Ejabberd module with child process

I created a logging module which logs messages to a mysql db, the current code is located here: https://github.com/amiadogroup/mod_log_chat_mysql5/blob/master/src/mod_log_chat_mysql5.erl

The Problem with the current code is, that sometimes the connection gets closed and as a result, the module doesn't work anymore. As you see in the code, I store the DBRef in an ets table, which is not really the good way to go.

I asked the erlang mailinglist about this and they suggested me to do the DB Connection as an own child process of the module. This would enable the module to gracefully restart the connection upon closing of the connection.

Now my question is: how can I implement this child process with gen_server and/or gen_mod?

Do I need to create two files or can I do it within the same file?

Is there any example somewhere on how I could achieve that?

Edit: As you can see in the linked github repo, I updated the code and it works now, weeha! Looking at the mod_Archive code helped me a lot, although I didn't decide to upgrade my ejabberd version.

I ran into another, but related problem now. In the code you see that I do an initial query with "SET NAMES UTF8" to prevent garbling of messages. It seems that this isn't done again if the gen_server does a reconnect. Is there any hook I can call upon reconnect so that the UTF8 query is done everytime?

Edit#2: Now I switched to E开发者_如何学运维mysql (https://github.com/Eonblast/Emysql) and it works out of the box by specifying the encoding directly on connect. Code is on github.

Thanks for your help, Michael

I suggest you look into general Erlang/OTP principles (gen_server, supervisor, etc). ejabberd is relying on this standard Erlang architecture pattern.

Regarding your comment on database, ejabberd has its own way on managing database and passing queries to MySQL for example. You should as well look into it.

In your source code you are only applying the gen_mod behaviour, if you do wish to have a gen_server you can do it in the same module, if you define the gen_server behaviour has well.

A good example would be the ejabberd module mod_archive, which implements both behaviours.

Edit: I never really worked "directly" with mysql on erlang. But through the ejabberd methods I find it pretty "easy"(you will have to make a few setup, but rather easy). You have the method

ejabberd_odbc:sql_query_t(Query)

And has an example you can find it on the module mod_archive_odbc.

To use that method(and the last module) I haved downloaded the mysql native driver and put the beams created from the driver in ejabberd ebin dir (you can put it anywhere has long is on the erlang path). A a soft link to the ejabberd ebin is my favorite:

ln -s <diryouhavethedriver>/ebin/*.beam /usr/lib/ejabberd/ebin/

and do a few configurations on you ejabberd.cfg. This process is described on this page on process one. Notice that the full steps are to make mysql the full database of ejabberd. You may not want that, so you must jump a few steps. Hope this help.