mnemosyne:string_to_handle pb !
Jens Peder Terjesen (ETO)
Jens.Peder.Terjesen@REDACTED
Tue Dec 19 14:20:29 CET 2000
Hi.
Is there an effective way to avoid queries when searching for
unequality?
Can the following query be rewritten?
Q = query [ X || X <- table ( jabber_personne ), X.age/=22 ] end,
mnesia:transaction(fun() -> mnemosyne:eval(Q) end).
Jens
-----Original Message-----
From: Ulf Wiger [mailto:etxuwig@REDACTED]
Sent: 13. desember 2000 12:19
To: Lecomte Jean François
Cc: erlang-questions@REDACTED
Subject: Re: mnemosyne:string_to_handle pb !
I cannot help you with the exact problem, except to say that
the following construct is _much_ more efficient:
mnesia_transaction(
fun() ->
P = mnesia:table_info(jabber_personne, wild_pattern),
mnesia:match_object(P#jabber_personne{age = 22})
end).
Basically, mnemosyne should be avoided for all queries, unless
you really need the cursor support, or you have very complex queries.
/Uffe
On Wed, 13 Dec 2000, Lecomte Jean François wrote:
>Hi,
>
>I do need to build a handle query using a string but when i tried to
>use the mnemosyne string_to_handle it fails !
>
>Following code
>
> Q = mnemosyne:string_to_handle( "query [ X || X <- table ( jabber_personne ), X.age=22 ] end. "),
> mnesia:transaction(fun() -> mnemosyne:eval(Q) end).
>
>gives
>
>{aborted,{function_clause,[{mnemosyne,setup_query,
> [{'EXIT',
> {function_clause,
> [{erl_parse,
> normalise,
> [{call,
> 0,
> {atom,
> 0|...},
> [{tuple|...}]}]},
> {erl_parse,normalise_list,1},
> {erl_parse,normalise,1},
> {erl_parse,normalise_list,1},
> {erl_parse,normalise,1},
> {mnemosyne_lc,
> '-one_lc_to_handle/1-fun-1-',
> 2},
> {lists,foldl,3},
> {mnemosyne_lc,
> one_lc_to_handle,
> 1}|
> more]}}]},
> {mnemosyne,cursor,2},
> {mnemosyne,eval,1},
> {mnesia_tm,apply_fun,2},
> {mnesia_tm,execute_transaction,4},
> {erl_eval,expr,3},
> {erl_eval,exprs,4},
> {shell,eval_loop,2}]}}
>
>
>
>but :
> query [ X || X <- table ( jabber_personne ), X.age=22 ] end,
> mnesia:transaction(fun() -> mnemosyne:eval(Q) end).
>
>works fine !
>
>Any idea
>
>
--
Ulf Wiger tfn: +46 8 719 81 95
Senior System Architect mob: +46 70 519 81 95
Strategic Product & System Management ATM Multiservice Networks
Data Backbone & Optical Services Division Ericsson Telecom AB
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