Subject.php

<?php

class Subject extends Nmc_Db_Table_Row
{
    protected function _init()
    {
        parent::_init();

        $departmentRelation = new Nmc_Db_Table_Relation_HasOne(
            Departments::getInstance(),
            $this,
            'department',
            'department',
            true
        );
        $this->_registerRelation($departmentRelation);
    }
}