Objective C + RESTKit: Problems with getting Objects

Question

I want to use RestKit for a Restful Webservice to communicate between an LAMP-environment and an iOS-App. Therefore I made a first test to check out if it all works out like described in the tutorials available and on the RestKit page.

Right now the code looks like this:

RKObjectManager* objectManager = [RKObjectManager managerWithBaseURLString:@"http://localhost/resttest"];

objectManager.client.requestQueue.showsNetworkActivityIndicatorWhenBusy = YES;

#ifdef RESTKIT_GENERATE_SEED_DB
    NSString *seedDatabaseName = nil;
    NSString *databaseName = RKDefaultSeedDatabaseFileName;
#else
    NSString *seedDatabaseName = RKDefaultSeedDatabaseFileName;
    NSString *databaseName = @"CoreData.sqlite";
#endif

objectManager.objectStore = [RKManagedObjectStore objectStoreWithStoreFilename:databaseName usingSeedDatabaseName:seedDatabaseName managedObjectModel:nil delegate:self];

// Map Person Object
RKManagedObjectMapping *personMapping = [RKManagedObjectMapping mappingForClass:[Person class] inManagedObjectStore:objectManager.objectStore];
//RKManagedObjectMapping *personMapping = [RKManagedObjectMapping mappingForEntityWithName:@"Person" inManagedObjectStore:[RKObjectManager sharedManager].objectStore];
[personMapping mapKeyPath:@"id" toAttribute:@"person_id"];
[personMapping mapKeyPath:@"firstname" toAttribute:@"person_firstname"];
[personMapping mapKeyPath:@"lastname" toAttribute:@"person_lastname"];
[personMapping mapKeyPath:@"gender" toAttribute:@"person_gender"];
personMapping.primaryKeyAttribute = @"id";


// Register our mappings with the provider;    
[objectManager.mappingProvider setMapping:personMapping forKeyPath:@"/person"];
objectManager.acceptMIMEType = RKMIMETypeJSON;

#ifdef RESTKIT_GENERATE_SEED_DB
    RKLogConfigureByName("RestKit/ObjectMapping", RKLogLevelInfo);
    RKLogConfigureByName("RestKit/CoreData", RKLogLevelTrace);
#endif

[objectManager loadObjectsAtResourcePath:@"/person" delegate:self];

This is how my Managed Object looks like:

@interface Person : NSManagedObject

@property (nonatomic, retain) NSString * person_firstname;
@property (nonatomic, retain) NSString * person_lastname;
@property (nonatomic, retain) NSString * person_gender;
@property (nonatomic, retain) NSNumber * person_id;

@end

And this is the dummy-code on server side which only returns some json example string:

<?php

    header('Content-type: application/json');

    if($_SERVER['REQUEST_METHOD'] == 'GET')
    {
        $json_string = '{ "persons": [
                            { "id": "1",
                              "firstname": "hans",
                              "lastname": "maier",
                              "genre": "m"
                            },
                            { "id": "2",
                              "firstname": "michael",
                              "lastname": "schmidt",
                              "genre": "w"
                            }]
                        }';

        echo $json_string;
    }

?>

The URI to get the returned json-String is http://localhost/resttest/person(/index.php).

My problems are:

• I always get this Error when i don't define a resource path for '':

  E restkit.network:RKObjectLoader.m:216 Encountered errors during mapping: Could not find an object mapping for keyPath: ''

and I don't know why this happens. No other example I tried has this problem, but I don't have a clue what I'm doing wrong.

• When it works (I have to change the Base URL to http://localhost/resttest/person), I get an empty object instead of an error.

I would appreciate any help on this topic, because right now i don't know what I'm doing wrong.

Thank you!

Edit 03.05.2012:

Here is what i get in the logs:

