URL to MPMediaItem

I have a simple question but I can't find the right answer. I have a song url saved to my database in a path like this.

aSound.path = [[item valueForProperty: MPMediaItemPropertyAssetURL] absoluteString];

How to convert back to a MPMediaItem object which has songname artist and artwork?

Is it possible?

Saving:

    NSNumber* persistentID = 
[mediaItem valueForProperty:MPMediaItemPropertyPersistentID];

Loading:

            MPMediaPropertyPredicate * predicate = 
              [MPMediaPropertyPredicate 
                predicateWithValue:persistentID 
                       forProperty:MPMediaItemPropertyPersistentID];

Another example: NSNumber for MPMediaItemPropertyPersistentID to NSString and back again

Note song URLs are are unreliable because any DRM song returns a null url