could not update rails model

Question

class Student < CouchRest::Model::Base
   collection_of :phones
   def add_phone(new_phone)
     #this does not work
     #new_phone_ids_list = phone_ids << new_phone.id 
     #this works
     new_phone_ids_list = phone_ids + [new_phone.id]
     self.update_attributes(:phone_id => new_phone_ids_list)
   end
end

The difference is when I use phone_ids << new_phone.id to create a new list and update couchdb, it doesn't work. But if I use phone_ids + [new_phone.id] ,updates will work. I understand phone_ids + [new_phone.id] will return a new instance, but cannot figure out why phone_ids << new_phone.id doesnt work

Answer 1

From the documentation:

Any manual changes made to the collection ids property (group_ids), unless replaced, will require a reload of the CollectionOfProxy for the two sets of data to be in sync

http://www.rubydoc.info/github/couchrest/couchrest_model/CouchRest%2FModel%2FAssociations%2FClassMethods%3Acollection_of