Publish :create, ["created", deeply_nested_item_id]

   pub_sub do
     ...
     publish :create, ["created", :chat_room_id]

   relationships do
     belongs_to :post, MyApp.Chat.Post do
       api MyApp.Chat
      ..

   aggregates do
     first  :chat_room_id, :post, :chat_room_id

** (Protocol.UndefinedError) protocol String.Chars not implemented for #Ash.NotLoaded<:aggregate> of type Ash.NotLoaded (a struct)

def chat_room_load() do
  comments =
     Comment
     |> Ash.Query.load([:post, :chat_room_id])
  posts =
     Post
     |> Ash.Query.load([
        comment: comments
        ...
         ])