[erlang-questions] Mnesia transform_table doesn't work

[Chaitanya Chalasani]

Hi,

When I run mnesia:transform_table/4 on a table to add a new field, the function returns {atomic, ok} but neither the schema is updated nor the records are transformed.

The transform function is written as -

transform_fields(Tname, FieldsNew) ->
  FieldsOld = mnesia:table_info(Tname, attributes),
  RecordName = mnesia:table_info(Tname, record_name),
  if
    FieldsNew == FieldsOld ->
      not_needed;
    true ->
      Transformer = make_transformer(RecordName, FieldsOld, FieldsNew),
      mnesia:transform_table(Tname, Transformer, FieldsNew, RecordName),
  end.

make_transformer(RecordName, OldFields, NewFields) ->
  fun(OldRec) ->
      list_to_tuple([RecordName|lists:map(
                             fun(NewField) ->
                                 case string:str(OldFields, [NewField]) of
                                   0 -> undefined;
                                   Pos -> element(Pos + 1, OldRec)
                                 end
                             end,
                             NewFields
                            )])
  end.

The table I was running is -
	calls          : with 2917589  records occupying 2056606274 words of mem

I am running -
	Erlang/OTP 19 [erts-8.3] [source] [64-bit] [smp:8:8] [async-threads:10] [hipe] [kernel-poll:false]

/Chaitanya