Author: Abhilash

Meanwhile we are setting up some UI for our app using Tailwind CSS, I have uploaded 2 images to our product in the rich text editor. Let’s discuss about this in this post.

Understanding Active Storage in Rails 8: A Deep Dive into Image Uploads

In our Rails 8 application, we recently tested uploading two images to a product using the rich text editor. This process internally triggers several actions within Active Storage. Let’s break down what happens behind the scenes.

How Active Storage Handles Image Uploads

When an image is uploaded, Rails 8 processes it through Active Storage, creating a new blob entry and storing it in the disk service. The following request is fired:

Processing by ActiveStorage::DirectUploadsController#create as JSON

Parameters: {"blob" => {"filename" => "floral-kurtha.jpg", "content_type" => "image/jpeg", "byte_size" => 107508, "checksum" => "GgNgNxxxxxxxjdPOLw=="}}

This request initiates a database entry in active_storage_blobs:

INSERT INTO "active_storage_blobs" ("key", "filename", "content_type", "service_name", "byte_size", "checksum", "created_at")
VALUES ('huk9dxxxxxxxx09e2cyiq', 'floral-kurtha.jpg', 'image/jpeg', 'local', 107312, 'Fxxxxxxd+bpRibo2EfvA==', '2025-03-31 08:10:07.232453')

Storing Files and Generating URLs

Once the blob entry is created, Rails stores the file on disk and generates a URL:

http://localhost:3000/rails/active_storage/disk/eyJfcmFpbHMiOnsiYSI6eyJxxxxxxx

This process triggers the ActiveStorage::DiskController, handling file storage via a PUT request:

Started PUT "/rails/active_storage/disk/eyJfcmFpbHMiOxxxxx"
Disk Storage (0.9ms) Uploaded file to key: hut9d0zxssxxxxxx
Completed 204 No Content in 96ms

Retrieving Images from Active Storage

After successfully storing the file, the application fetches the image via a GET request:

Started GET "/rails/active_storage/blobs/redirect/eyJfcmFpbHMiOxxxxxxxxxxfQ==--f9c556012577xxxxxxxxxxxxfa21/floral-kurtha-2.jpg"

This request is handled by:

Processing by ActiveStorage::Blobs::RedirectController#show as JPEG

The file is then served via the ActiveStorage::DiskController#show:

Redirected to http://localhost:3000/rails/active_storage/disk/eyJfcmFpbHMiOnsiZGxxxxxxxxxd048aae4ab5c30/floral-kurtha-2.jpg

Updating Records with Active Storage Attachments

When updating a product, the system also updates its associated images. The following Active Storage updates occur:

UPDATE "action_text_rich_texts" SET "body" = .... WHERE "action_text_rich_texts"."id" = 1

UPDATE "active_storage_blobs" SET "metadata" = '{"identified":true}' WHERE "active_storage_blobs"."id" = 3

INSERT INTO "active_storage_attachments" ("name", "record_type", "record_id", "blob_id", "created_at") VALUES ('embeds', 'ActionText::RichText', 1, 3, '2025-03-31 11:46:13.464597')

Additionally, Rails updates the updated_at timestamp of the associated records:

UPDATE "products" SET "updated_at" = '2025-03-31 11:46:13.523640' WHERE "products"."id" = 1

Best Practices for Active Storage in Rails 8

1. Use Direct Uploads: This improves performance by uploading files directly to cloud storage (e.g., AWS S3, Google Cloud Storage) instead of routing them through your Rails server.
2. Attach Images Efficiently: Use has_one_attached or has_many_attached for file associations in models.
3. Avoid Serving Files via Rails: Use a CDN or proxy service to serve images instead of relying on Rails controllers.
4. Clean Up Unused Blobs: Regularly remove orphaned blob records using ActiveStorage::Blob.unattached.destroy_all.
5. Optimize Image Processing: Use variants (image.variant(resize: "300x300").processed) to generate resized images efficiently.

In Rails 8, Active Storage uses two main tables for handling file uploads:

1. active_storage_blobs Table

This table stores metadata about the uploaded files but not the actual files. Each row represents a unique file (or “blob”) uploaded to Active Storage.

Columns in active_storage_blobs Table:

• id – Unique identifier for the blob.
• key – A unique key used to retrieve the file.
• filename – The original name of the uploaded file.
• content_type – The MIME type (e.g., image/jpeg, application/pdf).
• metadata – JSON data storing additional information (e.g., width/height for images).
• service_name – The storage service (e.g., local, amazon, google).
• byte_size – File size in bytes.
• checksum – A checksum to verify file integrity.
• created_at – Timestamp when the file was uploaded.

