anchor.diff:  -spec get(id(), non_neg_integer()) ->
       {ok, fslogic_blocks:blocks()} | {error, term()}.
   get(Key, Num) ->
  -    DocKey = <<Key/binary, Num/integer>>,
  -    case datastore_model:get(?CTX, DocKey) of
  +    case datastore_model:get(?CTX, get_doc_key(Key, Num)) of
           {ok, #document{value = #file_local_blocks{
               blocks = Blocks, last = Last
           }}} ->
  
positive.code:         _ -> {{Blocks, []}, true}
      end,
  
      DocKey = <<Key/binary, Num/integer>>,
      Diff = fun
          (_) ->
              {ok, #file_local_blocks{
  
negative.code:             {ok, []};
          Other ->
              Other
      end.
  
  get_doc_key(Key, Num) ->
      datastore_key:build_adjacent(<<Num/integer>>, Key).
  