Track Active Storage variants in the database

actionmailbox/test/dummy/db/migrate/20180212164506_create_active_storage_tables.active_storage.rb

@@ -24,5 +24,13 @@ class CreateActiveStorageTables < ActiveRecord::Migration[5.2]
       t.index [ :record_type, :record_id, :name, :blob_id ], name: "index_active_storage_attachments_uniqueness", unique: true
       t.foreign_key :active_storage_blobs, column: :blob_id
     end
+
+    create_table :active_storage_variant_records do |t|
+      t.belongs_to :blob, null: false, index: false
+      t.string :variation_digest, null: false
+
+      t.index %i[ blob_id variation_digest ], name: "index_active_storage_variant_records_uniqueness", unique: true
+      t.foreign_key :active_storage_blobs, column: :blob_id
+    end
   end
 end

actiontext/test/dummy/db/migrate/20180212164506_create_active_storage_tables.rb

@@ -24,5 +24,13 @@ class CreateActiveStorageTables < ActiveRecord::Migration[5.2]
       t.index [ :record_type, :record_id, :name, :blob_id ], name: "index_active_storage_attachments_uniqueness", unique: true
       t.foreign_key :active_storage_blobs, column: :blob_id
     end
+
+    create_table :active_storage_variant_records do |t|
+      t.belongs_to :blob, null: false, index: false
+      t.string :variation_digest, null: false
+
+      t.index %i[ blob_id variation_digest ], name: "index_active_storage_variant_records_uniqueness", unique: true
+      t.foreign_key :active_storage_blobs, column: :blob_id
+    end
   end
 end

actiontext/test/dummy/db/schema.rb

@@ -44,6 +44,12 @@ ActiveRecord::Schema.define(version: 2019_03_17_200724) do
     t.index ["key"], name: "index_active_storage_blobs_on_key", unique: true
   end
 
+  create_table "active_storage_variant_records", force: :cascade do |t|
+    t.integer "blob_id", null: false
+    t.string "variation_digest", null: false
+    t.index ["blob_id", "variation_digest"], name: "index_active_storage_variant_records_on_blob_id"
+  end
+
   create_table "messages", force: :cascade do |t|
     t.string "subject"
     t.datetime "created_at", precision: 6, null: false
@@ -69,4 +75,5 @@ ActiveRecord::Schema.define(version: 2019_03_17_200724) do
   end
 
   add_foreign_key "active_storage_attachments", "active_storage_blobs", column: "blob_id"
+  add_foreign_key "active_storage_variant_records", "active_storage_blobs", column: "blob_id"
 end

activestorage/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Variants are tracked in the database to avoid existence checks in the storage service.
+
+    *George Claghorn*
+
 *   Deprecate `service_url` methods in favour of `url`.
 
     Deprecate `Variant#service_url` and `Preview#service_url` to instead use

activestorage/app/models/active_storage/blob/representable.rb

@@ -4,6 +4,9 @@ module ActiveStorage::Blob::Representable
   extend ActiveSupport::Concern
 
   included do
+    has_many :variant_records, class_name: "ActiveStorage::VariantRecord", dependent: false
+    before_destroy { variant_records.destroy_all if ActiveStorage.track_variants }
+
     has_one_attached :preview_image
   end
 
@@ -27,7 +30,7 @@ module ActiveStorage::Blob::Representable
   # variable, call ActiveStorage::Blob#variable?.
   def variant(transformations)
     if variable?
-      ActiveStorage::Variant.new(self, transformations)
+      variant_class.new(self, transformations)
     else
       raise ActiveStorage::InvariableError
     end
@@ -90,4 +93,9 @@ module ActiveStorage::Blob::Representable
   def representable?
     variable? || previewable?
   end
+
+  private
+    def variant_class
+      ActiveStorage.track_variants ? ActiveStorage::VariantWithRecord : ActiveStorage::Variant
+    end
 end

activestorage/app/models/active_storage/variant_record.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class ActiveStorage::VariantRecord < ActiveRecord::Base
+  self.table_name = "active_storage_variant_records"
+
+  belongs_to :blob
+  has_one_attached :image
+end

