===== Creating And Running Migrations ====
==== Creating A Migration ====
A migration uses an installer file. The one illustrated here is app/installers/refmt_installer.php.  It is used to illustrate ActiveRecord's ability to maintain several languages in a database table.<code php>
<?php
class RefmtInstaller extends AkInstaller
{
    function up_1()
    {
        $this->createTable('mono_langs', "
            id,
            lang,
            name
        ");

        $this->createTable('multi_langs', "
            id,
            en_name,
            fi_name,
            sv_name
        ");
    }

    function down_1()
    {
        $this->dropTable('mono_langs','multi_langs');
    }
}
?>
</code>
==== Running a migration ====
In a terminal window, change the directory to the top of your project.  Then enter<code>
./script/migrate Refmt install
</code>
"Refmt" is the part of the class name before "Installer".
If the tables don't exist, they will be created; if they do exist, they won't be overwritten.

The significant thing here that makes the use of this file a migration is that you may add additional up and down functions to add tables, indices, columns, etc.  A down function should always undo what the corresponding up function does.  ActiveRecord keeps track of where you are in your migration.  The first time you do an install, up_1() will be executed.  If you then do an uninstall, down_1() will be executed.  Each successive install will cause the succeeding up_x() to be run (where x increments the previous up function by 1).

Let's say that you have functions up_1(), down_1(), up_2(), and down_2().  The first time you execute<code>
./script/migrate Refmt install
</code>
function up_1() will be executed.  The second time you run it, function up_2() will be executed.  If you execute<code>
./script/migrate Refmt uninstall
</code>
at this point, function down_2() will be executed.  The condition of your tables should be as defined in function up_1().  You may add as many up_x() and down_x() functions as you need to, incrementing x by 1 each time.