Hi, trying to use onAfterWrite to manually set the SortOrder on a dataobject since I'm not using the DOM to manage the objects, but rather using ModelAdmin.

Here's my code:

function onAfterWrite() {
		parent::onAfterWrite();
		if($this->SortOrder == 0) {
			if($prevObj = DataObject::get('Photo', '', 'Created DESC', '', 1)) {
				$sortOrder = ++$prevObj->SortOrder;
				$this->SortOrder = $sortOrder;
				$this->write();
			} else {
				$this->SortOrder = 1;
				$this->write();
			}
		}
	}

Basically what I'm trying to do is get the last created object, get its SortOrder, increment it and insert it in the new object.
This keeps setting the SortOrder to 1 (the else argument) even though the first argument should work. I tested the object getter using print_r and die, and it does correctly return the last created object. A little stumped here...

Update:

I removed the if($prevObj = DataObject::get....) part to test if it would work without checking for a previous object, but I still get the same result - the SortOrder is always set to 1.

Update #2:

Testing further with print_r, I discovered that doing this:

$obj = DataObject::get('Photo', false, 'Created DESC', false, 1);
		$sort = $obj->SortOrder;
		print_r($obj); die();

Will return the object, however when I replace $obj with $sort in the print_r, it returns nothing at all. Blank! This might be why the value keeps getting set to 1, because it's incrementing on 0 or null.

Fixed, apparently it was because using DataObject::get was returning a DataObjectSet, whereas using DataObject::get_one only returned a single object instead, allowing $obj->SortOrder to be fetched.

Final code:

function onAfterWrite() {
		parent::onAfterWrite();
		if($this->SortOrder == 0) {
			if($prevObj = DataObject::get_one('Photo', 'SortOrder > 0')) {
				$sort = ++$prevObj->SortOrder;
				$this->SortOrder = $sort;
				$this->write();
			} else {
				$this->SortOrder = 1;
				$this->write();
			}
		}
	}

I'll leave this thread open for posterity. =D