[erlang-questions] mnesia: composite keys?

Viktor Sovietov <>
Wed Jan 14 01:21:46 CET 2009



On Jan 10, 9:10 pm, Paul Mineiro <> wrote:
> On Fri, 9 Jan 2009, Viktor Sovietov wrote:
> > If you use ordered_set tables that tuple keys are useful, because you
> > can organize hierarchies inside one table. In other hand, you can't
> > save such tables on disk, so... Anyway, Erlang isn't MUMPS, so you
> > simply have not any mechanism to operate with complex keys.
>
> I have a nonstandard extension to mnesia that allows one to define new
> table types, plus a disk-based ordered set table so defined.
>
> http://code.google.com/p/mnesiaex/
>
> Also we use tuples as keys extensively in our application.


I found this useful as well, I use it with tcerl, but again, there
still is no mechanism to navigate index trees efficiently :
( Unfortunately.

Sincerely,

--Victor

>
> -- p
>
>
>
>
>
>
>
> > Sincerely,
>
> > --Victor
>
> > On Jan 9, 11:45 pm, Peter Sabaini <> wrote:
> > > Hello list,
>
> > > 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)?
>
> > > thx,
> > > peter.
>
> > > [1]http://www.erlang.org/pipermail/erlang-questions/2008-February/032903...
>
> > >  signature.asc
> > > < 1KViewDownload
>
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