Deserializing local NSString of JSON into objects via RestKit (no network download)

Question

Is it possible to deserialize an NSString of JSON into objects via RestKit? I checked the API list here and could not find something that would serve for this purpose. The closest I could find are the various parser classes that return NSDictionary after parsing the input. I assume RestKit uses these parsers after downloading the response so my thinking is that the functionality is available somewhere in RestKit but not exposed publicly.

If I am not missing anything and this functionality is not exposed, what would be the alternatives? Two obvious ones do not look very promising: Get the resulting NSDictionary and try to deserialize myself (effectively reimplementing RestKit) or try to dive into RestKit source and see if this can be somehow exposed (looks tedious and error prone).

Thanks in advance for any help.

PS: The idea is that a string property on a deserialized object is actually the JSON representation of another set of objects (embedded JSON in a sense) and it is deserialized on demand during runtime.

Answer 1

Pretty "simple":

NSString *stringJSON;
...

RKJSONParserJSONKit *parser;
NSError *error= nil;
parser= [[[RKJSONParserJSONKit alloc] init] autorelease]; 
MyManagedObject *target;
target= [MyManagedObject object];

NSDictionary *objectAsDictionary;
RKObjectMapper* mapper;
objectAsDictionary= [parser objectFromString:stringJSON error:&error];
mapper = [RKObjectMapper mapperWithObject:objectAsDictionary 
                          mappingProvider:[RKObjectManager sharedManager].mappingProvider];
mapper.targetObject = target;
RKObjectMappingResult* result = [mapper performMapping];
NSLog(@"%@", [result asObject]);

Answer 2

As of RestKit 0.20.0-pre2

NSString* JSONString = @"{ \"name\": \"The name\", \"number\": 12345}";
NSString* MIMEType = @"application/json";
NSError* error;
NSData *data = [JSONString dataUsingEncoding:NSUTF8StringEncoding];
id parsedData = [RKMIMETypeSerialization objectFromData:data MIMEType:MIMEType error:&error];
if (parsedData == nil && error) {
    // Parser error...
}

AppUser *appUser = [[AppUser alloc] init];

NSDictionary *mappingsDictionary = @{ @"someKeyPath": someMapping };
RKMapperOperation *mapper = [[RKMapperOperation alloc] initWithRepresentation:parsedData mappingsDictionary:mappingsDictionary];
mapper.targetObject = appUser;
NSError *mappingError = nil;
BOOL isMapped = [mapper execute:&mappingError];
if (isMapped && !mappingError) {
    // Yay! Mapping finished successfully
    NSLog(@"mapper: %@", [mapper representation]);
    NSLog(@"firstname is %@", appUser.firstName);
}

Answer 3

This works for Restkit 0.21.0:

NSString* jsonFilePath = [[NSBundle mainBundle] pathForResource:@"fileName"
                                                 ofType:@"json"];

NSString* JSONString = [NSString stringWithContentsOfFile:jsonFilePath
                                              encoding:NSUTF8StringEncoding
                                                 error:NULL];


NSError* error;
NSData *data = [JSONString dataUsingEncoding:NSUTF8StringEncoding];
id parsedData = [RKMIMETypeSerialization objectFromData:data MIMEType:RKMIMETypeJSON error:&error];
if (parsedData == nil && error) {
    // Parser error...
}

//_objectManager is RKObjectManager instance
NSMutableDictionary *mappingsDictionary = [[NSMutableDictionary alloc] init];
for (RKResponseDescriptor *descriptor in _objectManager.responseDescriptors) {
    [mappingsDictionary setObject:descriptor.mapping forKey:descriptor.keyPath];
}

RKMapperOperation *mapper = [[RKMapperOperation alloc] initWithRepresentation:parsedData mappingsDictionary:mappingsDictionary];
NSError *mappingError = nil;
BOOL isMapped = [mapper execute:&mappingError];
if (isMapped && !mappingError) {
    NSLog(@"result %@",[mapper mappingResult]);
}