Core Data - JSON (TouchJSON) on iPhone
- by Urizen
I have the following code which seems to go on indefinitely until the app crashes. It seems to happen with the recursion in the datastructureFromManagedObject method. I suspect that this method:
1) looks at the first managed object and follows any relationship property recursively.
2) examines the object at the other end of the relationship found at point 1 and repeats the process.
Is it possible that if managed object A has a to-many relationship with object B and that relationship is two-way (i.e an inverse to-one relationship to A from B - e.g. one department has many employees but each employee has only one department) that the following code gets stuck in infinite recursion as it follows the to-one relationship from object B back to object A and so on.
If so, can anyone provide a fix for this so that I can get my whole object graph of managed objects converted to JSON.
#import "JSONUtils.h"
@implementation JSONUtils
- (NSDictionary*)dataStructureFromManagedObject:(NSManagedObject *)managedObject {
NSDictionary *attributesByName = [[managedObject entity] attributesByName];
NSDictionary *relationshipsByName = [[managedObject entity] relationshipsByName];
//getting the values correspoinding to the attributes collected in attributesByName
NSMutableDictionary *valuesDictionary = [[managedObject dictionaryWithValuesForKeys:[attributesByName allKeys]] mutableCopy];
//sets the name for the entity being encoded to JSON
[valuesDictionary setObject:[[managedObject entity] name] forKey:@"ManagedObjectName"];
NSLog(@"+++++++++++++++++> before the for loop");
//looks at each relationship for the given managed object
for (NSString *relationshipName in [relationshipsByName allKeys]) {
NSLog(@"The relationship name = %@",relationshipName);
NSRelationshipDescription *description = [relationshipsByName objectForKey:relationshipName];
if (![description isToMany]) {
NSLog(@"The relationship is NOT TO MANY!");
[valuesDictionary setObject:[self dataStructureFromManagedObject:[managedObject valueForKey:relationshipName]] forKey:relationshipName];
continue;
}
NSSet *relationshipObjects = [managedObject valueForKey:relationshipName];
NSMutableArray *relationshipArray = [[NSMutableArray alloc] init];
for (NSManagedObject *relationshipObject in relationshipObjects) {
[relationshipArray addObject:[self dataStructureFromManagedObject:relationshipObject]];
}
[valuesDictionary setObject:relationshipArray forKey:relationshipName];
}
return [valuesDictionary autorelease];
}
- (NSArray*)dataStructuresFromManagedObjects:(NSArray*)managedObjects {
NSMutableArray *dataArray = [[NSArray alloc] init];
for (NSManagedObject *managedObject in managedObjects) {
[dataArray addObject:[self dataStructureFromManagedObject:managedObject]];
}
return [dataArray autorelease];
}
//method to call for obtaining JSON structure - i.e. public interface to this class
- (NSString*)jsonStructureFromManagedObjects:(NSArray*)managedObjects {
NSLog(@"-------------> just before running the recursive method");
NSArray *objectsArray = [self dataStructuresFromManagedObjects:managedObjects];
NSLog(@"-------------> just before running the serialiser");
NSString *jsonString = [[CJSONSerializer serializer] serializeArray:objectsArray];
return jsonString;
}
- (NSManagedObject*)managedObjectFromStructure:(NSDictionary*)structureDictionary withManagedObjectContext:(NSManagedObjectContext*)moc {
NSString *objectName = [structureDictionary objectForKey:@"ManagedObjectName"];
NSManagedObject *managedObject = [NSEntityDescription insertNewObjectForEntityForName:objectName inManagedObjectContext:moc];
[managedObject setValuesForKeysWithDictionary:structureDictionary];
for (NSString *relationshipName in [[[managedObject entity] relationshipsByName] allKeys]) {
NSRelationshipDescription *description = [[[managedObject entity]relationshipsByName] objectForKey:relationshipName];
if (![description isToMany]) {
NSDictionary *childStructureDictionary = [structureDictionary objectForKey:relationshipName];
NSManagedObject *childObject = [self managedObjectFromStructure:childStructureDictionary withManagedObjectContext:moc];
[managedObject setValue:childObject forKey:relationshipName];
continue;
}
NSMutableSet *relationshipSet = [managedObject mutableSetValueForKey:relationshipName];
NSArray *relationshipArray = [structureDictionary objectForKey:relationshipName];
for (NSDictionary *childStructureDictionary in relationshipArray) {
NSManagedObject *childObject = [self managedObjectFromStructure:childStructureDictionary withManagedObjectContext:moc];
[relationshipSet addObject:childObject];
}
}
return managedObject;
}
//method to call for obtaining managed objects from JSON structure - i.e. public interface to this class
- (NSArray*)managedObjectsFromJSONStructure:(NSString *)json withManagedObjectContext:(NSManagedObjectContext*)moc {
NSError *error = nil;
NSArray *structureArray = [[CJSONDeserializer deserializer]
deserializeAsArray:[json dataUsingEncoding:NSUTF32BigEndianStringEncoding]
error:&error];
NSAssert2(error == nil, @"Failed to deserialize\n%@\n%@", [error localizedDescription], json);
NSMutableArray *objectArray = [[NSMutableArray alloc] init];
for (NSDictionary *structureDictionary in structureArray) {
[objectArray addObject:[self managedObjectFromStructure:structureDictionary withManagedObjectContext:moc]];
}
return [objectArray autorelease];
}
@end
