File uploads with Active Storage in Ruby on Rails

Introduction

Active Storage helps you easily add file uploads to your Rails app. It manages storing files and linking them to your data.

You want users to upload profile pictures.

You need to attach documents to records like invoices or reports.

You want to store images for blog posts or products.

You want to handle file uploads without writing complex code.

You want to serve uploaded files securely and efficiently.

Syntax

Ruby on Rails

class User < ApplicationRecord
  has_one_attached :avatar
end

# In a form view:
<%= form_with model: @user do |form| %>
  <%= form.file_field :avatar %>
  <%= form.submit %>
<% end %>

has_one_attached is for one file per record.

Use has_many_attached if you want multiple files.

Examples

This allows an article to have many images uploaded.

Ruby on Rails

class Article < ApplicationRecord
  has_many_attached :images
end

Enables direct uploads to cloud storage for faster uploads.

Ruby on Rails

<%= form.file_field :avatar, direct_upload: true %>

Attaches the uploaded file to the user record in the controller.

Ruby on Rails

user.avatar.attach(params[:user][:avatar])

Sample Program

This example shows a User model with one attached avatar file. The form lets users pick a file to upload. The controller saves the user and attaches the file.

Ruby on Rails

class User < ApplicationRecord
  has_one_attached :avatar
end

# Controller example
class UsersController < ApplicationController
  def new
    @user = User.new
  end

  def create
    @user = User.new(user_params)
    if @user.save
      redirect_to @user, notice: "User created with avatar!"
    else
      render :new
    end
  end

  private

  def user_params
    params.require(:user).permit(:name, :avatar)
  end
end

# View (new.html.erb)
<%= form_with model: @user, local: true do |form| %>
  <%= form.label :name %>
  <%= form.text_field :name %>

  <%= form.label :avatar %>
  <%= form.file_field :avatar %>

  <%= form.submit "Create User" %>
<% end %>

Important Notes

Remember to run rails active_storage:install and migrate your database before using Active Storage.

Uploaded files are stored in a service like local disk, Amazon S3, or Google Cloud Storage configured in config/storage.yml.

Use rails server and check browser DevTools Network tab to see file upload requests.

Summary

Active Storage makes file uploads easy and secure in Rails.

Use has_one_attached or has_many_attached to link files to models.

Forms use file_field to let users pick files to upload.