Conditional validations in Ruby on Rails - Mini Project: Build & Apply

Conditional Validations in Rails Model

📖 Scenario: You are building a simple Rails application to manage user profiles. Some users are students, and some are teachers. You want to make sure that if a user is a student, they must provide their school_name. If the user is a teacher, they must provide their subject. This helps keep your data clean and relevant.

🎯 Goal: Create a Rails model User with conditional validations that require school_name only if the user is a student, and require subject only if the user is a teacher.

📋 What You'll Learn

Create a User model with attributes role, school_name, and subject.

Add a validation that requires school_name only when role is "student".

Add a validation that requires subject only when role is "teacher".

Use Rails built-in validation methods with conditional options.

💡 Why This Matters

🌍 Real World

Conditional validations are common in real apps where certain fields are required only in specific situations, like user roles or product types.

💼 Career

Understanding conditional validations helps you write flexible and robust Rails models, a key skill for backend web development jobs.

1

Create the User model with attributes

Create a Rails model class called User with attributes role, school_name, and subject defined as attr_accessors.

Ruby on Rails

class User
  # Define attributes role, school_name, subject
  # Your code here
end

Need a hint?

Use attr_accessor to create getter and setter methods for the attributes.

2

Add role constants for clarity

Inside the User class, add two constants: STUDENT_ROLE set to "student" and TEACHER_ROLE set to "teacher".

Ruby on Rails

class User
  attr_accessor :role, :school_name, :subject

  # Define STUDENT_ROLE and TEACHER_ROLE constants
  # Your code here
end

Need a hint?

Constants are written in uppercase letters and help avoid magic strings.

3

Add conditional validations for school_name and subject

Add validations inside the User class: validate presence of school_name only if role equals STUDENT_ROLE, and validate presence of subject only if role equals TEACHER_ROLE. Use the if: option with lambda functions.

Ruby on Rails

class User
  attr_accessor :role, :school_name, :subject

  STUDENT_ROLE = "student"
  TEACHER_ROLE = "teacher"

  # Add conditional validations for school_name and subject
  # Your code here
end

Need a hint?

Use validates :attribute, presence: true, if: -> { condition } to add conditional validations.

4

Add initialize method to set attributes

Add an initialize method to the User class that accepts a hash with keys :role, :school_name, and :subject and sets the corresponding instance variables.

Ruby on Rails

class User
  attr_accessor :role, :school_name, :subject

  STUDENT_ROLE = "student"
  TEACHER_ROLE = "teacher"

  validates :school_name, presence: true, if: -> { role == STUDENT_ROLE }
  validates :subject, presence: true, if: -> { role == TEACHER_ROLE }

  # Add initialize method to set attributes from a hash
  # Your code here
end

Need a hint?

The initialize method sets instance variables from the given hash keys.