<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=Windows-1252">
</head>
<body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">
<div><br>
</div>
<div>The {aborted,{node_not_running,'<a href="mailto:nit_notes@127.0.0.1">nit_notes@127.0.0.1</a>’}} message comes from mnesia, as you’re trying to run a mnesia transaction without actually having a mnesia database.</div>
<div><br>
</div>
<div>You don’t need mnesia at all to use QLC. Just execute qlc:e(Q) directly.</div>
<div><br>
</div>
<div>BR,</div>
<div>Ulf W</div>
<br>
<div>
<div>On 18 Oct 2014, at 17:46, <a href="mailto:lloyd@writersglen.com">lloyd@writersglen.com</a> wrote:</div>
<br class="Apple-interchange-newline">
<blockquote type="cite"><font face="arial" size="2">
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
Hello,</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
I really really want to understand qlc. But that's another story. Here's my immediate problem:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
I have a simple dets db that stores:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
-record(note, {date, subject, note}).</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
I want to fetch all notes equal or less than a given date. Leveraging Joe Armstrong's do/1 function (Programming Erlang, 2007, p326), I wrote a query function as so:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
do(Q) -><br>
F = fun() -> qlc:e(Q) end,<br>
{atomic, Val} = mnesia:transaction(F),<br>
Val.</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
get_notes(Date) -><br>
open_notes_db(),<br>
do(qlc:q([Record || Record <- dets:table(nit_notes), Record#note.date =< Date])),<br>
close_notes_db().</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
When I run get_notes/1, I get this:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
36> notes_store:get_notes(Date).<br>
** exception error: no match of right hand side value {aborted,{node_not_running,'<a href="mailto:nit_notes@127.0.0.1">nit_notes@127.0.0.1</a>'}}<br>
in function notes_store:do/1 (/home/lloyd/nit_host/nit_notes/site/src/notes_store.erl, line 53)<br>
in call from notes_store:get_notes/1 (/home/lloyd/nit_host/nit_notes/site/src/notes_store.erl, line 59)</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
This suggests that my dets db is not open, but I did that in get_notes/1:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
open_notes_db() -><br>
File = nit_notes,<br>
{ok, nit_notes} = dets:open_file(File,<br>
[{keypos,#note.date}, {type,bag}]).</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
Which, in the shell, returns:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
29> notes_store:open_notes_db().<br>
{ok,nit_notes}</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
If I run:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
qlc:q([Record#note.note || Record <- dets:table(nit_notes), Record#note.date =< Date ])</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
...in the shell, I get:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
{qlc_handle,{qlc_lc,#Fun<erl_eval.20.90072148>, {qlc_opt,false,false,-1,any,[],any,524288,allowed}}}</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
Yes, I know that this is a query handle. But what in world does it mean? If I plug this mess it into the shell, I get:</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
1> Q = qlc:q([Record#note.note || Record <- dets:table(nit_notes), Record#note.date =< Date ]).</div>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
2> qlc:eval(Q).</div>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
** exception error: bad argument<br>
in function dets:safe_fixtable/2<br>
called as dets:safe_fixtable(nit_notes,true)<br>
in call from qlc:call/4 (qlc.erl, line 3759)<br>
in call from qlc:table_handle/3 (qlc.erl, line 2616)<br>
in call from qlc:setup_le/3 (qlc.erl, line 2381)<br>
in call from qlc:setup_quals/6 (qlc.erl, line 2480)<br>
in call from qlc:setup_quals/4 (qlc.erl, line 2438)<br>
in call from qlc:setup_le/3 (qlc.erl, line 2377)<br>
in call from qlc:eval/2 (qlc.erl, line 290)</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
Which, again, suggests a problem with my dets table. But I don't know what.</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
Or, is it possible that my problem is with mnesia:transactions/1 in do/1? Docs do say that qlc should work with dets, but I don't see a dets:transactions/1.</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
How can I diagnose and fix?</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
Many thanks,</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
LRP</div>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<p style="margin:0;padding:0;font-family: arial; font-size: 10pt; word-wrap: break-word;">
</p>
<!--WM_COMPOSE_SIGNATURE_START-->
<div style="margin: 0px; padding: 0px; font-family: arial; font-size: 10pt; word-wrap: break-word;">
*********************************************<br>
My books:<br>
<br>
THE GOSPEL OF ASHES<br>
<a href="https://urldefense.proofpoint.com/v1/url?u=http://thegospelofashes.com&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=%2BeQ4KDUqB%2Ba5p47eZISTJX4bLLnoLmTlWbkSNWD9lg0%3D%0A&m=mjdxP7uwDg%2BWhrXf1j%2FxZNIGMHTaty7pD4Z3bARSTAw%3D%0A&s=aee5275fa83992d7a583056ea953da62c9ff2c24468282ea113bdee7560bdab7">http://thegospelofashes.com</a><br>
<br>
Strength is not enough. Do they have the courage <br>
and the cunning? Can they survive long enough to <br>
save the lives of millions? <br>
<br>
FREEIN' PANCHO<br>
http://freeinpancho.com<br>
<br>
A community of misfits help a troubled boy find his way <br>
<br>
AYA TAKEO<br>
http://ayatakeo.com<br>
<br>
Star-crossed love, war and power in an alternative <br>
universe<br>
<br>
Available through Amazon or by request from your <br>
favorite bookstore<br>
<br>
<br>
**********************************************</div>
<!--WM_COMPOSE_SIGNATURE_END--></font>_______________________________________________<br>
erlang-questions mailing list<br>
<a href="mailto:erlang-questions@erlang.org">erlang-questions@erlang.org</a><br>
http://erlang.org/mailman/listinfo/erlang-questions<br>
</blockquote>
</div>
<br>
<div apple-content-edited="true"><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; ">
<div>
<div>Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.</div>
<div><a href="https://urldefense.proofpoint.com/v1/url?u=http://feuerlabs.com&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=%2BeQ4KDUqB%2Ba5p47eZISTJX4bLLnoLmTlWbkSNWD9lg0%3D%0A&m=mjdxP7uwDg%2BWhrXf1j%2FxZNIGMHTaty7pD4Z3bARSTAw%3D%0A&s=484168ffcdb250d0d2f73cbf7b7b7ed970edffa0b5d5787913ea68164c1ef550">http://feuerlabs.com</a></div>
</div>
<div><br>
</div>
</span><br class="Apple-interchange-newline">
</div>
<br>
</body>
</html>