Dependent destroy and nullify in Ruby on Rails - Mini Project: Build & Apply

Dependent destroy and nullify in Rails associations

📖 Scenario: You are building a simple blog application where each Author can have many Posts. When an author is deleted, you want to control what happens to their posts.

🎯 Goal: Learn how to use dependent: :destroy and dependent: :nullify in Rails models to manage associated records when the parent record is deleted.

📋 What You'll Learn

Create an Author model with a has_many :posts association

Create a Post model with a belongs_to :author association

Add dependent: :destroy to the Author model association

Add dependent: :nullify to the Author model association

Understand the difference in behavior when deleting an author

💡 Why This Matters

🌍 Real World

Managing data relationships in web apps is common. Knowing how to control what happens to related data when deleting records helps keep data clean and consistent.

💼 Career

Rails developers often work with associations and must understand dependent options to avoid data loss or orphaned records.

1

Create Author and Post models with associations

Create a Rails model called Author with a has_many :posts association and a Rails model called Post with a belongs_to :author association.

Ruby on Rails

# Create Author and Post models with associations

class Author < ApplicationRecord
  # Your code here
end

class Post < ApplicationRecord
  # Your code here
end

Need a hint?

Use has_many :posts inside the Author model and belongs_to :author inside the Post model.

2

Add dependent: :destroy to Author's posts association

Modify the Author model to add dependent: :destroy to the has_many :posts association to delete posts when an author is deleted.

Ruby on Rails

class Author < ApplicationRecord
  # Add dependent: :destroy to posts association
  has_many :posts, dependent: :destroy
end

class Post < ApplicationRecord
  belongs_to :author
end

Need a hint?

Add dependent: :destroy inside the has_many :posts association in the Author model.

3

Change dependent option to :nullify

Change the dependent option in the Author model's has_many :posts association from :destroy to :nullify so posts are not deleted but their author_id is set to NULL when an author is deleted.

Ruby on Rails

class Author < ApplicationRecord
  # Change dependent option to :nullify
  has_many :posts, dependent: :nullify
end

class Post < ApplicationRecord
  belongs_to :author
end

Need a hint?

Replace dependent: :destroy with dependent: :nullify in the has_many :posts association.

4

Add optional: true to Post's belongs_to association

Modify the Post model's belongs_to :author association to add optional: true so posts can exist without an author after nullification.

Ruby on Rails

class Author < ApplicationRecord
  has_many :posts, dependent: :nullify
end

class Post < ApplicationRecord
  # Add optional: true to belongs_to association
  belongs_to :author, optional: true
end

Need a hint?

Add optional: true inside the belongs_to :author association in the Post model.