has_one relationship in Ruby on Rails - Mini Project: Build & Apply

Understanding has_one Relationship in Rails

📖 Scenario: You are building a simple Rails app to manage users and their profiles. Each user has exactly one profile with personal details.

🎯 Goal: Create a User model and a Profile model with a has_one relationship from User to Profile. Set up the database tables and associations correctly.

📋 What You'll Learn

Create a User model with a has_one :profile association

Create a Profile model with a belongs_to :user association

Add a foreign key user_id to the profiles table

Use Rails conventions for migrations and model files

💡 Why This Matters

🌍 Real World

Many apps have users with one profile containing personal info. This pattern keeps data organized and easy to access.

💼 Career

Understanding has_one relationships is essential for Rails developers to model real-world data correctly and build maintainable apps.

1

Create the User model

Generate a Rails model called User with a string attribute name. Write the model file app/models/user.rb with the class User inheriting from ApplicationRecord.

Ruby on Rails

# Create the User model class in app/models/user.rb
# Your code here

Need a hint?

The User model file should define a class User that inherits from ApplicationRecord.

2

Create the Profile model with user_id foreign key

Generate a Rails model called Profile with string attributes bio and location. Add a foreign key user_id to the profiles table. Write the model file app/models/profile.rb with the class Profile inheriting from ApplicationRecord.

Ruby on Rails

class User < ApplicationRecord
end

# Create the Profile model class in app/models/profile.rb
# Your code here

Need a hint?

The Profile model file should define a class Profile that inherits from ApplicationRecord. The migration should add user_id as a foreign key.

3

Add associations between User and Profile models

In the User model, add has_one :profile. In the Profile model, add belongs_to :user.

Ruby on Rails

class User < ApplicationRecord
  # Add has_one association here
  # Your code here
end

class Profile < ApplicationRecord
  # Add belongs_to association here
  # Your code here
end

Need a hint?

Use has_one :profile in User and belongs_to :user in Profile.

4

Add migration to create profiles table with user_id

Write a migration to create the profiles table with string columns bio and location, and a user_id column as a foreign key referencing users. Use t.references :user, foreign_key: true in the migration.

Ruby on Rails

class User < ApplicationRecord
  has_one :profile
end

class Profile < ApplicationRecord
  belongs_to :user
end

# Write migration code here
# Your code here

Need a hint?

Use create_table :profiles and add t.references :user, foreign_key: true to link profiles to users.