Example Entry in active_storage_blobs:

INSERT INTO "active_storage_blobs" 
("key", "filename", "content_type", "service_name", "byte_size", "checksum", "created_at") 
VALUES ('avevnp6eg1xxxxxxsz8it6267eou7', 'floral-kurtha-2.jpg', 'image/jpeg', 'local', 204800, '0U0cXxxxxxxxxx/1u47Szg==', '2025-03-31 11:45:07.232453');

👉 Purpose: This table acts as a record of stored files and their metadata.

2. active_storage_attachments Table

This table links blobs (files) to Active Record models. Instead of storing files directly in the database, Rails stores a reference to the blob.

Columns in active_storage_attachments Table:

• id – Unique identifier for the attachment.
• name – Name of the attachment (:avatar, :images, etc.).
• record_type – The model type associated with the file (User, Post, etc.).
• record_id – The ID of the record in the model (users.id, posts.id).
• blob_id – The corresponding ID from active_storage_blobs.
• created_at – Timestamp when the association was created.

Example Entry in active_storage_attachments:

INSERT INTO "active_storage_attachments" 
("name", "record_type", "record_id", "blob_id", "created_at") 
VALUES ('avatar', 'User', 1, 42, '2025-03-31 08:15:20.123456');

INSERT INTO "active_storage_attachments" 
("name", "record_type", "record_id", "blob_id", "created_at") 
VALUES ('embeds', 'ActionText::RichText', 1, 4, '2025-03-31 11:46:20.123456');

👉 Purpose: This table allows a single file to be attached to multiple records without duplicating the file itself.

Why Does Rails Need Both Tables?

1. Separation of Concerns:
   • active_storage_blobs tracks the files themselves.
   • active_storage_attachments links them to models.
2. Efficient File Management:
   • The same file can be used in multiple places without storing it multiple times.
   • If a file is no longer attached to any record, Rails can remove it safely.
3. Supports Different Attachments:
   • A model can have different types of attachments (avatar, cover_photo, documents).
   • A single model can have multiple files attached (has_many_attached).

Example Usage in Rails 8

class User < ApplicationRecord
  has_one_attached :avatar   # Single file
  has_many_attached :photos  # Multiple files
end

When a file is uploaded, an entry is added to active_storage_blobs, and an association is created in active_storage_attachments.

How Rails Queries These Tables

user.avatar # Fetches from `active_storage_blobs` via `active_storage_attachments`
user.photos.each { |photo| puts photo.filename } # Fetches multiple attached files

Conclusion

Rails 8 uses two tables to decouple file storage from model associations, enabling better efficiency, flexibility, and reusability. This structure allows models to reference files without duplicating them, making Active Storage a powerful solution for file management in Rails applications. 🚀

Where Are Files Stored in Rails 8 by Default?

By default, Rails 8 stores uploaded files using Active Storage’s disk service, meaning files are saved in the storage/ directory within your Rails project.

Default Storage Location:

• Files are stored in:
  storage/
├── cache/ (temporary files)
├── store/ (permanent storage)
└── variant/ (image transformations like resizing)
• The exact file path inside storage/ is determined by the key column in the active_storage_blobs table. For example, if a blob entry has: key = 'xyz123abcd' then the file is stored at: storage/store/xyz123abcd

How to Change the Storage Location?

You can configure storage in config/storage.yml. For example:

local:
  service: Disk
  root: <%= Rails.root.join("storage") %>

# Use bin/rails credentials:edit to set the AWS secrets (as aws:access_key_id|secret_access_key)
amazon:
  service: S3
  access_key_id: <%= Rails.application.credentials.dig(:aws, :access_key_id) %>
  secret_access_key: <%= Rails.application.credentials.dig(:aws, :secret_access_key) %>
  region: us-east-1
  bucket: your_own_bucket-<%= Rails.env %>

Then, update config/environments/development.rb (or production.rb) to use:

config.active_storage.service = :local  # or :amazon for S3

How to Get the Stored File Path in Rails 8 Active Storage

Since Rails stores files in a structured directory inside storage/, the actual file path can be determined using the key stored in the active_storage_blobs table.

Get the File Path in Local Storage

If you’re using the Disk service (default for development and test), you can retrieve the stored file path manually:

blob = ActiveStorage::Blob.last
file_path = Rails.root.join("storage", "store", blob.key)
puts file_path

🔹 Example Output:

/your_project/storage/store/xyz123abcd

💡 This path is internal and cannot be accessed directly from a browser.

