RELATIONS

You can specify relations between models and navigate using that between models.

class ProductCategories extends Kwf_Model_Db
{
    protected $_table = 'product_categories';
    protected $_dependentModels = array(
        'Products' => 'Products' //The second value is the modelname
    );
}
class Products extends Kwf_Model_Db
{
    protected $_table = 'products';
    protected $_referenceMap = array(
        'Category' => array(
            'refModelClass' => 'ProductCategories',
            'column' => 'category_id',
        ),
        //alternative syntax: 'Category' => 'category_id->ProductCategories'
    );
}


//get category
$m = Kwf_Model_Abstract::getInstance('Products');
$row = $m->getRow(1);
$category = $row->getParentRow('Category');

//get products in category
$m = Kwf_Model_Abstract::getInstance('ProductCategories');
$category = $m->getRow(1);
$products = $category->getChildRows('Products');
foreach ($products as $product) {
    var_dump($product->name);
}

//create product in category
$m = Kwf_Model_Abstract::getInstance('ProductCategories');
$category = $m->getRow(1);
$product = $category->createChildRow('Products');
$product->name = 'bar';
$product->save();