NSExpressionDescription objects represent a special property description type intended for use with the
- iOS 3.0+
- macOS 10.6+
- tvOS 3.0+
- watchOS 2.0+
NSExpressionDescription describes a column to be returned from a fetch that may not appear directly as an attribute or relationship on an entity. Examples might include
max(attribute). You cannot set an
NSExpressionDescription object as a property of an entity.