JSON和核心数据在iPhone上
我有一个核心数据对象图（由两个实体链接到一对多的关系）。
我很好奇，作为一个相对缺乏经验的iPhone开发人员，是否有人可以推荐一种方法，并为iPhone合适的JSON实现，这将允许我：
1）将核心数据logging转换成JSONstring（同时保持实体之间的关系）; 和
2）将JSONstring转换回核心数据对象（再次保留实体之间的关系）。
我已经search了一个关于这一点的教程/代码示例，但是没有成功，所以我会很感激地收到任何帮助。
首先，select一个JSON库来使用，我个人喜欢TouchJSON，但其他几个也相当不错。 复杂的部分虽然不是非常困难，但是可以将您的托pipe对象转换为合适的转换结构。 我写这个真快，所以它可能有一个错误或两个:)
你调用的方法是：
- (NSString*)jsonStructureFromManagedObjects:(NSArray*)managedObjects; - (NSArray*)managedObjectsFromJSONStructure:(NSString*)json withManagedObjectContext:(NSManagedObjectContext*)moc;
实施情况如下：
- (NSDictionary*)dataStructureFromManagedObject:(NSManagedObject*)managedObject { NSDictionary *attributesByName = [[managedObject entity] attributesByName]; NSDictionary *relationshipsByName = [[managedObject entity] relationshipsByName]; NSMutableDictionary *valuesDictionary = [[managedObject dictionaryWithValuesForKeys:[attributesByName allKeys]] mutableCopy]; [valuesDictionary setObject:[[managedObject entity] name] forKey:@"ManagedObjectName"]; for (NSString *relationshipName in [relationshipsByName allKeys]) { NSRelationshipDescription *description = [[[managedObject entity] relationshipsByName] objectForKey:relationshipName]; if (![description isToMany]) { NSManagedObject *relationshipObject = [managedObject valueForKey:relationshipName]; [valuesDictionary setObject:[self dataStructureForManagedObject:relationshipObject] forKey:relationshipName]; continue; } NSSet *relationshipObjects = [managedObject objectForKey:relationshipName]; NSMutableArray *relationshipArray = [[NSMutableArray alloc] init]; for (NSManagedObject *relationshipObject in relationshipObjects) { [relationshipArray addObject:[self dataStructureForManagedObject:relationshipObject]]; } [valuesDictionary setObject:relationshipArray forKey:relationshipName]; } return [valuesDictionary autorelease]; } - (NSArray*)dataStructuresFromManagedObjects:(NSArray*)managedObjects { NSMutableArray *dataArray = [[NSMutableArray alloc] init]; for (NSManagedObject *managedObject in managedObjects) { [dataArray addObject:[self dataStructureForManagedObject:managedObject]]; } return [dataArray autorelease]; } - (NSString*)jsonStructureFromManagedObjects:(NSArray*)managedObjects { NSArray *objectsArray = [self dataStructuresFromManagedObjects:managedObjects]; 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 = [relationshipsByName objectForKey:relationshipName]; if (![description isToMany]) { NSDictionary *childStructureDictionary = [structureDictionary objectForKey:relationshipName]; NSManagedObject *childObject = [self managedObjectFromStructure:childStructureDictionary withManagedObjectContext:moc]; [managedObject setObject:childObject forKey:relationshipName]; continue; } NSMutableSet *relationshipSet = [managedObject mutableSetForKey:relationshipName]; NSArray *relationshipArray = [structureDictionary objectForKey:relationshipName]; for (NSDictionary *childStructureDictionary in relationshipArray) { NSManagedObject *childObject = [self managedObjectFromStructure:childStructureDictionary withManagedObjectContext:moc]; [relationshipSet addObject:childObject]; } } return managedObject; } - (NSArray*)managedObjectsFromJSONStructure:(NSString*)json withManagedObjectContext:(NSManagedObjectContext*)moc { NSError *error = nil; NSArray *structureArray = [[CJSONDeserializer deserializer] deserializeAsArray:json 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]; }
现在这是recursion的，所以如果你不小心，你可以很容易地翻译你的整个持久存储。 注意你的关系，并确保它们只是“向下”对象树，这样你才能得到你想要翻译的对象。
我只是想指出一个小小的错字，导致代码崩溃，希望这会为您节省几分钟的时间。
- (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]; // This should be NSMutableArray NSMutableArray *dataArray = [[NSArray alloc] init]; // This should be NSMutableArray
真的应该是NSMutableArray *dataArray = [[NSMutableArray alloc] init];
就这些。
谢谢
使用Rails同步核心数据是一个详细的演示文稿，其中包括用于从JSON序列化/反序列化Core Data对象的示例代码（跳到核心数据部分的幻灯片55）。 他的示例代码假设一个相当简单的模型没有关系，但我认为这将是很容易扩展。
该演示文稿还详细介绍了如何使您的Core Data模型与基于REST的Web应用程序保持同步，并指向一些有用的库（包括ObjectiveResource和ASIHTTPRequest） 。 不知道这是你想要做什么，但值得一看，即使是核心数据代码。
如果您的托pipe对象中有一个NSDate ，如上面其中一个注释中所提到的，则序列化包含NSDate的对象时会遇到问题。 一个简单的解决方法是使用objective-c类别向NSDate添加JSONDataRepresentation方法。
将这两个文件添加到您的项目中：
NSdate.h：
#import <Foundation/Foundation.h> @interface NSDate (jsondatarepresentation) - (NSData*) JSONDataRepresentation; @end
NSDate.m：
#import "NSDate.h" @implementation NSDate (jsondatarepresentation) - (NSData*) JSONDataRepresentation { return [[[NSNumber numberWithDouble:[self timeIntervalSince1970]] stringValue] dataUsingEncoding:NSUTF8StringEncoding]; } @end
有一个lib为你做JSON同步： https ： //github.com/sixdegrees/lidenbrock
