shah743 · January 25, 2021 05:27 · May 21, 2020
diff --git a/active_storage_cheatsheet.md b/active_storage_cheatsheet.md
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+# Rails Active Storage Cheatsheet
+
+- [Rails Active Storage Cheatsheet](#rails-active-storage-cheatsheet)
+  - [Install Active Storage](#install-active-storage)
+  - [Usage](#usage)
+    - [Model](#model)
+    - [Controller](#controller)
+    - [Views (in ERB)](#views-in-erb)
+    - [Display Image and its variants or Preview (PDF or Video)](#display-image-and-its-variants-or-preview-pdf-or-video)
+      - [Install this libraries first](#install-this-libraries-first)
+      - [Display an image (when document is an image)](#display-an-image-when-document-is-an-image)
+      - [Generate a variant of an image with `variant`](#generate-a-variant-of-an-image-with-variant)
+      - [Generate a preview with `preview`](#generate-a-preview-with-preview)
+      - [Don't know the type of document? Use `representation`](#dont-know-the-type-of-document-use-representation)
+    - [Content type and size](#content-type-and-size)
+    - [Attach a local file](#attach-a-local-file)
+    - [Validation with activestorage-validator gem](#validation-with-activestorage-validator-gem)
+    - [Select all records with an attachment](#select-all-records-with-an-attachment)
+
+---
+
+## Install Active Storage
+
+Only for Rails version 5.2 and up (Rails 5.2.X & Rails 6.X.X).
+
+1. Install
+
+```sh
+rails active_storage:install
+```
+
+1. Run migration
+
+```sh
+rails db:migrate
+```
+
+## Usage
+
+We will use User model with attachment(s) name document(s), this document can be an image or PDF or video or any other type.
+
+### Model
+
+- **One attachment**
+
+```ruby
+class User < ApplicationRecord
+
+  has_one_attached :document
+end
+```
+
+- **Many attachments**
+
+```ruby
+class User < ApplicationRecord
+
+  has_many_attached :documents
+end
+```
+
+### Controller
+
+- **One attachment**
+
+```ruby
+class UsersController < ApplicationController
+  # your controller methods (index, show ...).
+  private
+
+  # Only allow a list of trusted parameters through.
+  def user_params
+    params.require(:yser).permit(:first_name, :last_name, :document)
+  end
+end
+```
+
+- **Many attachments**
+
+```ruby
+class UsersController < ApplicationController
+  # your controller methods (index, show ...).
+  private
+
+  # Only allow a list of trusted parameters through.
+  def user_params
+    params.require(:user).permit(:first_name, :last_name, documents: [])
+  end
+end
+```
+
+### Views (in ERB)
+
+Form filed:
+
+- **One attachment**
+
+```erb
+<%= form.file_field :document %>
+```
+
+- **Many attachments**
+
+```erb
+<%= form.file_field :documents, multiple: true %>
+```
+
+### Display Image and its variants or Preview (PDF or Video)
+
+#### Install this libraries first
+
+First to generate **variants** and **previews** of PDFs and videos, you will need to :
+
+1. Add `gem 'image_processing', '~> 1.2'` to your Gemfile.
+2. Install [MiniMagick](https://imagemagick.org/script/download.php) for image variants.
+3. To generate previews of PDFs, install [Poppler](https://poppler.freedesktop.org).
+4. To generate previews of Videos, install [FFmpeg](https://www.ffmpeg.org/download.html).
+
+#### Display an image (when document is an image)
+
+To check if there is an image attached before displaying it use:
+
+```ruby
+if user.documents.attached?
+```
+
+- **One attachment**
+
+```erb
+<% if user.document.attached? %>
+  <%= image_tag user.document %>
+<% end %>
+```
+
+- **Many attachments**
+
+At least one document is attached
+
+```erb
+<% if user.documents.attached? %>
+  <% user.documents.each do |document| %>
+    <%= image_tag document %>
+  <% end %>
+<% end %>
+```
+
+#### Generate a variant of an image with `variant`
+
+Don't forget `user.document` should be an **image** in this case.
+
+```erb
+<%= image_tag user.document.variant(resize_to_limit: [75, 75]).processed %>
+```
+
+> `.processed` method will store the variant for performance reasons.
+
+For more variant transformations check [image_processing docs](https://github.com/janko/image_processing#installation).
+
+#### Generate a preview with `preview`
+
+For PDFs or videos.
+
+```erb
+<% if user.document.previewable? %>
+  <%= image_tag(user.document.preview(resize: '200x200') %>
+<% end %>
+```
+
+> `.previewable?` method will check if you can create a preview of the document attached.
+
+#### Don't know the type of document? Use `representation`
+
+```erb
+<% if user.document.representable? %>
+  <%= image_tag(user.document.representation(resize: '200x200') %>
+<% end %>
+```
+
+> `.representable?` method will check if you can create a preview or a variant of the document attached.
+
+### Content type and size
+
+Document attachment content type:
+
+```ruby
+user.document.content_type
+```
+
+Video attachment file size:
+
+```ruby
+user.video.byte_size
+```
+
+### Attach a local file
+
+In tests for example we want to be able to save/attach local files in Active Storage.
+
+```ruby
+user.picture.attach(io: File.open('/path/to/file'), filename: 'my_picture.png')
+```
+
+### Validation with activestorage-validator gem
+
+To install [activestorage-validator](https://github.com/aki77/activestorage-validator) gem add in your application's Gemfile:
+
+```ruby
+gem 'activestorage-validator'
+```
+
+To use this gem, in your model add:
+
+```ruby
+class User < ApplicationRecord
+  has_one_attached :avatar
+  has_many_attached :photos
+
+  validates :avatar, presence: true, blob: { content_type: :image } # supported options: :image, :audio, :video, :text
+  validates :photos, presence: true, blob: { content_type: ['image/png', 'image/jpg', 'image/jpeg'], size_range: 1..5.megabytes }
+  # validates :photos, presence: true, blob: { content_type: %r{^image/}, size_range: 1..5.megabytes }
+end
+```
+
+### Select all records with an attachment
+
+From the comment in this [issue](https://github.com/rails/rails/issues/32295#issuecomment-374304126) in Rails repository in Github.
+
+```ruby
+# Assuming a model defined like so:
+class Post < ApplicationRecord
+  has_one_attached :image
+end
+
+# ...you can join against :image_attachment to select posts having attached images:
+Post.joins(:image_attachment).where('published_at >= ?', Time.now)
+```
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