8 June 2010 at 10:03pm
Explaination - DataObject::get returns a set. When you have a set of objects you can't call methods, fields on the set since they exist on the objects in the set and not the set itself.
DataObject::get('SiteTree'); - returns a set of all SiteTree objects (pages)
DataObject::get_one('SiteTree'); - returns a object - the first SiteTree object
DataObject::get_by_id('SiteTree', $id); - returns a object - the SiteTree object with the ID = $id;