ruby 51 lines · 9 steps

Validating and serving avatars with Active Storage in Rails

A Rails model attaches an image, validates its size and type, and exposes processed variants while a controller handles upload and removal.

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Rails Intermediate active storage file uploads validation image variants strong parameters
1class User < ApplicationRecord
2 has_one_attached :avatar
3 
4 validate :acceptable_avatar
5 
6 def avatar_thumbnail
7 avatar.variant(resize_to_fill: [100, 100], format: :webp).processed
8 end
9 
10 def avatar_medium
11 avatar.variant(resize_to_limit: [400, 400], format: :webp, saver: { quality: 80 }).processed
12 end
13 
14 private
15 
16 def acceptable_avatar
17 return unless avatar.attached?
18 
19 unless avatar.blob.byte_size <= 5.megabytes
20 errors.add(:avatar, "is too big (maximum is 5MB)")
21 end
22 
23 acceptable_types = %w[image/png image/jpeg image/webp]
24 unless acceptable_types.include?(avatar.blob.content_type)
25 errors.add(:avatar, "must be a PNG, JPEG, or WebP")
26 end
27 end
28end
29 
30class AvatarsController < ApplicationController
31 before_action :authenticate_user!
32 
33 def update
34 if current_user.update(avatar_params)
35 redirect_to edit_profile_path, notice: "Avatar updated."
36 else
37 render "profiles/edit", status: :unprocessable_entity
38 end
39 end
40 
41 def destroy
42 current_user.avatar.purge_later
43 redirect_to edit_profile_path, notice: "Avatar removed."
44 end
45 
46 private
47 
48 def avatar_params
49 params.require(:user).permit(:avatar)
50 end
51end
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Active Storage attachments need explicit validations since the framework won't enforce size or content type for you.
  2. 2Defining variants as model methods keeps image-processing rules in one place and reusable across views.
  3. 3Use purge_later to remove blobs asynchronously rather than blocking the request on deletion.

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