Fixes for Peter Easdown's category 1. don't assume each Entity name matches the Class name. 2. strip DATE_ATTR_PREFIX when deserializing dates back into NSManagedObject 3. add support for NSOrderedSet 4. use set to keep traversal history, and allow classes to opt-out with serializationObjectsToSkip

NSManagedObject+Serialization.h

@interface NSManagedObject (Serialization)

- (NSDictionary*) toDictionary;

- (void) populateFromDictionary:(NSDictionary*)dict;

+ (NSManagedObject*) createManagedObjectFromDictionary:(NSDictionary*)dict
                                             inContext:(NSManagedObjectContext*)context;

@end

NSManagedObject+Serialization.m

//
// see https://gist.github.com/pkclsoft/4958148 by Peter Easdown
// based upon http://vladimir.zardina.org/2010/03/serializing-archivingunarchiving-an-nsmanagedobject-graph/
//

#import "NSManagedObject+Serialization.h"

@implementation NSManagedObject (Serialization)

#define DATE_ATTR_PREFIX @"dAtEaTtr:"
#warning "Change CLASS_PREFIX if it's not ABC"
#define CLASS_PREFIX @"ABC"

#pragma mark -
#pragma mark Dictionary conversion methods

- (NSDictionary*) toDictionaryWithTraversalHistory:(NSMutableSet*)traversalHistory {
    NSArray* attributes = [[[self entity] attributesByName] allKeys];
    NSArray* relationships = [[[self entity] relationshipsByName] allKeys];
    NSMutableDictionary* dict = [NSMutableDictionary dictionaryWithCapacity:
                                 [attributes count] + [relationships count] + 1];

    NSMutableSet *localTraversalHistory = nil;

    if (traversalHistory == nil) {
        localTraversalHistory = [NSMutableSet setWithCapacity:[attributes count] + [relationships count] + 1];
    } else {
        localTraversalHistory = traversalHistory;
    }

    [localTraversalHistory addObject:self];

    [dict setObject:[[self class] description] forKey:@"class"];

    for (NSString* attr in attributes) {
        NSObject* value = [self valueForKey:attr];

        if (value != nil) {
            if ([value isKindOfClass:[NSDate class]]) {
                NSTimeInterval date = [(NSDate*)value timeIntervalSinceReferenceDate];
                NSString *dateAttr = [NSString stringWithFormat:@"%@%@", DATE_ATTR_PREFIX, attr];
                [dict setObject:[NSNumber numberWithDouble:date] forKey:dateAttr];
            } else {
                [dict setObject:value forKey:attr];
            }
        }
    }

    for (NSString* relationship in relationships) {
        NSObject* value = [self valueForKey:relationship];

        if ([value isKindOfClass:[NSSet class]]) {
            // To-many relationship

            // The core data set holds a collection of managed objects
            NSSet* relatedObjects = (NSSet*) value;

            // Our set holds a collection of dictionaries
            NSMutableArray* dictSet = [NSMutableArray arrayWithCapacity:[relatedObjects count]];

            for (NSManagedObject* relatedObject in relatedObjects) {
                if ([localTraversalHistory containsObject:relatedObject] == NO) {
                    [dictSet addObject:[relatedObject toDictionaryWithTraversalHistory:localTraversalHistory]];
                }
            }

            [dict setObject:[NSArray arrayWithArray:dictSet] forKey:relationship];
        }
        else if ([value isKindOfClass:[NSOrderedSet class]]) {
            // To-many relationship

            // The core data set holds an ordered collection of managed objects
            NSOrderedSet* relatedObjects = (NSOrderedSet*) value;

            // Our ordered set holds a collection of dictionaries
            NSMutableArray* dictSet = [NSMutableArray arrayWithCapacity:[relatedObjects count]];

            for (NSManagedObject* relatedObject in relatedObjects) {
                if ([localTraversalHistory containsObject:relatedObject] == NO) {
                    [dictSet addObject:[relatedObject toDictionaryWithTraversalHistory:localTraversalHistory]];
                }
            }

            [dict setObject:[NSOrderedSet orderedSetWithArray:dictSet] forKey:relationship];
        }
        else if ([value isKindOfClass:[NSManagedObject class]]) {
            // To-one relationship

