To attach multiple images to a Product model in Rails 8, Active Storage provides the best way using has_many_attached. Below are the steps to set up multiple image attachments in a local development environment.
1️⃣ Install Active Storage (if not already installed)
We have already done this step if you are following this series. Else run the following command to generate the necessary database migrations:
rails active_storage:install
rails db:migrate
This will create two tables in your database:
active_storage_blobs → Stores metadata of uploaded files.
active_storage_attachments → Creates associations between models and uploaded files.
2️⃣ Update the Product Model
Configuring specific variants is done the same way as has_one_attached, by calling the variant method on the yielded attachable object:
add in app/models/product.rb:
class Product < ApplicationRecord
has_many_attached :images do |attachable|
attachable.variant :normal, resize_to_limit: [540, 720]
attachable.variant :thumb, resize_to_limit: [100, 100]
end
end
You just have to mention the above and rails will create everything for you!
Variants rely on ImageProcessing gem for the actual transformations of the file, so you must add gem "image_processing" to your Gemfile if you wish to use variants.
By default, images will be processed with ImageMagick using the MiniMagick gem, but you can also switch to the libvips processor operated by the ruby-vips gem.
3️⃣ Configure Active Storage for Local Development
By default, Rails stores uploaded files in storage/ under your project directory.
Ensure your config/environments/development.rb has:
config.active_storage.service = :local
And check config/storage.yml to ensure you have:
local:
service: Disk
root: <%= Rails.root.join("storage") %>
This will store the uploaded files in storage/.
4️⃣ Add File Uploads in Controller
Modify app/controllers/products_controller.rb to allow multiple image uploads:
class ProductsController < ApplicationController
def create
@product = Product.new(product_params)
if @product.save
redirect_to @product, notice: "Product was successfully created."
else
render :new
end
end
private
def product_params
params.require(:product).permit(:name, :description, images: [])
end
end
Notice images: [] → This allows multiple images to be uploaded.
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:
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
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.
Attach Images Efficiently: Use has_one_attached or has_many_attached for file associations in models.
Avoid Serving Files via Rails: Use a CDN or proxy service to serve images instead of relying on Rails controllers.
Clean Up Unused Blobs: Regularly remove orphaned blob records using ActiveStorage::Blob.unattached.destroy_all.
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.
👉 Purpose: This table allows a single file to be attached to multiple records without duplicating the file itself.
Why Does Rails Need Both Tables?
Separation of Concerns:
active_storage_blobstracks the files themselves.
active_storage_attachmentslinks them to models.
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.
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:
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:
has_one_attached – For a single file attachment.
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
Simplifies File Attachments – Directly associates files with Active Record models.
No Need for Extra Tables – Unlike some gems (e.g., CarrierWave), Active Storage doesn’t require additional tables for storing file paths.
Easy Cloud Storage Integration – Works seamlessly with Amazon S3, Google Cloud Storage, and Azure.
Variant Processing – Generates resized versions of images using variant (e.g., thumbnails).
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.
The Rails Drop 