[erlang-questions] mnesia:ets/2 vs direct ets calls

[Oleksii Semilietov]

Question about mnesia:ets/3 and direct ets calls for mnesia tables.

In case of lookup (sequence calls from same node as ram replica node), what
is the benefit to use mnesia:ets instead of direct ets:lookup call?

I have single writer to DB (I have one node ram type, other replicas - disk
copies just for save data to disk somewhere) and would like do something
like this on ram node (sequence pseudo-code):

......
X = receive
       NewData#somerecord{id = TransID} ->
            case ets:lookup(Table, TransID) of
                 [#somerecord{date = undefined}] = OldData ->
                     NewDate = erlang:system_time(milli_seconds),
                     mnesia:dirty_write(OldData#somerecord{date = NewDate}),

                     {TransID, NewDate};
                  [#somerecord{date = Date}] ->
                      {TransID, Date}
                  [] ->
                       NewDate = erlang:system_time(milli_seconds),
                       mnesia:dirty_write(NewData),
                       {TransID, Date}
            end
        OtherReceive -> ...blabala....
end,
some_operation_with_x(X).



Or I should wrap this stuff to something like this?:

.....
receive
        NewData#somerecord{id = TransID} ->
               mnesia:ets(fun may_update/3, [NewData, Table, TransID]);
                OtherReceive -> ...blabala....
end,
some_operation_with_x(X).

may_update(NewData, Table, TransID) ->
            case mnesia:read(Table, TransID) of
                 [#somerecord{date = undefined}] = OldData ->
                     NewDate = erlang:system_time(milli_seconds),
                     mnesia:write(OldData#somerecord{date = NewDate}),
                     {TransID, NewDate};
                  [#somerecord{date = Date}] ->
                      {TransID, Date}
                  [] ->
                       NewDate = erlang:system_time(milli_seconds),
                       mnesia:write(NewData),
                       {TransID, Date}
            end
).



What is the benefit to wrap it to mnesia:ets?

Best regards.

-- 
Oleksii D. Semilietov
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