id attribute is now an array. (#4685)

docs/transfer_bookmarks.md

@@ -3,14 +3,14 @@
 1. Find old user_id from the User table:  
     `user_old_identifier = User.where(username: "old_identifier")`
 2. Find Bookmarks for the old user_id:  
-    `user_old_identifier_bookmarks = Bookmark.where(user_id: user_old_identifier.id)`
+    `user_old_identifier_bookmarks = Bookmark.where(user_id: user_old_identifier.ids[0])`
 3. Find the count of Bookmarks in the old user's account:
     `user_old_identifier_bookmarks.count`
 4. Find new user_id from the User table:
     `user_new_identifier = User.where(username: "new_identifier")` 
 5. Update the Bookmarks from the old user_id to new user_id:  
-    `user_old_identifier_bookmarks.each {|bookmark| bookmark.update(user_id: user_new_identifier.id)}`
+    `user_old_identifier_bookmarks.each {|bookmark| bookmark.update(user_id: user_new_identifier.ids[0])}`
 6. Confirm that the bookmarks were transferred from the old user account to the new user account:
    `user_old_identifier_bookmarks.count` should return 0
-   `user_new_identifier_bookmarks = Bookmark.where(user_id: user_new_identifier.id`
+   `user_new_identifier_bookmarks = Bookmark.where(user_id: user_new_identifier.ids[0])`
    `user_new_identifier_bookmarks.count` should be equal to `user_old_identifier_bookmarks.count`