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| mikl at club-internet.fr |
 Posted: Sun Apr 25, 1999 12:48 pm |
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Guest
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Hi,
I have got a question about an error in my mnesia queries.
When I try to make a joint query on two tables I get this error message
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=ERROR REPORT==== 25-Apr-1999::14:38:23 ===
!!! Error in process <0.188.0> on node 'master_at_win' with exit value:
nocatch
** exited: nocatch **
The code I am using for this query is :
task(User) ->
Q = query
[ T ||
T <- table(tasks),
U <- table(users),
U.id = User,
T.user_id = U.id ]
end,
F = fun() -> mnemosyne:eval(Q) end,
mnesia:transaction(F).
The data is the database seems correct. When I make a simple query, the
function is working, but I did not manage to make this two tables query
to work.
Do you have any clue on what I am doing wrong ?
Thank you in advance.
Mickael Remond
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| tobbe at serc.rmit.edu.au |
| Posted: Sun Apr 25, 1999 10:28 pm |
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Guest
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Shouldn't you use the Boolean test operator for equality ?
That is:
task(User) ->
Q = query
[ T ||
T <- table(tasks),
U <- table(users),
U.id == User,
T.user_id == U.id ]
end,
F = fun() -> mnemosyne:eval(Q) end,
mnesia:transaction(F).
/Tobbe
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| mikl at club-internet.fr |
| Posted: Mon Apr 26, 1999 6:12 am |
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| hakan at erix.ericsson.se |
| Posted: Mon Apr 26, 1999 7:04 am |
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Guest
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mikl>I suspect a misconfiguration, but I did not see what I a missing.
I think that you forgot to start the mnemosyne application.
The attached example worked for me, when Mnemosyne was started.
~> erl
Erlang (BEAM) emulator version 4.8.1
=20
Eshell V4.8.1 (abort with ^G)
1> c(memo().
** 1: syntax error before: '.' **
1> c(memo).=20
./memo.erl:27: Warning: non-recommended option 'export_all' used
{ok,memo}
2> memo:init().
ok
3> memo:task(hakan). =20
{atomic,[{tasks,drink_coffee,hakan}]}
4> application:stop(mnemosyne).
=20
=3DINFO REPORT=3D=3D=3D=3D 26-Apr-1999::08:54:17 =3D=3D=3D
=09application: mnemosyne
=09exited: stopped
=09type: temporary
ok
5> memo:task(hakan). =20
=20
=3DERROR REPORT=3D=3D=3D=3D 26-Apr-1999::08:54:19 =3D=3D=3D
<0.25.0> error: nocatch in mnemosyne_lc:the_query/1
** exited: nocatch **
=20
Regards
=09H=E5kan
-------------------------------------+------------------------------------
H=E5kan Mattsson, | +46 8 719 9452
Computer Science Laboratory | hakan_at_erix.ericsson.se
Ericsson Network Core Products | http://www.ericsson.se/cslab/~hakan
Box 1505, SE-126 25 Stockholm Sweden |
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