我遇到这个post，工作得很好。
http://touchalicious.com/blog/2009/10/25/turn-core-data-models-into-json.html
由于这是recursion的，所以多对多的关系将会自行循环。 为了避免这种情况，我在Core Data模型中的关系的用户信息字典中添加了一个“isExportable”键。 然后你可以检查这个键，并select不循环没有它的关系。
if ([property isKindOfClass:[NSRelationshipDescription class]]) { NSRelationshipDescription *relationshipDescription = (NSRelationshipDescription *)property; if ([[[relationshipDescription userInfo] objectForKey:@"isExportable"] boolValue] == YES) { NSString *name = [relationshipDescription name]; if ([relationshipDescription isToMany]) { NSMutableArray *arr = [properties valueForKey:name]; if (!arr) { arr = [[NSMutableArray alloc] init]; [properties setValue:arr forKey:name]; } for (NSManagedObject *o in [self mutableSetValueForKey:name]) { [arr addObject:[o propertiesDictionary]]; } } else { NSManagedObject *o = [self valueForKey:name]; [properties setValue:[o propertiesDictionary] forKey:name]; } } } }
只是以为ID发布了这个问题的快速更新。 我遵循Marcus和Brandon的解答，为JSON导出提出了这个问题（它仍然使用TouchJSON）：
- (NSData*)jsonStructureFromManagedObjects:(NSArray*)managedObjects { NSArray *objectsArray = [self dataStructuresFromManagedObjects:managedObjects]; NSData *jsonData = [[CJSONSerializer serializer] serializeArray:objectsArray error:nil]; return jsonData; } - (NSArray*)dataStructuresFromManagedObjects:(NSArray*)managedObjects { NSMutableArray *dataArray = [[NSMutableArray alloc] init]; for (NSManagedObject *managedObject in managedObjects) { [dataArray addObject:[self dataStructureFromManagedObject:managedObject]]; } return dataArray; } - (NSDictionary*)dataStructureFromManagedObject:(NSManagedObject*)managedObject { NSDictionary *attributesByName = [[managedObject entity] attributesByName]; NSDictionary *relationshipsByName = [[managedObject entity] relationshipsByName]; NSMutableDictionary *valuesDictionary = [[managedObject dictionaryWithValuesForKeys:[attributesByName allKeys]] mutableCopy]; [valuesDictionary setObject:[[managedObject entity] name] forKey:@"ManagedObjectName"]; for (NSString *relationshipName in [relationshipsByName allKeys]) { NSRelationshipDescription *description = [[[managedObject entity] relationshipsByName] objectForKey:relationshipName]; if ([[[description userInfo] objectForKey:@"isExportable"] boolValue] == YES) { if (![description isToMany]) { NSManagedObject *relationshipObject = [managedObject valueForKey:relationshipName]; if (relationshipObject) { [valuesDictionary setObject:[self dataStructureFromManagedObject:relationshipObject] 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; }
我无法得到导入工作，也许这与事实我正在使用魔法logging我不知道，所以我只是循环传入的JSONstream和手动创build对象…
Marcus S. Zarra激发了我将recursion的想法带到了一个工作版本。 在这个版本中，你不需要在CoreData中设置一个键，你可以剪切并粘贴到你的项目中:-)
// MARK: - encoding and decoding CoreData entity to dictionary func dataStructureFromManagedObject( managedObject:NSManagedObject?, parentEntity: NSEntityDescription? = nil) -> NSMutableDictionary { if (managedObject != nil) { var attributesByName: NSDictionary = managedObject!.entity.attributesByName var relationshipsByName: NSDictionary = managedObject!.entity.relationshipsByName var valuesImmutableDictionary: NSDictionary = managedObject!.dictionaryWithValuesForKeys( attributesByName.allKeys) var valuesDictionary: NSMutableDictionary = valuesImmutableDictionary.mutableCopy() as NSMutableDictionary valuesDictionary.setObject( managedObject!.entity.name!, forKey: "ManagedObjectName") for relationshipNameObject in relationshipsByName.allKeys { var relationshipName: NSString = relationshipNameObject as NSString var relationshipDescription: NSRelationshipDescription? = relationshipsByName.objectForKey( relationshipName) as? NSRelationshipDescription if !relationshipDescription!.toMany { // ono to one if parentEntity == nil || (relationshipDescription! as NSRelationshipDescription).destinationEntity != parentEntity! { // no parent or relationship is "downward" -> object for relationship must be added var relationshipObject: NSManagedObject? = managedObject!.valueForKey( relationshipName) as? NSManagedObject var relationshipObjectDictionary: NSMutableDictionary = self.dataStructureFromManagedObject( relationshipObject, parentEntity: managedObject?.entity) valuesDictionary.setObject( relationshipObjectDictionary, forKey: relationshipName) } else { // relationship is "upward" -> nothing to do } } else { // one to many -> all objects must be added var relationshipObjects: NSSet = managedObject!.mutableSetValueForKey( relationshipName) var relationshipArray:NSMutableArray = [] for relationshipObjectRaw in relationshipObjects { var