function init()
{
parent::init();
// We must select books which are either never been borrowed or have been returned
$f = $this->join('library_borrowing.library_book_id', null, 'left')->addField('is_returned')->system(true);
// Now that our relation is defined we can add custom condition with the OR clause.
$this->addCondition($this->dsql()->orExpr()->where($f, 'is', null)->where($f, '1'));
}
function init()
{
parent::init();
$this->a = $this->join('author');
$this->a->addField('email');
$this->a->addField('birth')->type('date');
}
