Conditional validations in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to validate presence of :email only if :newsletter is true.

Ruby on Rails

validates :email, presence: true, if: [1]

Drag options to blanks, or click blank then click option'

A:newsletter == true

Bnewsletter == true

C-> { newsletter }

D:newsletter

Attempts:

3 left

💡 Hint

Common Mistakes

Using a symbol instead of a lambda for the :if option.

Writing a comparison directly without a lambda.

The if option accepts a lambda to conditionally run the validation. Here, -> { newsletter } checks if newsletter is true.

2fill in blank

medium

Complete the code to validate :age numericality only if :adult is true.

Ruby on Rails

validates :age, numericality: true, if: [1]

Drag options to blanks, or click blank then click option'

A:adult

B-> { adult }

Cadult == true

D-> adult

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a symbol instead of a lambda.

Using invalid lambda syntax.

The if option needs a lambda that returns true when adult is true. -> { adult } works correctly.

3fill in blank

hard

Fix the error in the validation to run only if :active is true.

Ruby on Rails

validates :username, presence: true, if: [1]

Drag options to blanks, or click blank then click option'

Aactive?

Bactive == true

C:active

D-> { active? }

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a symbol without method name.

Using a boolean expression directly without a lambda.

The if option expects a lambda or symbol. Using -> { active? } correctly calls the method to check if the record is active.

4fill in blank

hard

Fill in the blank to validate :phone presence only if :contact_method equals 'phone'.

Ruby on Rails

validates :phone, presence: true, if: [1]

Drag options to blanks, or click blank then click option'

A-> { contact_method == 'phone' }

B:contact_method

C-> { contact_method === 'phone' }

Dcontact_method == 'phone'

Attempts:

3 left

💡 Hint

Common Mistakes

Using triple equals (===) which is not typical for string comparison.

Passing a symbol instead of a lambda.

The if option needs a lambda that returns true when contact_method equals 'phone'. The lambda -> { contact_method == 'phone' } works correctly.

5fill in blank

hard

Fill in the blank to validate :password presence only if :user_signed_in is false and :guest_user is true.

Ruby on Rails

validates :password, presence: true, if: [1]

Drag options to blanks, or click blank then click option'

A-> { !user_signed_in && guest_user }

B-> { user_signed_in == false && guest_user == true }

C-> { !user_signed_in and guest_user }

D-> { user_signed_in != true && guest_user }

Attempts:

3 left

💡 Hint

Common Mistakes

Using and instead of && which has different precedence.

Writing conditions outside a lambda.

The if option needs a lambda that returns true only when user_signed_in is false and guest_user is true. The lambda -> { !user_signed_in && guest_user } is clear and correct.

Practice

1. What does a conditional validation in Rails do?

easy

A. Runs validation only when a specific condition is true

B. Runs validation on every save regardless of conditions

C. Disables all validations temporarily

D. Automatically fixes invalid data

Solution

1. Step 1: Understand the purpose of conditional validations

   Conditional validations allow validations to run only if certain conditions are met, making them flexible.

2. Step 2: Compare options with this purpose

   Only Runs validation only when a specific condition is true describes running validation based on a condition, matching the concept.

3. Final Answer:

   Runs validation only when a specific condition is true -> Option A

4. Quick Check:

   Conditional validation = run if condition true [OK]

Hint: Conditional validations run only when conditions are true [OK]

Common Mistakes:

• Thinking validations always run on every save
• Confusing conditional validations with disabling validations
• Believing validations fix data automatically

2. Which of the following is the correct syntax to add a conditional validation using if with a method named active??

easy

A. validates :name, presence: true if :active?

B. validates :name, presence: true, if: :active?

C. validates :name, presence: true, if active?

D. validates :name, presence: true, if => :active?

Solution

1. Step 1: Recall correct syntax for conditional validations

   Rails uses a hash key if: followed by a symbol or lambda for conditions.

2. Step 2: Match options with correct syntax

   validates :name, presence: true, if: :active? correctly uses if: :active?. Others have syntax errors or missing commas.

3. Final Answer:

   validates :name, presence: true, if: :active? -> Option B

4. Quick Check:

   Use if: :method_name for conditional validation [OK]

Hint: Use if: :method_name with a comma for conditional validations [OK]

Common Mistakes:

• Omitting comma before if
• Using if without colon or symbol
• Using wrong hash rocket syntax

3. Given this model code:

class User < ApplicationRecord
  validates :email, presence: true, unless: :guest?
  def guest?
    role == 'guest'
  end
end

What happens when you save a User with role = 'guest' and email = nil?

medium

A. Validation fails because role is not checked

B. Validation fails because email is missing

C. Raises an error due to missing email

D. Validation passes because guest users skip email validation

Solution

1. Step 1: Understand the conditional validation with unless

   The validation runs unless the guest? method returns true. If user is guest, validation is skipped.

2. Step 2: Apply to given user data

   User has role 'guest', so guest? returns true, skipping email presence validation. So saving passes despite missing email.

3. Final Answer:

   Validation passes because guest users skip email validation -> Option D

4. Quick Check:

   unless: :guest? skips validation if guest? true [OK]

Hint: unless skips validation when condition method returns true [OK]

Common Mistakes:

• Assuming validation always runs regardless of unless
• Confusing unless with if
• Expecting error instead of skip

4. Identify the error in this validation code:

validates :age, numericality: true, if: user.adult?

medium

A. No error, code is correct

B. Missing comma after numericality: true

C. Using method call instead of symbol for if condition

D. numericality should be a method, not an option

Solution

1. Step 1: Check syntax for conditional validation if option

   The if: option expects a symbol or lambda, not a method call.

2. Step 2: Analyze given code

   Here, user.adult? is a method call, which is invalid syntax in validation options.

3. Final Answer:

   Using method call instead of symbol for if condition -> Option C

4. Quick Check:

   Use symbol (:method_name), not method call, for if condition [OK]

Hint: Use :method_name symbol, not method call, in if condition [OK]

Common Mistakes:

• Calling method instead of passing symbol
• Confusing method call with symbol
• Ignoring syntax errors in validation options

5. You want to validate presence of phone_number only if the user is an admin or if the account is active. Which is the correct way to write this conditional validation?

hard

A. validates :phone_number, presence: true, if: -> { admin? || active? }

B. validates :phone_number, presence: true, if: :admin? && :active?

C. validates :phone_number, presence: true, if: [:admin?, :active?]

D. validates :phone_number, presence: true, if: admin? or active?

Solution

1. Step 1: Understand combining conditions in validations

   To combine multiple conditions, use a lambda with logical operators inside the if: option.

2. Step 2: Evaluate each option's syntax

   validates :phone_number, presence: true, if: -> { admin? || active? } uses a lambda with admin? || active?, which is correct. Others misuse symbols or syntax.

3. Final Answer:

   validates :phone_number, presence: true, if: -> { admin? || active? } -> Option A

4. Quick Check:

   Use lambda with || to combine conditions in if [OK]

Hint: Use lambda with || to combine multiple conditions in if [OK]

Common Mistakes:

• Using && or || with symbols directly
• Passing array of symbols instead of lambda
• Writing invalid Ruby syntax in if option