mnesia db dir

Ulf Wiger (AL/EAB) <>
Sun Jul 10 17:45:58 CEST 2005

Róbert Balogh wrote:
> The first question is it possible to set the path of the 
> mnesia db from "code". I mean is there other way than erl 
> -sname nodename -mnesia dir '"dirpath"'?

You can use application:set_env(mnesia, dir, "...").

You should do this after loading the mnesia application,
but before starting it.

This is not something you should make a habit out of. 
application:set_env/3 is mainly there for software upgrade.
A more structured way to do it (if you don't want to pass
it as a command-line parameter) is to use a sys.config 
file. This is when you use the sasl framework to start
your system.

> I wrote a small code for learning mnesia and I take a big 
> "discovery". It's not possible to insert any record in the 
> table, if the table name is different that the name of his record. 
> Here is my example:

You can use the option {record_name, rPerson} when creating
the table. Mnesia will then verify that all objects inserted
in 'table' are of the type #rPerson{} (as defined by the 
combination of the 'record_name' and 'attributes' options.


> -module(ex_mnesia).
> -export([start/0]).
> -export([insert/1]).
> -record(rPerson,{name = [],
>                 city = []}).
> start()->
>     mnesia:create_schema([node()]),
>     mnesia:start(),
> mnesia:create_table(table,[{attributes,record_info(fields,rPerson)},
>                                 {disc_copies,[node()]}]).
> insert(Value)->
>     Fun = fun()->
>             mnesia:write(table,#rPerson{name = Value},write)
>           end,
>     mnesia:transaction(Fun).
> After calling insert I got this in the erlang shell:
> ()5> ex_mnesia:insert(aa).
> {aborted,{bad_type,{rPerson,aa,[]}}}
> If I change the name of table to rPerson it's possible to 
> insert records in the table. So is that true that no way to 
> set different name the table as his record name or I did 
> something wrong?
> Here is what I got after change table name:
> ()3> ex_mnesia:insert(aa).
> {atomic,ok}
> thanks a lot the answers,
> br,
> /Robi

More information about the erlang-questions mailing list