1 files changed, 83 insertions, 0 deletions
diff --git a/activestorage/lib/active_storage/attached/one.rb b/activestorage/lib/active_storage/attached/one.rb
new file mode 100644
index 0000000000..0244232b2c
--- /dev/null
+++ b/activestorage/lib/active_storage/attached/one.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+module ActiveStorage
+  # Representation of a single attachment to a model.
+  class Attached::One < Attached
+    delegate_missing_to :attachment
+
+    # Returns the associated attachment record.
+    #
+    # You don't have to call this method to access the attachment's methods as
+    # they are all available at the model level.
+    def attachment
+      record.public_send("#{name}_attachment")
+    end
+
+    # Associates a given attachment with the current record, saving it to the database.
+    #
+    #   person.avatar.attach(params[:avatar]) # ActionDispatch::Http::UploadedFile object
+    #   person.avatar.attach(params[:signed_blob_id]) # Signed reference to blob from direct upload
+    #   person.avatar.attach(io: File.open("/path/to/face.jpg"), filename: "face.jpg", content_type: "image/jpg")
+    #   person.avatar.attach(avatar_blob) # ActiveStorage::Blob object
+    def attach(attachable)
+      if attached? && dependent == :purge_later
+        replace attachable
+      else
+        write_attachment build_attachment_from(attachable)
+      end
+    end
+
+    # Returns +true+ if an attachment has been made.
+    #
+    #   class User < ActiveRecord::Base
+    #     has_one_attached :avatar
+    #   end
+    #
+    #   User.new.avatar.attached? # => false
+    def attached?
+      attachment.present?
+    end
+
+    # Deletes the attachment without purging it, leaving its blob in place.
+    def detach
+      if attached?
+        attachment.destroy
+        write_attachment nil
+      end
+    end
+
+    # Directly purges the attachment (i.e. destroys the blob and
+    # attachment and deletes the file on the service).
+    def purge
+      if attached?
+        attachment.purge
+        write_attachment nil
+      end
+    end
+
+    # Purges the attachment through the queuing system.
+    def purge_later
+      if attached?
+        attachment.purge_later
+      end
+    end
+
+    private
+      def replace(attachable)
+        blob.tap do
+          transaction do
+            detach
+            write_attachment build_attachment_from(attachable)
+          end
+        end.purge_later
+      end
+
+      def build_attachment_from(attachable)
+        ActiveStorage::Attachment.new(record: record, name: name, blob: create_blob_from(attachable))
+      end
+
+      def write_attachment(attachment)
+        record.public_send("#{name}_attachment=", attachment)
+      end
+  end
+end