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

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a model with presence validation is saved with a blank attribute?

Consider a Rails model with validates :name, presence: true. What will be the result of model.save if name is blank?

Ruby on Rails

class User < ApplicationRecord
  validates :name, presence: true
end

user = User.new(name: "")
saved = user.save

A The save returns false and the user is not saved to the database.

B The save returns true and the user is saved with an empty name.

C The save raises a runtime error because name is blank.

D The save returns nil and the user is partially saved.

💡 Hint

Think about what presence validation checks before saving.

Presence validation prevents saving if the attribute is blank. So, save returns false and the record is not saved.

📝 Syntax

intermediate

Which option correctly adds presence validation for multiple attributes?

You want to validate presence of both email and username in a Rails model. Which code is correct?

Ruby on Rails

class Account < ApplicationRecord
  # Add presence validation here
end

A validates :email, :username, presence: true

B validates [:email, :username], presence: true

C validates :email, presence: true, :username, presence: true

D validates presence: true, attributes: [:email, :username]

💡 Hint

Check the syntax for multiple attributes in validates.

The correct syntax is to list attributes separated by commas before the validation option.

🔧 Debug

advanced

Why does this presence validation not work as expected?

Given this model code, why does saving a user with blank name still succeed?

class User < ApplicationRecord
  validates :name, presence: true, allow_blank: true
end

user = User.new(name: "")
saved = user.save

A The name attribute is not a string, so validation is skipped.

B The presence validation requires allow_blank: false to work, which is missing here.

C The save method is overridden and ignores validations.

D The option allow_blank: true disables the presence validation, so blank names are allowed.

💡 Hint

Check what allow_blank: true does in presence validation.

allow_blank: true tells Rails to skip presence validation if the attribute is blank, so blank names are allowed.

❓ state_output

advanced

What is the content of errors after failed presence validation?

After trying to save a model with blank title and presence validation, what will model.errors[:title] contain?

Ruby on Rails

class Post < ApplicationRecord
  validates :title, presence: true
end

post = Post.new(title: "")
post.save
errors = post.errors[:title]

A ["is invalid"]

B [] (empty array)

C ["can't be blank"]

D nil

💡 Hint

What message does presence validation add on failure?

Presence validation adds the error message "can't be blank" to the attribute's errors array.

🧠 Conceptual

expert

How does presence validation treat whitespace-only strings?

In Rails, if a model has validates :description, presence: true, what happens when description is a string with only spaces, like " "?

A The validation raises an error due to invalid input type.

B The validation fails because whitespace-only strings are treated as blank.

C The validation passes because the string is not empty.

D The validation ignores whitespace and saves the record.

💡 Hint

Think about how Rails treats strings with only spaces in presence validation.

Rails treats strings with only whitespace as blank, so presence validation fails for such strings.