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

Challenge - 5 Problems

❓ component_behavior

intermediate

How does this length validation behave?

Consider this Rails model validation:

validates :username, length: { minimum: 3, maximum: 8 }

What happens if you try to save a user with username 'Jo'?

A The save fails because 'Jo' is longer than the maximum length 8.

B The save succeeds because 'Jo' is a valid string.

C The save succeeds but triggers a warning.

D The save fails because 'Jo' is shorter than the minimum length 3.

💡 Hint

Think about what minimum length means for a string.

The validation requires the username to be at least 3 characters. 'Jo' has only 2 characters, so the save fails.

📝 Syntax

intermediate

Which length validation syntax is correct?

Which of these is the correct way to validate that a Rails model's attribute 'title' has a length exactly 5 characters?

A validates :title, length: { min: 5, max: 5 }

B validates_length_of :title, equal_to: 5

C validates :title, length: { is: 5 }

D validates :title, length: 5

💡 Hint

Look for the official Rails length validation option for exact length.

The correct syntax uses the :is key inside the length hash to specify exact length.

❓ state_output

advanced

What error message appears for this validation?

Given this validation:

validates :password, length: { minimum: 6, too_short: 'must have at least %{count} characters' }

What error message will appear if password is '123'?

A "Password is invalid"

B "must have at least 6 characters"

C "Password is too short (minimum is 6 characters)"

D "Password must be at least 3 characters"

💡 Hint

The custom message uses %{count} to show the minimum length.

The error message uses the custom :too_short message and replaces %{count} with 6.

🔧 Debug

advanced

Why does this length validation not work as expected?

Look at this validation:

validates :code, length: { minimum: 4, maximum: 10, message: 'length must be between 4 and 10' }

Why might the error message not show when the code is too short or too long?

A The :message option applies to all length errors, but Rails expects separate messages for minimum and maximum.

B The :message option is ignored because it must be outside the length hash.

C The validation syntax is invalid and causes a syntax error.

D The attribute :code is missing from the model.

💡 Hint

Check how Rails handles error messages for length validations.

Rails expects separate messages like :too_short and :too_long inside the length hash. A single :message is ignored for length.

🧠 Conceptual

expert

How does length validation interact with nil values?

Given this validation:

validates :nickname, length: { maximum: 10 }

If the nickname is nil, what happens when saving the model?

A The validation passes because length validation ignores nil values by default.

B The validation fails because nil has no length.

C The validation raises a runtime error.

D The validation passes only if :allow_nil is set to true.

💡 Hint

Think about how Rails treats nil values in length validations by default.

Length validation skips nil values unless :allow_nil is false. So nil passes validation.