@chillu `GridFieldDataColumns` causes an "Uncaught Exception: Object->__call(): the method 'fortemplate' does not exist on 'ManyManyList'" exception. I think it's impossible (and completely pointless) to actually reach any of this code without having `GridFieldDataColumns` in your config. I guess you could implement your own column provider, but you'd surely still run into the same issue.

If you like I can still implement it, it should just be an extra:
```php
else if ($tmpItem instanceof RelationList) {
	// It's impossible to sort on a HasManyList/ManyManyList
	throw new Exception(__CLASS__ . ' is unable to sort on a RelationList, please only specify'
		. ' has_one relations');
}
```