Is it posible to conditionally disable NSValueTransformer for NSManagedObject attribute?

Question

Specifically, say I have an NSManagedObject with a "statusCode" attribute set to transformable, and a reversible value transformer subclass to covert from NSStrings to NSNumbers and vice versa. The idea is to use the value transformer so that I receive JSON and a string from a "status" key in the JSON automatically maps to an NSNumber that represents that status code in an NSManagedObject. Conversely if I were to upload the NSManagedObject to a server, at that point its status attribute would be transformed from an NSNumber to a string for the JSON.

So far so good. But, what if I also want to be able to get a simple int out of the NSManagedObjec's status property, so that I can AND it with enums in code? That is, I'd lie to cover 3 cases:

1. myManagedObject.status = [JSONResponse valueForKey:@"status"] (should use transformer to do NSString -> NSNumber)
2. [JSONforUpload setValue:myManagedObject.status forKey:@"status"] (should use transformer to do NSNumber->NSString)
3. From elsewhere in code, anything along the lines of: if(myManagedObject.status & statusInProgress) ... where statusInProgress is an enum.

I'm thinking I could temporarily disable the value transformer, however I have no idea if the NSManagedObject has a reference to it, or if I should disable it from the NSValueTransformer class, which apparently keeps a table of registered transformers?

I know that for the 3rd case I could just do [myManagedObject.status intValue] and then do the bitwise comparison, but I'm wondering if there's any way I can have the intValue] be returned automagically, from the user of this object's point of view.

Any ideas?

Answer 1

One approach would be to add a property to the transformer so that it switches between string and enum reversed values. That would work, though I ended up doing a enum<->string transformer and not using it over a transformable attribute (instead I left the managed object's attribute as int) but rather instantiating it only for the JSON <-> object conversion. After that, throughout code I just use the int attribute as is.

Answer 2

Why don't you just write two additional methods for the JSON transform and leave the property as integer? Then you'd have the best from both worlds.

Answer 3

Assuming that this entity has its own distinct managed object subclass, you could also simply add another pair of accessor methods to the class to encapsulate the conversion between NSNumber and int values. (Or add a transient attribute, if it needs to be part of the model. But you'd still need to write custom accessors to synch up the values.)