Snapshotting saves object state
From EOFWiki
Code
#import <Foundation/Foundation.h> #import <EOControl/EOControl.h> @interface NSMutableDictionary ( EOEnterpriseObjectAdditions) @end @implementation NSMutableDictionary ( EOEnterpriseObjectAdditions) - (void) updateFromSnapshot:(NSDictionary *) snapshot { [self removeAllObjects]; [self addEntriesFromDictionary:snapshot]; } - (NSDictionary *) snapshot { return( [[self copy] autorelease]); } @end int main (int argc, const char * argv[]) { NSAutoreleasePool *pool; EOEditingContext *context; NSMutableDictionary *obj; pool = [NSAutoreleasePool new]; context = [[EOEditingContext new] autorelease]; obj = [NSMutableDictionary dictionary]; [context insertObject:obj]; NSLog( @"A) %@", [context currentEventSnapshotForObject:obj]); [obj willChange]; NSLog( @"B) %@", [context currentEventSnapshotForObject:obj]); [obj setObject:@"1" forKey:@"club"]; NSLog( @"C) %@", [context currentEventSnapshotForObject:obj]); [obj willChange]; NSLog( @"D) %@", [context currentEventSnapshotForObject:obj]); [obj setObject:@"2" forKey:@"club"]; NSLog( @"E) %@", [context currentEventSnapshotForObject:obj]); [context processRecentChanges]; NSLog( @"F) %@", [context currentEventSnapshotForObject:obj]); [obj willChange]; NSLog( @"G) %@", [context currentEventSnapshotForObject:obj]); [obj setObject:@"3" forKey:@"club"]; NSLog( @"H) %@", [context currentEventSnapshotForObject:obj]); [pool release]; return( 0); }
Comment
Two methods have been added to NSMutableDictionary, that are defined by the EOEnterpriseObject protocol: snapshot and updateFromSnapshot:. These methods translate the state of an object back and from an NSDictionary. During the first willChange the EOEditingContext takes a snapshot of the object, to track the state before changes were applied. Multiple edits are coalesced until processRecentChanges is invoked.
So a snapshot of the object is only taken twice in this scenario by the EOEditingContext, although there are three edits.
Output
A) {}
B) {}
C) {}
D) {}
E) {}
F) { club = 2; }
G) { club = 2; }
H) { club = 2; }
