Ruby on Rails Ruby on Rails ActiveRecord & Database Management 2

Question 1

What does `validates :title, presence: true` do in an ActiveRecord model?

Accepted Answer

Ensures the title field is not blank before saving

Answer

`validates :title, presence: true` adds a model-level validation that prevents saving if the title attribute is blank or nil.

Question 2

What is a Rails migration's `change` method used for?

Accepted Answer

Defining reversible database schema changes

Answer

The `change` method defines reversible schema migrations; Rails knows how to automatically reverse operations like `add_column` and `create_table`.

Question 3

Which ActiveRecord query method returns only the first matching record or nil?

Accepted Answer

Model.find_by

Answer

`Model.find_by(conditions)` returns the first record matching the given conditions, or nil if none is found.

Question 4

What does `db/schema.rb` represent in a Rails application?

Accepted Answer

A snapshot of the current database schema after all migrations

Answer

schema.rb is auto-generated by Rails to reflect the current cumulative state of all applied migrations.

Question 5

In ActiveRecord, what does `scope :published, -> { where(published: true) }` define?

Accepted Answer

A class method that applies a reusable named query filter

Answer

A `scope` defines a reusable, chainable query that can be called like `Article.published` to filter records.

Ruby on Rails Practice Test