Conditional validations in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when conditional validation is triggered?

Consider this Rails model snippet:

class User < ApplicationRecord
  validates :email, presence: true, if: :email_required?

  def email_required?
    age >= 18
  end
end

What is the validation behavior when a User is 17 years old and email is blank?

A Validation passes because email presence is only checked if age is 18 or more.

B Validation passes only if email is blank and age is exactly 17.

C Validation fails because age is less than 18 but email is blank.

D Validation fails because email must always be present.

💡 Hint

Look at the condition method email_required? and when it returns true.

The validation for email presence runs only if email_required? returns true. Since age is 17, email_required? returns false, so email presence is not validated.

📝 Syntax

intermediate

Identify the correct syntax for conditional validation using :unless

Which option correctly uses :unless to skip validation when the user is an admin?

class User < ApplicationRecord
  # Validate presence of password unless user is admin
end

A validates :password, presence: true, unless: admin?

B validates :password, presence: true, unless: :admin?

C validates :password, presence: true, unless: admin

D validates :password, presence: true, unless: -> { admin? }

💡 Hint

The :unless option expects a symbol referencing a method name.

The :unless option takes a symbol for a method name that returns true or false. Option B correctly uses :admin? as a symbol.

🔧 Debug

advanced

Why does this conditional validation never run?

Given this model:

class Product < ApplicationRecord
  validates :price, numericality: true, if: :on_sale

  def on_sale
    sale == true
  end
end

Why might the price validation never trigger even when sale is true?

A The method on_sale should be named on_sale? with a question mark.

B The if option expects a symbol, but :on_sale is a method returning a boolean, so it works fine.

C The validation needs to use unless instead of if to work correctly.

D The sale attribute might be a string 'true' instead of boolean true, causing on_sale to return false.

💡 Hint

Check the data type of the sale attribute and how Ruby compares true with 'true'.

If sale is stored as a string 'true', the comparison sale == true returns false, so on_sale returns false and validation does not run.

❓ state_output

advanced

What is the validation error output for this conditional validation?

Consider this model:

class Order < ApplicationRecord
  validates :shipping_address, presence: true, if: -> { delivery_required }

  def delivery_required
    delivery == 'yes'
  end
end

order = Order.new(delivery: 'yes', shipping_address: '')
order.valid?
order.errors.full_messages

What is the output of order.errors.full_messages?

A [] (empty array)

B ["Delivery must be yes"]

C ["Shipping address can't be blank"]

D ["Shipping address is invalid"]

💡 Hint

The validation runs only if delivery_required returns true.

Since delivery is 'yes', delivery_required returns true, so shipping_address presence is validated. It is blank, so error is added.

🧠 Conceptual

expert

Which conditional validation approach is best for complex logic?

You want to validate an attribute only if multiple conditions are met, including checking user role, time of day, and a feature flag. Which approach is best in Rails?

A Use a single method that returns true or false combining all conditions, then use if: :method_name.

B Chain multiple validations each with simple if conditions for each check separately.

C Use a lambda with all conditions inside for the if option.

D Use validates with unless option negating all conditions.

💡 Hint

Think about maintainability and clarity for complex conditions.

A single method encapsulating all logic keeps validation clean and easy to maintain. Lambdas can be used but may become hard to read if complex.