Custom validation methods in Ruby on Rails - Mini Project: Build & Apply

Custom Validation Methods in Rails

📖 Scenario: You are building a simple Rails application to manage user profiles. Each user must have a username that is unique and does not contain any spaces. You will create a custom validation method to check that the username has no spaces.

🎯 Goal: Build a Rails model with a custom validation method that ensures the username attribute contains no spaces.

📋 What You'll Learn

Create a User model with a username attribute

Add a custom validation method called username_cannot_contain_spaces

Use validate :username_cannot_contain_spaces to call the custom validation

Add an error message to username if it contains spaces

💡 Why This Matters

🌍 Real World

Custom validations help enforce business rules that built-in validations cannot cover, such as complex formats or cross-field checks.

💼 Career

Rails developers often write custom validations to ensure data integrity and provide clear feedback to users in web applications.

1

Create the User model with username attribute

Create a Rails model class called User that inherits from ApplicationRecord. Add an attribute accessor for username.

Ruby on Rails

class User < ApplicationRecord
  # Your code here
end

Need a hint?

Use attr_accessor :username inside the User class.

2

Add custom validation method declaration

Inside the User model, add a line to call the custom validation method named username_cannot_contain_spaces using validate :username_cannot_contain_spaces.

Ruby on Rails

class User < ApplicationRecord
  attr_accessor :username

  # Add custom validation call here
  # Your code here
end

Need a hint?

Use validate :username_cannot_contain_spaces to register the custom validation.

3

Define the custom validation method

Define a method called username_cannot_contain_spaces inside the User model. Inside this method, check if username includes a space character. If it does, add an error to username with the message "cannot contain spaces" using errors.add(:username, "cannot contain spaces").

Ruby on Rails

class User < ApplicationRecord
  attr_accessor :username

  validate :username_cannot_contain_spaces

  # Define the custom validation method here
  # Your code here
end

Need a hint?

Use safe navigation &. to avoid errors if username is nil.

4

Complete the User model with custom validation

Ensure the User model includes attr_accessor :username, the line validate :username_cannot_contain_spaces, and the full method username_cannot_contain_spaces as defined previously.

Ruby on Rails

class User < ApplicationRecord
  attr_accessor :username

  validate :username_cannot_contain_spaces

  def username_cannot_contain_spaces
    if username&.include?(' ')
      errors.add(:username, "cannot contain spaces")
    end
  end
end

# Model complete

Need a hint?

Review the full model to confirm all parts are included.