannot be null.

3. Final Answer:

   Change null: true to null: false -> Option B

4. Quick Check:

   Use null: false to prevent null values [OK]

Hint: null: false means column must have a value [OK]

Common Mistakes:

• Leaving null: true when value must be required
• Removing default without fixing null
• Changing type without addressing null

5. You want to add a status column to your tasks table that stores short text but limits it to 10 characters, defaults to 'pending', and cannot be null. Which migration line is correct?

hard

A. add_column :tasks, :status, :string, limit: 255, null: false, default: 'pending'

B. add_column :tasks, :status, :text, null: false, default: 'pending'

C. add_column :tasks, :status, :string, null: true, default: 'pending'

D. add_column :tasks, :status, :string, limit: 10, null: false, default: 'pending'

Solution

1. Step 1: Choose correct column type and limit

   Use :string with limit: 10 to restrict text length to 10 characters.

2. Step 2: Set null and default options

   Set null: false to require a value and default: 'pending' for initial value.

3. Final Answer:

   add_column :tasks, :status, :string, limit: 10, null: false, default: 'pending' -> Option D

4. Quick Check:

   String with limit, null false, and default set [OK]

Hint: Use limit to restrict string length in migrations [OK]

Common Mistakes:

• Using text type which ignores limit
• Allowing null when value is required
• Setting wrong limit size