[erlang-questions] mnesia: composite keys?

Jacob Perkins <>
Fri Jan 9 23:48:13 CET 2009


> I've read[1] that mnesia doesn't support composite keys. It seems I can use
> keys made up of tuples though:
>
> ()11> mnesia:create_table(test, [{attributes, [id, data]}]).
> {atomic,ok}
> ()19> Ins = fun() -> mnesia:write({test, {a_key, 0},
> "asdfasdf"})
> end.
> #Fun<erl_eval.20.67289768>
> ()20> mnesia:transaction(Ins).
> {atomic,ok}
> ()21> R = fun() -> mnesia:read(test, {a_key, 0}) end.
> #Fun<erl_eval.20.67289768>
> ()22> mnesia:transaction(R).
> {atomic,[{test,{a_key,0},"asdfasdf"}]}
>
>
> Is tuples as keys common practice or A Really Bad Idea(tm)?
>

Tuple keys can actually be a Really Good Idea, especially with ordered_set
tables.

Jacob
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