activestorage/app/models/active_storage/variant_with_record.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+class ActiveStorage::VariantWithRecord
+  WEB_IMAGE_CONTENT_TYPES = %w[ image/png image/jpeg image/jpg image/gif ]
+
+  attr_reader :blob, :variation
+
+  def initialize(blob, variation)
+    @blob, @variation = blob, ActiveStorage::Variation.wrap(variation)
+  end
+
+  def processed
+    process
+    self
+  end
+
+  def process
+    transform_blob { |image| create_or_find_record(image: image) } unless processed?
+  end
+
+  def processed?
+    record.present?
+  end
+
+  def image
+    record&.image
+  end
+
+  def url(**options)
+    image&.url(**options)
+  end
+
+  alias_method :service_url, :url
+  deprecate service_url: :url
+
+  private
+    def transform_blob
+      blob.open do |input|
+        if blob.content_type.in?(WEB_IMAGE_CONTENT_TYPES)
+          variation.transform(input) do |output|
+            yield io: output, filename: blob.filename, content_type: blob.content_type
+          end
+        else
+          variation.transform(input, format: "png") do |output|
+            yield io: output, filename: "#{blob.filename.base}.png", content_type: "image/png"
+          end
+        end
+      end
+    end
+
+    def create_or_find_record(image:)
+      @record =
+        ActiveRecord::Base.connected_to(role: ActiveRecord::Base.writing_role) do
+          blob.variant_records.create_or_find_by!(variation_digest: variation.digest) do |record|
+            record.image.attach(image)
+          end
+        end
+    end
+
+    def record
+      @record ||= blob.variant_records.find_by(variation_digest: variation.digest)
+    end
+end

activestorage/app/models/active_storage/variation.rb

@@ -58,6 +58,10 @@ class ActiveStorage::Variation
     self.class.encode(transformations)
   end
 
+  def digest
+    Digest::SHA1.base64digest Marshal.dump(transformations)
+  end
+
   private
     def transformer
       if ActiveStorage.variant_processor

activestorage/db/migrate/20170806125915_create_active_storage_tables.rb

@@ -23,5 +23,13 @@ class CreateActiveStorageTables < ActiveRecord::Migration[5.2]
       t.index [ :record_type, :record_id, :name, :blob_id ], name: "index_active_storage_attachments_uniqueness", unique: true
       t.foreign_key :active_storage_blobs, column: :blob_id
     end
+
+    create_table :active_storage_variant_records do |t|
+      t.belongs_to :blob, null: false, index: false
+      t.string :variation_digest, null: false
+
+      t.index %i[ blob_id variation_digest ], name: "index_active_storage_variant_records_uniqueness", unique: true
+      t.foreign_key :active_storage_blobs, column: :blob_id
+    end
   end
 end

activestorage/db/update_migrate/20191206030411_create_active_storage_variant_records.rb

@@ -0,0 +1,11 @@
+class AddServiceNameToActiveStorageBlobs < ActiveRecord::Migration[6.0]
+  def up
+    create_table :active_storage_variant_records do |t|
+      t.belongs_to :blob, null: false, index: false
+      t.string :variation_digest, null: false
+
+      t.index %i[ blob_id variation_digest ], name: "index_active_storage_variant_records_uniqueness", unique: true
+      t.foreign_key :active_storage_blobs, column: :blob_id
+    end
+  end
+end

activestorage/lib/active_storage.rb

@@ -63,6 +63,7 @@ module ActiveStorage
   mattr_accessor :draw_routes, default: true
 
   mattr_accessor :replace_on_assign_to_many, default: false
+  mattr_accessor :track_variants, default: false
 
   module Transformers
     extend ActiveSupport::Autoload

activestorage/lib/active_storage/engine.rb

@@ -84,6 +84,7 @@ module ActiveStorage
         ActiveStorage.binary_content_type = app.config.active_storage.binary_content_type || "application/octet-stream"
 
