Hello,
I have ProductPages which has many ProductImages.

I can get 3 random Product Page with the following code

function RandomProductPages($num=3) {
	return DataObject::get("ProductPage", "", "RAND()", "", $num);
    }

I can also get random ProductImages with the following code :)

function RandomProductImage($num=1) {
	return DataObject::get("ProductImage", "", "RAND()", "", $num);
    }

How to combine them, so that I can get 3 random product pages with 1 random image for each? :)

---- SOLVED ----

Ok, in the end I solved it. I post the code below, for future visitors :) The main product image is selected randomly from child images. You can use it for custom galleries. The key point is, this function must be created in the subclass, not in the controller. Thanks to edk for this great tip. http://silverstripe.org/general-questions/show/15631?start=8#post302895#post302895

class ProductPage extends Page {
		static $db = array(
	);

   function CoverImage($num = 1) { 
   $Data = $this->getComponents('Photos', '', 'RAND()', '', $num);
   return $Data; 
}

}

class ProductPage_Controller extends Page_Controller {
 
}