relationshipObject:NSManagedObject? = relationshipObjectRaw as? NSManagedObject if relationshipObject != nil && !relationshipObject!.entity.isKindOfEntity( managedObject!.entity) { relationshipArray.addObject(self.dataStructureFromManagedObject( relationshipObject, parentEntity: managedObject?.entity)) } } valuesDictionary.setObject( relationshipArray, forKey: relationshipName) } } return valuesDictionary } else { return NSMutableDictionary() } } func managedObjectFromStructure( structureDictionary: NSDictionary, moc: NSManagedObjectContext, parentObject: NSManagedObject? = nil) -> NSManagedObject { if structureDictionary.count > 0 { var objectName:NSString = structureDictionary.objectForKey( "ManagedObjectName") as NSString var managedObject:NSManagedObject = NSEntityDescription.insertNewObjectForEntityForName( objectName, inManagedObjectContext: moc) as NSManagedObject var relationshipsByName: NSDictionary = managedObject.entity.relationshipsByName var realObjectStructure:NSMutableDictionary = structureDictionary.mutableCopy() as NSMutableDictionary realObjectStructure.removeObjectForKey( "ManagedObjectName") for key in realObjectStructure.allKeys { // search for "ManagedObjectName" relationship entrys and delete them before filling the managedObject from this structure for relationshipName in relationshipsByName.allKeys { if relationshipName as NSString == key as NSString { realObjectStructure.removeObjectForKey( key) } } } managedObject.setValuesForKeysWithDictionary( realObjectStructure) // the main object with attributes is created. Now care about the relationships for relationshipName in managedObject.entity.relationshipsByName.keys { var description:NSRelationshipDescription = relationshipsByName.objectForKey( relationshipName) as NSRelationshipDescription if !description.toMany { // to one relationship if parentObject == nil || description.destinationEntity != parentObject!.entity { // no parent or relationship is "downward" -> recurse structure to add var childStructureDictionary:NSDictionary = structureDictionary.objectForKey( relationshipName) as NSDictionary if childStructureDictionary.count > 0 { // dictionary not empty -> object must be created and added var childObject:NSManagedObject? = self.managedObjectFromStructure( childStructureDictionary, moc: moc, parentObject: managedObject) // validateForUpdate var error:NSError? if !managedObject.validateForUpdate( &error) { println("Error: Object not in valid state for update!!! -> \(error)") } else { managedObject.setValue( childObject, forKey: relationshipName as NSString) } } else { // relationship is "upward" -> nothing to do } } } else { // to many relationship var relationshipSet:NSMutableSet = managedObject.mutableSetValueForKey( relationshipName as NSString) var relationshipArray:NSArray = structureDictionary.objectForKey( relationshipName as NSString) as NSArray for childStructureDictionary in relationshipArray { if childStructureDictionary.count > 0 { // dictionary not empty -> object must be created and added var childObject:NSManagedObject = self.managedObjectFromStructure( childStructureDictionary as NSDictionary, moc: moc, parentObject: managedObject) // validateForUpdate var error:NSError? if !managedObject.validateForUpdate( &error) { println( "Error: Object not in valid state for update!!! -> \(error)") } else { relationshipSet.addObject( childObject) } } else { // no object was behind the relationship -> nothing to do } } // save set managedObject.setValue( relationshipSet, forKey: relationshipName as NSString) } } // final check validateForUpdate var error:NSError? if !managedObject.validateForUpdate( &error) { println( "Error: Object not in valid state for update although all previous check are passed!!! -> \(error)") } return managedObject } else { println( "Error: structure for object was empty. this should not happen at this point") var objectName:NSString = structureDictionary.objectForKey( "ManagedObjectName") as NSString var managedObject:NSManagedObject = NSEntityDescription.insertNewObjectForEntityForName( objectName, inManagedObjectContext: moc) as NSManagedObject return managedObject } } func dataStructuresFromManagedObjects( managedObjects: NSArray) -> NSArray { var dataArray:NSMutableArray = [] for managedObject in managedObjects { dataArray.addObject( self.dataStructureFromManagedObject(managedObject as? NSManagedObject)) } return dataArray }
这里的关键是将父实体作为parameter passing给recursion，所以我们可以决定我们必须填充数据的关系。 因此，这两个函数： dataStructureFromManagedObject和managedObjectFromStructure可以将任何实体对象从CoreData编码和解码成一个字典，并回到一个对象。
