Where to implement NSValueTransformer for Core Data in Swift

Question

I\'m trying to put entities in a Core Data store that each have non-standard data types - one is an NSDocument and the other is an NSURL. I get that within the .xcdatamodeld I n

Answer 1

The "where" is just anywhere in your project. Anywhere that ensures that your NSValueTransformer subclass will exist at run time. Implement the NSValueTransformer subclass, and enter the class name in the Core Data model as the value transformer.

However there is a default transformer. Any class that adopts the NSCoding protocol can be automatically transformed by Core Data. In that case you mark the attribute as transformable but don't include a class name. This includes NSURL, so you don't need to transform that or convert it to a string.

For your NSDocument subclass then, you have the option of either implementing NSCoding in the class or of implementing an NSValueTransformer subclass for the document type.