Ruby on Rails quiz — 22 questions with answers and explanations

Answer: B

By naming and organizing folders by convention, Rails wires the pieces together without any declarations: a singular model class matches a plural table, the file name matches the class name, and the folder matches the role.

Answer: A

A migration describes schema changes as ordered steps, recorded as having run or not. That way every environment applies the same sequence of changes and the local schema matches the server.

Answer: D

It creates the seven standard routes for list, show, new form, create, edit form, update, and destroy. They map to the controller actions of the same name following the naming convention.

Answer: A

It prevents mass assignment to columns that aren't allowed: a user adds a field to the form and can then edit a column that flags admin rights. The controller must explicitly list which fields are accepted.

Answer: A

It records the exact version of every resolved library, including transitive dependencies. That way the local machine, CI, and the server install the same set, so it must be committed to the repo.

Answer: D

Through an environment variable that specifies which environment is running, and Rails loads the matching config file. That way the development build enables detailed error reporting and code reloading, while the production build enables caching and hides error details.

Answer: A

Eager-load the relationship when querying the list. Rails will run one query for the posts and one query that gathers all authors by list of keys, instead of one query per post.

Answer: A

The relation is executed when the result is actually used, for example when iterating or when counting. Thanks to lazy execution, chained filter conditions are combined into a single query instead of running step by step.

Answer: A

Because the check and the write are two separate steps: two concurrent requests both see that no record exists yet and then both write. To be sure, you must add a unique constraint at the database and catch the violation error.

Answer: C

They run implicitly on every record write, including from manual scripts or data import tasks. Sending email in a callback means a bulk import will unintentionally send thousands of emails.

Answer: D

On large tables, this can lock the table for a long time and cause downtime, depending on the database version. The safe approach is to add a nullable column first, backfill in batches, then add the constraint.

Answer: D

Jobs must be idempotent — rerunning them yields the same result, because queues guarantee at-least-once delivery. A non-idempotent charge job could deduct money twice when retried after a network failure.

Answer: D

The cache key is built from the record's identifier and updated timestamp. When the record changes the key changes and the old cache entry is automatically invalidated, so no manual cache expiration code is needed.

Answer: B

Rendering logic lives in a single place on the server, so you don't have to duplicate UI rendering in JavaScript. This lets small teams ship more features without maintaining two rendering layers.

Answer: B

Extract business flows into separate classes with clear responsibilities, e.g., one class for registration and one for cancellation. Mixing modules into the model only splits the file without reducing the object's responsibilities.

Answer: B

Fixtures are loaded once for the entire test suite so they are fast but shared and prone to hidden dependencies. Factories generate data per test so each test describes its own setup, but are slower.

Answer: A

It prevents another website from submitting requests on behalf of a logged-in user. Since the browser automatically sends the session, the server needs a token to prove the request originated from its own pages.

Answer: C

User input becomes part of the query and can completely change its meaning, allowing out-of-scope reads or data deletion. The correct fix is to use parameter binding so values are always treated as data.

Answer: A

Store on an external storage service and offload transformations like thumbnail generation to background jobs. Storing on the app server's disk loses files on redeploy and cannot be shared across multiple machines.

Answer: A

The business condition is explicitly named and composable: the code reads as intent rather than a chain of raw conditions, and combining several conditions still produces a single query.

Answer: B

The transaction stays open while waiting on the network, holding a connection and keeping locks longer than necessary. Worse, if the transaction rolls back, the external call has already happened and cannot be undone.

Answer: A

Use optimistic locking: the record has a version column, and a write based on a stale version is rejected instead of overwriting. The application catches that error and tells the user the record was modified by someone else.