         ActiveStorage.replace_on_assign_to_many = app.config.active_storage.replace_on_assign_to_many || false
+        ActiveStorage.track_variants = app.config.active_storage.track_variants || false
       end
     end
 

activestorage/test/models/variant_test.rb

@@ -5,6 +5,14 @@ require "database/setup"
 require "minitest/mock"
 
 class ActiveStorage::VariantTest < ActiveSupport::TestCase
+  setup do
+    @was_tracking, ActiveStorage.track_variants = ActiveStorage.track_variants, false
+  end
+
+  teardown do
+    ActiveStorage.track_variants = @was_tracking
+  end
+
   test "variations have the same key for different types of the same transformation" do
     blob = create_file_blob(filename: "racecar.jpg")
     variant_a = blob.variant(resize: "100x100")

activestorage/test/models/variant_with_record_test.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+require "test_helper"
+require "database/setup"
+
+class ActiveStorage::VariantWithRecordTest < ActiveSupport::TestCase
+  setup do
+    @was_tracking, ActiveStorage.track_variants = ActiveStorage.track_variants, true
+  end
+
+  teardown do
+    ActiveStorage.track_variants = @was_tracking
+  end
+
+  test "generating a resized variation of a JPEG blob" do
+    blob = create_file_blob(filename: "racecar.jpg")
+    variant = blob.variant(resize: "100x100")
+
+    assert_difference -> { blob.variant_records.count }, +1 do
+      variant.process
+    end
+
+    assert_match(/racecar\.jpg/, variant.url)
+
+    image = read_image(variant.image)
+    assert_equal 100, image.width
+    assert_equal 67, image.height
+
+    record = blob.variant_records.last
+    assert_equal variant.variation.digest, record.variation_digest
+  end
+
+  test "serving a previously-generated resized variation of a JPEG blob" do
+    blob = create_file_blob(filename: "racecar.jpg")
+
+    assert_difference -> { blob.variant_records.count } do
+      blob.variant(resize: "100x100").process
+    end
+
+    variant = blob.variant(resize: "100x100")
+
+    assert_no_difference -> { blob.variant_records.count } do
+      variant.process
+    end
+
+    assert_match(/racecar\.jpg/, variant.url)
+
+    image = read_image(variant.image)
+    assert_equal 100, image.width
+    assert_equal 67, image.height
+  end
+end

guides/source/configuring.md

@@ -889,12 +889,19 @@ text/javascript image/svg+xml application/postscript application/x-shockwave-fla
 
 * `config.active_storage.replace_on_assign_to_many` determines whether assigning to a collection of attachments declared with `has_many_attached` replaces any existing attachments or appends to them. The default is `true`.
 
+* `config.active_storage.track_variants` determines whether variants are recorded in the database. The default is `true`.
+
 * `config.active_storage.draw_routes` can be used to toggle Active Storage route generation. The default is `true`.
 
 ### Results of `config.load_defaults`
 
 `config.load_defaults` sets new defaults up to and including the version passed. Such that passing, say, '6.0' also gets the new defaults from every version before it.
 
+#### For '6.1', new defaults from previous versions below and:
+
+- `config.active_record.has_many_inversing`: `true`
+- `config.active_storage.track_variants`: `true`
+
 #### For '6.0', new defaults from previous versions below and:
 
 - `config.autoloader`: `:zeitwerk`

railties/lib/rails/application/configuration.rb

@@ -159,6 +159,10 @@ module Rails
           if respond_to?(:active_record)
             active_record.has_many_inversing = true
           end
+
+          if respond_to?(:active_storage)
+            active_storage.track_variants = true
+          end
         else
           raise "Unknown version #{target_version.to_s.inspect}"
         end

railties/lib/rails/generators/rails/app/templates/config/initializers/new_framework_defaults_6_1.rb.tt

@@ -8,3 +8,6 @@
 
 # Support for inversing belongs_to -> has_many Active Record associations.
 # Rails.application.config.active_record.has_many_inversing = true
+
+# Track Active Storage variants in the database.
+# Rails.application.config.active_storage.track_variants = true