核心数据-iPhone上的JSON（TouchJSON）

我有下面的代码，它似乎一直持续到应用程序崩溃。这似乎发生在datastructureFromManagedObject方法中的递归中。我怀疑这种方法：

1） 查看第一个托管对象并递归遵循任何关系属性。 2） 检查在第1点找到的关系的另一端的对象，并重复该过程

如果管理的对象A与对象B存在一对多关系，并且这种关系是双向的（即从B到A的关系是反向的-例如，一个部门有许多员工，但每个员工只有一个部门）下面的代码陷入无限递归，因为它遵循从对象B到对象A的一对一关系，依此类推

如果是这样的话，有谁能提供一个解决方案，这样我就可以将托管对象的整个对象图转换为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

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当你在原始帖子上发表评论时，我回答了这个问题。您需要对递归的工作方式进行一些更改，以便它不会进入循环。有很多方法可以做到这一点

例如，您可以更改调用以获取所有关系，改为在

NSManagedObject

子类中调用仅返回下游关系的方法。在该设计中，ObjectA将返回ObjectB关系，但ObjectB不会返回任何关系（或与ObjectC的关系，等等）。这将为递归创建一个树状层次结构

遵循代码的逻辑。它处理您交给它的一个或多个对象，然后遍历与第一组对象关联的每个对象。从你的帖子中，你已经表明你明白这是一个循环。现在，您需要在代码中用逻辑中断该循环，以将其从循环更改为树

此外，我意识到这听起来像是在给我的书拉皮条，我在书中关于导出食谱的多线程章节中解释了如何避免这种循环

更新NSDate

---

这听起来像是您正在使用的JSON解析器中的一个bug，因为它应该能够处理日期。但是，您的解决方案是可行的，除非您需要在PITA的两侧进行转换。我会查看您的解析器，看看它为什么不能正确地翻译日期，因为这是一个相当大的遗漏

我只想指出一个小的输入错误，它导致了代码崩溃，希望这能节省您几分钟的时间

- (NSArray*)dataStructuresFromManagedObjects:(NSArray*)managedObjects {

    NSMutableArray *dataArray = [[NSArray alloc] init];
    for (NSManagedObject *managedObject in managedObjects) {
        [dataArray addObject:[self dataStructureFromManagedObject:managedObject]];
    }
    return [dataArray autorelease];
}

NSMutableArray*dataArray=[[NSArray alloc]init]；//这应该是NSMutableArray

实际上应该是NSMutableArray*dataArray=[[NSMutableArray alloc]init]

仅此而已

---

谢谢你

谢谢你的回复。我想我已经设法解决了无休止的递归问题，但代码现在抛出了一个异常，似乎表明NSDate属性无法序列化（即，由于未捕获的异常“NSGenericeException”终止应用程序，原因：“cannot serialized data of type”\uu NSCFDate“”）是这样吗？如果是的话，有什么办法可以解决这个问题吗？我已经买了你的书，并将努力读得更详细。再次感谢你迄今为止的帮助。我是Objective-C初学者，正在尝试在这方面取得一些进展。通过将[date-timeIntervalSince1970]返回的值存储为NSNumber，我解决了上述问题。我会看看你在书中提到的部分。