            NSManagedObject* relatedObject = (NSManagedObject*) value;

            if ([localTraversalHistory containsObject:relatedObject] == NO) {
                // Call toDictionary on the referenced object and put the result back into our dictionary.
                [dict setObject:[relatedObject toDictionaryWithTraversalHistory:localTraversalHistory] forKey:relationship];
            }
        }
    }

    if (traversalHistory == nil) {
        [localTraversalHistory removeAllObjects];
    }

    return dict;
}

- (NSDictionary*) toDictionary {
    // Check to see there are any objects that should be skipped in the traversal.
    // This method can be optionally implemented by NSManagedObject subclasses.
    NSMutableSet *traversedObjects = nil;
    if ([self respondsToSelector:@selector(serializationObjectsToSkip)]) {
        traversedObjects = [self performSelector:@selector(serializationObjectsToSkip)];
    }
    return [self toDictionaryWithTraversalHistory:traversedObjects];
}

+ (id) decodedValueFrom:(id)codedValue forKey:(NSString*)key {
    if ([key hasPrefix:DATE_ATTR_PREFIX] == YES) {
        // This is a date attribute
        NSTimeInterval dateAttr = [(NSNumber*)codedValue doubleValue];

        return [NSDate dateWithTimeIntervalSinceReferenceDate:dateAttr];
    } else {
        // This is an attribute
        return codedValue;
    }
}

- (void) populateFromDictionary:(NSDictionary*)dict
{
    NSManagedObjectContext* context = [self managedObjectContext];

    for (NSString* key in dict) {
        if ([key isEqualToString:@"class"]) {
            continue;
        }

        NSObject* value = [dict objectForKey:key];

        if ([value isKindOfClass:[NSDictionary class]]) {
            // This is a to-one relationship
            NSManagedObject* relatedObject =
            [NSManagedObject createManagedObjectFromDictionary:(NSDictionary*)value
                                                     inContext:context];

            [self setValue:relatedObject forKey:key];
        }
        else if ([value isKindOfClass:[NSArray class]]) {
            // This is a to-many relationship
            NSArray* relatedObjectDictionaries = (NSArray*) value;

            // Get a proxy set that represents the relationship, and add related objects to it.
            // (Note: this is provided by Core Data)
            NSMutableSet* relatedObjects = [self mutableSetValueForKey:key];

            for (NSDictionary* relatedObjectDict in relatedObjectDictionaries) {
                NSManagedObject* relatedObject =
                [NSManagedObject createManagedObjectFromDictionary:relatedObjectDict
                                                         inContext:context];
                [relatedObjects addObject:relatedObject];
            }
        }
        else if ([value isKindOfClass:[NSOrderedSet class]]) {
            // This is a to-many relationship
            NSArray* relatedObjectDictionaries = (NSArray*) value;

            // Get a proxy set that represents the relationship, and add related objects to it.
            // (Note: this is provided by Core Data)
            NSMutableOrderedSet* relatedObjects = [self mutableOrderedSetValueForKey:key];

            for (NSDictionary* relatedObjectDict in relatedObjectDictionaries) {
                NSManagedObject* relatedObject =
                [NSManagedObject createManagedObjectFromDictionary:relatedObjectDict
                                                         inContext:context];
                [relatedObjects addObject:relatedObject];
            }
        }
        else if (value != nil) {
            if ([key hasPrefix:DATE_ATTR_PREFIX] == NO)
                [self setValue:[NSManagedObject decodedValueFrom:value forKey:key] forKey:key];
            else {
                //  the entity Transaction is not key value coding-compliant for the key "dAtEaTtr:timestamp".
                NSString *originalKey = [key stringByReplacingOccurrencesOfString:DATE_ATTR_PREFIX withString:@""];
                [self setValue:[NSManagedObject decodedValueFrom:value forKey:key] forKey:originalKey];
            }
        }
    }
}

+ (NSManagedObject*) createManagedObjectFromDictionary:(NSDictionary*)dict
                                             inContext:(NSManagedObjectContext*)context
{
    NSString* class = [dict objectForKey:@"class"];

    // strip off class prefix, if the names in our data model don't match the class names!
    NSString* name = [class stringByReplacingOccurrencesOfString:CLASS_PREFIX withString:@""];

    NSManagedObject* newObject =
    (NSManagedObject*)[NSEntityDescription insertNewObjectForEntityForName:name
                                                    inManagedObjectContext:context];

    [newObject populateFromDictionary:dict];

    return newObject;
}

@end

The date prefixing is not necessary these days, surely, since Core Data supports Date as a data type.