MySQL/OTP + Poolboy
===================

Status: **Work in progress**. This README is written with the assumption that #2, #3, #4 and #5 are solved. Some tests should be added as well.

**MySQL/OTP + Poolboy** provides connection pooling for [MySQL/OTP](//github.com/mysql-otp/mysql-otp) using [Poolboy](//github.com/devinus/poolboy). It provides convenience functions for executing
SQL queries on a connection in a pool and lets you choose between two methods for createing
and managing connection pools:

1. Use it as a library that helps you supervise your own MySQL connection pools.
2. Use it as an application that manages its own supervisor for connection pools. 

I want to supervise my own connection pools
-------------------------------------------

Use `mysql_poolboy:child_spec/3` to get a supervisor child spec for a pool that you can use for
your own supervisor.

```Erlang
%% my own supervisor
init([]) ->
    MySqlOptions = [{user, "aladdin"}, {password, "sesame"}, {database, "test"}],
    PoolOptions  = [{size, 10}, {max_overflow, 20}],
    ChildSpecs = [
        %% MySQL pools
        mysql_poolboy:child_spec(pool1, MySqlOptions, PoolOptions),
        %% other workers...
        {some_other_worker, {some_other_worker, start_link, []},
         permanent, 10, worker, [some_other_worker]}
    ],
    {ok, {{one_for_one, 10, 10}, ChildSpecs}}.
```

Let MySQL/OTP + Poolboy supervise my pools
------------------------------------------

This approach requires you to start the application using `application:ensure_started(mysql_poolboy)` (or by letting your release tool do this for you).

Pools can be added at run-time using `mysql_poolboy:add_pool/3`.

Pools can also be created at start-up by defining configuration parameters for `mysql_poolboy`. The name of each configuration parameter is the pool name and the value is a pair on the form `{MySqlOptions, PoolOptions}`.

Example:

Start your Erlang node with `erl -config mypools.config` where mypools.config:

```Erlang
{mysql_poolboy, [
    {pool1, {[{user, "aladdin"}, {password, "sesame"}, {database, "test"}],
             [{size, 10}, {max_overflow, 20}]}
]}.
```

Using the connection pools
--------------------------

The most commonly used MySQL functions are available with wrappers in mysql_poolboy.

```Erlang
1> mysql_poolboy:query(pool1, "SELECT * FROM foo WHERE id=?", [42]).
{ok,[<<"id">>,<<"bar">>],[[42,<<"baz">>]]}
2> mysql_poolboy:execute(pool1, [42]).
{ok,[<<"id">>,<<"bar">>],[[42,<<"baz">>]]}
```

For transactions, the connection pid is passed to the transaction fun as the first parameter.

```Erlang
3> mysql_poolboy:transaction(pool1, fun (Pid) ->
       ok = mysql:query(Pid, "INSERT INTO foo VALUES (?, ?)", [1, <<"banana">>]),
       ok = mysql:query(Pid, "INSERT INTO foo VALUES (?, ?)", [2, <<"kiwi">>]),
       hello
   end).
{atomic, hello}
```

Sometimes you need to checkout a connection to execute multiple queries on it, without wrapping it in an SQL transaction. For this purpose you can use either a pair of `checkout/1` and `checking/2` or a call to `with/2` with a fun.

```Erlang
4> mysql_poolboy:with(pool1, fun (Pid) ->
       {ok, _, [[OldTz]]} = mysql:query(Pid, "SELECT @@time_zone"),
       ok = mysql:query(Pid, "SET time_zone = '+00:00'"),
       %% Do some stuff in the UTC time zone...
       ok = mysql:query(Pid, "SET time_zone = ?", [OldTz])
   end).
ok
```

License
-------

GNU Lesser General Public License (LGPL) version 3 or any later version.
Since the LGPL is a set of additional permissions on top of the GPL, both
license texts are included in the files [COPYING.LESSER](COPYING.LESSER) and
[COPYING](COPYING) respectively.