How to Get the File URL

Instead of accessing the internal path, Active Storage provides methods to generate URLs for public access.

1. Generate a URL for Direct Access

If you want a publicly accessible URL, you can use:

Rails.application.routes.url_helpers.rails_blob_url(blob, host: "http://localhost:3000")

🔹 Example Output:

http://localhost:3000/rails/active_storage/blobs/redirect/eyJfcmFpbHMiO...--filename.jpg

This redirects to the actual file storage location.

2. Get a Temporary Signed URL

For direct storage services like S3 or Google Cloud Storage, you can generate a signed URL:

blob.service_url

🔹 Example Output (for S3 storage):

https://your-s3-bucket.s3.amazonaws.com/xyz123abcd?X-Amz-Signature=...

🔹 Example Output (for local storage, using Disk service):

http://localhost:3000/rails/active_storage/disk/eyJfcmFpbHMiO...

This signed URL expires after a set time (default is a few minutes).

3. Get a Variant URL for an Image

If your file is an image and you want a resized version, use:

variant = blob.variant(resize: "300x300").processed
Rails.application.routes.url_helpers.rails_representation_url(variant, host: "http://localhost:3000")

🔹 Example Output:

http://localhost:3000/rails/active_storage/representations/abcdxyz.../resize_300x300.jpg

Summary

• Files are stored in the storage/ directory by default.
• Use rails_blob_url or service_url to get an accessible URL.
• Use variant to generate resized versions.
• For production, it’s best to use a cloud storage service like Amazon S3.

Understanding has_one_attached and has_many_attached in Rails 8

Rails 8 provides a built-in way to handle file attachments through Active Storage. The key methods for attaching files to models are:

1. has_one_attached – For a single file attachment.
2. has_many_attached – For multiple file attachments.

Let’s break down what they do and why they are useful.

1. has_one_attached

This is used when a model should have a single file attachment. For example, a User model may have only one profile picture.

Usage:

class User < ApplicationRecord
  has_one_attached :avatar
end

How It Works:

• When you upload a file, Active Storage creates an entry in the active_storage_blobs table.
• The active_storage_attachments table links this file to the record.
• If a new file is attached, the old one is automatically replaced.

Example: Attaching and Displaying an Image

user = User.find(1)
user.avatar.attach(io: File.open("/path/to/avatar.jpg"), filename: "avatar.jpg", content_type: "image/jpeg")

# Checking if an avatar exists
user.avatar.attached? # => true

# Displaying the image in a view
<%= image_tag user.avatar.variant(resize: "100x100").processed if user.avatar.attached? %>

2. has_many_attached

Use this when a model can have multiple file attachments. For instance, a Product model may have multiple images.

Usage:

class Product < ApplicationRecord
  has_many_attached :images
end

How It Works:

• Multiple files can be attached to a single record.
• Active Storage tracks all file uploads in the active_storage_blobs and active_storage_attachments tables.
• Deleting an attachment removes it from storage.

Example: Attaching and Displaying Multiple Images

product = Product.find(1)
product.images.attach([
  { io: File.open("/path/to/image1.jpg"), filename: "image1.jpg", content_type: "image/jpeg" },
  { io: File.open("/path/to/image2.jpg"), filename: "image2.jpg", content_type: "image/jpeg" }
])

# Checking if images exist
product.images.attached? # => true

# Displaying all images in a view
<% if product.images.attached? %>
  <% product.images.each do |image| %>
    <%= image_tag image.variant(resize: "200x200").processed %>
  <% end %>
<% end %>

Benefits of Using has_one_attached & has_many_attached

1. Simplifies File Attachments – Directly associates files with Active Record models.
2. No Need for Extra Tables – Unlike some gems (e.g., CarrierWave), Active Storage doesn’t require additional tables for storing file paths.
3. Easy Cloud Storage Integration – Works seamlessly with Amazon S3, Google Cloud Storage, and Azure.
4. Variant Processing – Generates resized versions of images using variant (e.g., thumbnails).
5. Automatic Cleanup – Old attachments are automatically removed when replaced.

Final Thoughts

Active Storage in Rails 8 provides a seamless way to manage file uploads, integrating directly with models while handling storage efficiently. By understanding how it processes uploads internally, we can better optimize performance and ensure a smooth user experience.

In an upcoming blog, we’ll dive deeper into Turbo Streams and how they enhance real-time updates in Rails applications.