2012-05-03 12:52:05.067 RESTKitCoreDataTest[5139:13807] D restkit.object_mapping:RKObjectMapper.m:320 Performing object mapping sourceObject: {
    persons =     (
                {
            firstname = hans;
            gender = m;
            id = 1;
            lastname = maier;
        },
                {
            firstname = michael;
            gender = w;
            id = 2;
            lastname = schmidt;
        }
    );
}
 and targetObject: (null)
2012-05-03 12:52:05.067 RESTKitCoreDataTest[5139:13807] T restkit.object_mapping:RKObjectMapper.m:278 Examining keyPath '' for mappable content...
2012-05-03 12:52:05.067 RESTKitCoreDataTest[5139:13807] D restkit.object_mapping:RKObjectMapper.m:264 Found mappable data at keyPath '': {
    persons =     (
                {
            firstname = hans;
            gender = m;
            id = 1;
            lastname = maier;
        },
                {
            firstname = michael;
            gender = w;
            id = 2;
            lastname = schmidt;
        }
    );
}
2012-05-03 12:52:05.073 RESTKitCoreDataTest[5139:13807] D restkit.object_mapping:RKObjectMapper.m:210 Asked to map source object {
    persons =     (
                {
            firstname = hans;
            gender = m;
            id = 1;
            lastname = maier;
        },
                {
            firstname = michael;
            gender = w;
            id = 2;
            lastname = schmidt;
        }
    );
} with mapping <RKManagedObjectMapping:0x811eb60 objectClass=Person keyPath mappings => (
    "RKObjectKeyPathMapping: id => person_id",
    "RKObjectKeyPathMapping: firstname => person_firstname",
    "RKObjectKeyPathMapping: lastname => person_lastname",
    "RKObjectKeyPathMapping: gender => person_gender"
)>
2012-05-03 12:52:05.074 RESTKitCoreDataTest[5139:13807] D restkit.object_mapping:RKObjectMappingOperation.m:617 Starting mapping operation...
2012-05-03 12:52:05.074 RESTKitCoreDataTest[5139:13807] T restkit.object_mapping:RKObjectMappingOperation.m:618 Performing mapping operation: RKObjectMappingOperation for 'Person' object. Mapping values from object {
    persons =     (
                {
            firstname = hans;
            gender = m;
            id = 1;
            lastname = maier;
        },
                {
            firstname = michael;
            gender = w;
            id = 2;
            lastname = schmidt;
        }
    );
} to object <Person: 0x6e295d0> (entity: Person; id: 0x6e29610 <x-coredata:///Person/t99EFF6DC-EBDA-405C-8AFF-D082E4A8542F2> ; data: {
    "person_firstname" = nil;
    "person_gender" = nil;
    "person_id" = 0;
    "person_lastname" = nil;
}) with object mapping <RKManagedObjectMapping:0x811eb60 objectClass=Person keyPath mappings => (
    "RKObjectKeyPathMapping: id => person_id",
    "RKObjectKeyPathMapping: firstname => person_firstname",
    "RKObjectKeyPathMapping: lastname => person_lastname",
    "RKObjectKeyPathMapping: gender => person_gender"
)>
2012-05-03 12:52:05.074 RESTKitCoreDataTest[5139:13807] T restkit.object_mapping:RKObjectMappingOperation.m:388 Did not find mappable attribute value keyPath 'id'
2012-05-03 12:52:05.074 RESTKitCoreDataTest[5139:13807] T restkit.object_mapping:RKObjectMappingOperation.m:388 Did not find mappable attribute value keyPath 'firstname'
2012-05-03 12:52:05.075 RESTKitCoreDataTest[5139:13807] T restkit.object_mapping:RKObjectMappingOperation.m:388 Did not find mappable attribute value keyPath 'lastname'
2012-05-03 12:52:05.075 RESTKitCoreDataTest[5139:13807] T restkit.object_mapping:RKObjectMappingOperation.m:388 Did not find mappable attribute value keyPath 'gender'
2012-05-03 12:52:05.075 RESTKitCoreDataTest[5139:13807] D restkit.object_mapping:RKObjectMappingOperation.m:638 Mapping operation did not find any mappable content
2012-05-03 12:52:05.075 RESTKitCoreDataTest[5139:13807] T restkit.core_data:RKManagedObjectMappingOperation.m:98 relationshipsAndPrimaryKeyAttributes: {
}
2012-05-03 12:52:05.075 RESTKitCoreDataTest[5139:13807] D restkit.object_mapping:RKObjectMapper.m:351 The following operations are in the queue: (
)
2012-05-03 12:52:05.075 RESTKitCoreDataTest[5139:13807] D restkit.object_mapping:RKObjectMapper.m:366 Finished performing object mapping. Results: {
}
2012-05-03 12:52:05.080 RESTKitCoreDataTest[5139:fb03] Loaded persons: (
)

Answer 1

Possibility 1:

It seems that your setting the mapping to the wrong keypath.

Try

// Register our mappings with the provider;    
[objectManager.mappingProvider setMapping:personMapping forKeyPath:@"persons"];

and check if it works.

Possibility 2:

Specify the root path of your JSON in your mapping.

Try

// Map Person Object
RKManagedObjectMapping *personMapping = [RKManagedObjectMapping mappingForClass:[Person class] inManagedObjectStore:objectManager.objectStore];
[personMapping mapKeyPath:@"id" toAttribute:@"person_id"];
[personMapping mapKeyPath:@"firstname" toAttribute:@"person_firstname"];
[personMapping mapKeyPath:@"lastname" toAttribute:@"person_lastname"];
[personMapping mapKeyPath:@"gender" toAttribute:@"person_gender"];
personMapping.rootKeyPath = @"persons";
personMapping.primaryKeyAttribute = @"id";

and check if it works.