如何在Magento中只获得直接儿童产品类别？

I'm looking for a way to get the direct child products of a certain category but not the products which might be in a sub-category of the category.

For the following catalog structure this means when I got Category 1 I only want Product 5 and 6.

Category 1
    Category 1.1
        Product 1
        Product 2
    Category 1.2
        Product 3
        Product 4
    Product 5
    Product 6

Everything I tried till now returned me all products including the ones from the category's sub category. So I always get Product 1 to 6

Any suggestions on that?

Here is one way...

$categoryId = 1;
$categoryProducts = Mage::getModel('catalog/product')->getCollection()
    ->joinField('category_id', 'catalog/category_product', 'category_id', 'product_id=entity_id', null, 'left')
    ->addAttributeToFilter('category_id', $categoryId)
;

Try:

Mage::getModel('catalog/product')->getCollection()->addFieldToFilter('category',value);

I don't test this because I'm away from my magento now, but might work.