Ruby on Rails Case Studies & Practical Application 3

Question 1

A Rails app's homepage makes 12 database queries on every load. After profiling, navigation categories are queried every request. Best fix?

Accepted Answer

Cache the navigation fragment with Rails.cache or fragment caching

Answer

Fragment or low-level caching stores the rendered or queried result, eliminating repeated DB hits for static-ish data.

Question 2

You are deploying a Rails app and must run database migrations without downtime. Which strategy is safest for a high-traffic production app?

Accepted Answer

Use additive migrations and deploy code before removing old columns in a follow-up migration

Answer

Additive migrations paired with a two-phase deploy avoid locking tables during traffic.

Question 3

Your Rails API returns sensitive user data in JSON responses because serializers are not filtering attributes. Which approach best solves this?

Accepted Answer

Use a serializer library to explicitly whitelist attributes returned per resource

Answer

Serializer libraries enforce an explicit allowlist of returned attributes, making accidental data exposure much harder.

Question 4

A legacy Rails 4 app uses attr_accessible for mass-assignment protection. In Rails 5+, this is removed. What replaces it?

Accepted Answer

Strong Parameters via require and permit in the controller

Answer

Strong Parameters (params.require(:model).permit(:field)) moved mass-assignment protection to the controller layer starting in Rails 4+.

Question 5

A Rails app processes large CSV imports synchronously, causing 30-second HTTP timeouts. What is the correct pattern?

Accepted Answer

Accept the upload, enqueue a background job to process it, and return a job ID immediately

Answer

Returning a job ID immediately and processing asynchronously prevents HTTP timeouts and gives users a way to check progress.

Ruby on Rails Practice Test