# ActiveStorage (Ruby on Rails)

> File uploads, attachments, has_one_attached, has_many_attached, S3, variants, previews

- 20 interview questions
- Mid-Level
- [Interview Questions: Ruby on Rails](https://sharpskill.dev/en/technologies/ruby-on-rails/interview-questions.md)

## 1. Which command should be used to install ActiveStorage in a Rails application?

**Answer**

The rails active_storage:install command generates the necessary migrations to create the active_storage_blobs and active_storage_attachments tables. These tables store metadata about uploaded files. After installation, run rails db:migrate to apply the migrations to the database.

## 2. Which macro should be used to attach a single file (avatar) to a User model?

**Answer**

The has_one_attached macro allows attaching a single file to a model. It automatically creates the methods avatar, avatar=, avatar.attach, avatar.attached? and avatar.purge. For multiple files, use has_many_attached instead.

## 3. Which macro should be used to attach multiple files (documents) to a Project model?

**Answer**

The has_many_attached macro allows attaching multiple files to a model. It creates the methods documents, documents.attach, documents.attached? and documents.purge. Files are stored in a collection and can be added or removed individually.

## 17 more questions available

- Which method should be used to check if a file is already attached to a record?
- In which configuration file should the default storage service (local, S3, etc.) be defined?

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