Presence validation in Ruby on Rails - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is presence validation in Rails?

Presence validation ensures that a specific attribute is not empty or nil before saving a record in the database.

beginner

How do you add presence validation to a model attribute in Rails?

Use validates :attribute_name, presence: true inside the model class.

beginner

What happens if a presence validation fails when saving a record?

The record is not saved, and error messages are added to the model's errors collection.

intermediate

Can presence validation check multiple attributes at once?

Yes, you can validate multiple attributes by listing them: validates :name, :email, presence: true.

beginner

Why is presence validation important in web applications?

It prevents saving incomplete or invalid data, ensuring the app works correctly and data stays reliable.

Which Rails method is used to enforce presence validation on a model attribute?

A validates :attribute, presence: true

B validate_presence_of :attribute

C check_presence :attribute

D require :attribute

The correct syntax is validates :attribute, presence: true to enforce presence validation.

What will happen if a model fails presence validation when calling save?

A The record will save anyway

B The attribute will be auto-filled

C The app will crash

D The record will not save and errors will be added

If presence validation fails, the record is not saved and error messages are added to the model.

Can you validate presence for multiple attributes in one line?

A Yes, but only for string attributes

B No, you must validate each attribute separately

C Yes, by listing attributes like <code>validates :name, :email, presence: true</code>

D No, Rails does not support multiple attributes in presence validation

Rails allows validating presence for multiple attributes by listing them in one validates call.

Which of these values will fail presence validation?

A "Hello"

B " " (a space)

C nil

D 0

Presence validation fails if the attribute is nil or blank (including whitespace-only strings like " "). "Hello" and 0 are present.

Where do you place presence validation code in a Rails app?

A In the model

B In the database schema

C In the view

D In the controller

Presence validation is declared inside the model class to check data before saving.

Explain how to add presence validation to a Rails model and what it does.

Think about where validations go and what presence means.

Why is presence validation useful in a web application? Give an example.

Consider what happens if important info is missing.