Magento collection filtering 嵌套where条件的简单写法

$_collection->addFieldToFilter(‘min_weight‘, array(‘lt‘ => $weight))
->addFieldToFilter(‘max_weight‘, array(‘gteq‘ => $weight));

$_collection->addFieldToFilter(
array(‘min_weight‘,‘max_weight‘),
    array(
        array(‘gt‘ => $weight),
        array(‘lt‘ => $weight)
    )
);    

$_collection->addFieldToFilter(‘min_weight‘, array(‘lt‘ => $weight))
->addFieldToFilter(
    array(‘max_weight‘,‘max_weight‘),
    array(
        array(‘gteq‘ => $weight, ‘notnull‘ => true),
        array(‘null‘ => true)
    )
);