Distributed Core Data - Core Data: Data Storage and Management for iOS, OS X, and iCloud - page 185

objects share a many-to-one relationship between the properties children and
parent . The resulting model looks like this:
Distributed Objects Protocol
When I am working with distributed objects, I prefer to contain the contract
between the client and the server within a protocol. For this application, we
are going to have a few methods that the clients can use to query the server,
but we are not going to have any server to client queries.
The resulting protocol is as follows:
DistributedCDServer/PPDistributedProtocol.h
#define kDomainName @ "local."
#define kServiceName @ "_pragProgExample._tcp"
@protocol PPDistributedProtocol
- (oneway void )ping;
- (byref NSManagedObject*)createObject;
- (byref NSManagedObject*)createChildForObject:(byref NSManagedObject*)parent;
- (oneway void )deleteObject:(byref NSManagedObject*)object;
- (byref NSArray*)allObjects;
- (byref NSArray*)objectsOfName:(bycopy NSString*)name
withPredicate:(bycopy NSPredicate*)predicate;
@end
When we are working with distributed objects, we need to define how nonscalar
attributes are handled. (These are discussed in depth in Apple's documenta-
tion.) In our protocol, we are passing most of the objects byref , which means
an NSDistantObject is created on the receiver as a proxy to the object residing
on the server. This is different from bycopy , which makes a copy of the object
on the receiving end. One of the interesting differences between these is that
KVO works across a distributed object when it is passed byref . This will be
demonstrated as we build the application.