2 files changed, 21 insertions, 5 deletions
diff --git a/activestorage/lib/active_storage/attached/macros.rb b/activestorage/lib/active_storage/attached/macros.rb
index f3879ee2e3..35a081adc4 100644
--- a/activestorage/lib/active_storage/attached/macros.rb
+++ b/activestorage/lib/active_storage/attached/macros.rb
@@ -26,7 +26,7 @@ module ActiveStorage
     def has_one_attached(name, dependent: :purge_later)
       class_eval <<-CODE, __FILE__, __LINE__ + 1
         def #{name}
-          @active_storage_attached_#{name} ||= ActiveStorage::Attached::One.new("#{name}", self)
+          @active_storage_attached_#{name} ||= ActiveStorage::Attached::One.new("#{name}", self, dependent: #{dependent == :purge_later ? ":purge_later" : "false"})
         end
       CODE
 
@@ -65,7 +65,7 @@ module ActiveStorage
     def has_many_attached(name, dependent: :purge_later)
       class_eval <<-CODE, __FILE__, __LINE__ + 1
         def #{name}
-          @active_storage_attached_#{name} ||= ActiveStorage::Attached::Many.new("#{name}", self)
+          @active_storage_attached_#{name} ||= ActiveStorage::Attached::Many.new("#{name}", self, dependent: #{dependent == :purge_later ? ":purge_later" : "false"})
         end
       CODE
 
diff --git a/activestorage/lib/active_storage/attached/one.rb b/activestorage/lib/active_storage/attached/one.rb
index 2e5831348e..ac90f32d95 100644
--- a/activestorage/lib/active_storage/attached/one.rb
+++ b/activestorage/lib/active_storage/attached/one.rb
@@ -21,11 +21,14 @@ module ActiveStorage
     #   person.avatar.attach(io: File.open("~/face.jpg"), filename: "face.jpg", content_type: "image/jpg")
     #   person.avatar.attach(avatar_blob) # ActiveStorage::Blob object
     def attach(attachable)
-      write_attachment \
-        ActiveStorage::Attachment.create!(record: record, name: name, blob: create_blob_from(attachable))
+      if attached? && dependent == :purge_later
+        replace attachable
+      else
+        write_attachment create_attachment_from(attachable)
+      end
     end
 
-    # Returns true if an attachment has been made.
+    # Returns +true+ if an attachment has been made.
     #
     #   class User < ActiveRecord::Base
     #     has_one_attached :avatar
@@ -53,6 +56,19 @@ module ActiveStorage
     end
 
     private
+      def replace(attachable)
+        blob.tap do
+          transaction do
+            destroy
+            write_attachment create_attachment_from(attachable)
+          end
+        end.purge_later
+      end
+
+      def create_attachment_from(attachable)
+        ActiveStorage::Attachment.create!(record: record, name: name, blob: create_blob_from(attachable))
+      end
+
       def write_attachment(attachment)
         record.public_send("#{name}_attachment=", attachment)
       end