Easier access to the variant of a blob

lib/active_storage/blob.rb

 require "active_storage/service"
 require "active_storage/filename"
 require "active_storage/purge_job"
+require "active_storage/variant"
 
 # Schema: id, key, filename, content_type, metadata, byte_size, checksum, created_at
 class ActiveStorage::Blob < ActiveRecord::Base
@@ -40,6 +41,10 @@ def filename
     ActiveStorage::Filename.new(self[:filename])
   end
 
+  def variant(variation)
+    ActiveStorage::Variant.new(self, variation: variation)
+  end
+
   def url(expires_in: 5.minutes, disposition: :inline)
     service.url key, expires_in: expires_in, disposition: disposition, filename: filename
   end