| Author |
Message |
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| sv75 |
 Posted: Wed Oct 24, 2007 10:37 am |
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User
Joined: 19 Oct 2007
Posts: 10
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I spent two hours reading manuals and still cannot get it working as I want. Hope somebody point me my error.
usecase: I try to run it on single node from cli and just save data on disk. That's all. Still no luck. I blame myself. Source cod, output is below:
Code:
-module(m2).
-export([start/0]).
-record(test, {id, data}).
start() ->
io:format("Node: ~w~n", [node()]),
io:format("schema: ~w~n", [mnesia:create_schema([node()])]),
ok = mnesia:start(),
io:format("create table: ~w~n", [mnesia:create_table(test,
[{disc_copies, [node()]},
{type, bag},
{attributes, record_info(fields, test)}])]),
io:format("write: ~w~n", [mnesia:transaction(
fun() -> mnesia:write(#test{id = 1, data = "aaaa"}) end)]),
stopped = mnesia:stop().
First run: everything looks ok, directory is created too:
Code:
$ erl -noshell -s m2 start -s init stop -sname node
Node: 'node@seva-work'
schema: ok
create table: {atomic,ok}
write: {atomic,ok}
Second run. It does not work:
Code:
Node: 'node@seva-work'
schema: {error,{'node@seva-work',{already_exists,'node@seva-work'}}} # fine
create table: {aborted,{already_exists,test}} # ok, fine
write: {aborted,{no_exists,test}} # but why???
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| francesco |
| Posted: Wed Oct 24, 2007 1:11 pm |
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User
Joined: 07 Jul 2006
Posts: 249
Location: London
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The second run fails because you have already created the schema and the table. They are persistent. Remove the directory created by Mnesia, and all will work as expected. Else, skip the create_schema and the create_table.
Francesco
--
http://www.erlang-consulting.com |
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| sv75 |
| Posted: Wed Oct 24, 2007 1:17 pm |
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User
Joined: 19 Oct 2007
Posts: 10
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francesco wrote: The second run fails because you have already created the schema and the table.
I wonder why 'write' fails, not 'create_*'  Sorry if it was not clean.
francesco wrote:
Else, skip the create_schema and the create_table.
skiping it does not change anything imho.
Code:
-module(m2).
-export([start/0]).
-record(test, {id, data}).
start() ->
ok = mnesia:start(),
io:format("write: ~w~n", [mnesia:transaction(
fun() -> mnesia:write(#test{id = 1, data = "aaaa"}) end)]).
Output:
Code:
$ erl -noshell -s m2 start -s init stop -sname node
write: {aborted,{no_exists,test}}
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| francesco |
| Posted: Wed Oct 24, 2007 1:41 pm |
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User
Joined: 07 Jul 2006
Posts: 249
Location: London
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Mnesia will load its existing in the background, immediately returning ok once you've called mnesia:start/0. What is probably happening is that test has not been loaded yet. Put mnesia:wait_for_tables([test]) before the write, and it should work.
Francesco
PS. Hope it is ok if I move this thread to the OTP section, as it is where it belongs
--
http://www.erlang-consulting.com |
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| sv75 |
| Posted: Wed Oct 24, 2007 1:47 pm |
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User
Joined: 19 Oct 2007
Posts: 10
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"RTFM" would be an appropirate answer...
mnesia:wait_for_tables([test], infinity)
Ok, I think I'm gonna teach some students now |
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