Numericality validation in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a model with numericality validation receives a non-numeric value?

Consider a Rails model with validates :age, numericality: true. What will be the validation result if age is set to 'twenty'?

Ruby on Rails

class User < ApplicationRecord
  validates :age, numericality: true
end

user = User.new(age: 'twenty')
user.valid?
user.errors.full_messages

A Validation raises a runtime error because 'twenty' cannot be converted to a number.

B Validation passes because 'twenty' is a string and strings are allowed.

C Validation fails with an error message saying age is not a number.

D Validation ignores the age attribute and passes.

💡 Hint

Think about what numericality validation expects as input.

The numericality validation checks if the attribute is a valid number. A string like 'twenty' is not numeric, so validation fails with an error message.

📝 Syntax

intermediate

Which validation syntax correctly enforces an integer value only?

You want to validate that the attribute quantity is an integer number only. Which of the following validation lines is correct?

A validates :quantity, numericality: { only_integer: true }

B validates :quantity, numericality: true, only_integer: true

C validates :quantity, only_integer: true

D validates :quantity, numericality: { integer_only: true }

💡 Hint

Check the correct option key inside the numericality hash.

The correct option is only_integer: true inside the numericality hash. Other options are either misplaced or incorrect keys.

❓ state_output

advanced

What is the error message when a number is less than the minimum allowed?

Given the validation validates :score, numericality: { greater_than_or_equal_to: 10 }, what error message appears if score is set to 5?

Ruby on Rails

class Game < ApplicationRecord
  validates :score, numericality: { greater_than_or_equal_to: 10 }
end

game = Game.new(score: 5)
game.valid?
game.errors.full_messages

A ["Score must be greater than 10"]

B ["Score must be at least 5"]

C ["Score is not a number"]

D ["Score must be greater than or equal to 10"]

💡 Hint

Look carefully at the validation option used.

The validation uses greater_than_or_equal_to: 10, so the error message reflects that the score must be at least 10.

🔧 Debug

advanced

Why does this numericality validation not work as expected?

This model validation is intended to allow only positive integers, but it accepts negative numbers. Why? validates :count, numericality: { only_integer: true, greater_than: 0 }

Ruby on Rails

class Item < ApplicationRecord
  validates :count, numericality: { only_integer: true, greater_than: 0 }
end

item = Item.new(count: -3)
item.valid?
item.errors.full_messages

A The validation fails because the attribute is a string, not an integer.

B The validation works correctly; negative numbers are rejected with an error.

C The validation is missing the presence check, so nil values pass.

D The validation allows negative numbers because only_integer does not check sign.

💡 Hint

Try running the code and check the errors.

The validation correctly rejects negative numbers because of greater_than: 0. Negative values cause validation to fail.

🧠 Conceptual

expert

How does the allow_nil option affect numericality validation?

Consider validates :price, numericality: true, allow_nil: true. What is the behavior when price is nil?

A Validation passes and no error is added because nil is allowed.

B Validation fails because nil is not a number.

C Validation ignores the attribute completely, even if it has a value.

D Validation raises an exception due to nil value.

💡 Hint

Think about what allow_nil means for validations.

The allow_nil: true option skips numericality validation if the attribute is nil, so validation passes without errors.