Restkit mapping structure that worked for me (not using core data)

ILAppDelegate.m

//
//  ILAppDelegate.m
//
//  Created by Adrian Gzz on 25/09/13.
//

...
#import "ILMappingManager.h"
...

@implementation ILAppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  ...
  [ILMappingManager setup];
  ...
}

ILMappingManager.h

//
//  ILMappingManager.h
//
//  Created by Adrian Gonzalez on 9/18/13.
//

#import <Foundation/Foundation.h>
#import <RestKit/RestKit.h>
typedef void (^ RKSuccessBlock)(RKObjectRequestOperation *operation, RKMappingResult *mappingResult);
typedef void (^ RKFailureBlock)(RKObjectRequestOperation *operation, NSError *error);

@interface ILMappingManager : NSObject

+ (void)setup;
+ (NSIndexSet *)statusCodeSet;

@end

@protocol ILMapper <NSObject>

+ (RKObjectMapping *)mapping;
+ (RKObjectMapping *)mappingWithRelationships;
+ (NSArray *)responseDescriptors;
+ (NSArray *)requestDescriptors;
+ (void)addRelationships;

@end

ILMappingManager.m

//
//  ILMappingManager.m
//
//  Created by Adrian Gonzalez on 9/18/13.
//

#import "ILMappingManager.h"
#import "ILApiClient.h"
// all model mappings
#import "ILModelExampleMapping.h"
// ---
#import <RestKit/RestKit.h>

@implementation ILMappingManager

+ (void)setup
{
    RKObjectManager *manager = [[RKObjectManager alloc] initWithHTTPClient:[ILApiClient sharedClient]];
    [RKObjectManager setSharedManager:manager];
    
    NSArray *mappingClasses = @[[ILModelExampleMapping class], all model maping classes...];
    
    // preload mappings
    [self preloadMappings:mappingClasses];
    
    // preload relationships
    [self preloadRelatioships:mappingClasses];
    
    //Response Descriptors
    [self addResponseDescriptorsForMappings:mappingClasses];
    
    //Request Descriptors
    [self addRequestDescriptorsForMappings:mappingClasses];
    
    //Pagination
    [self addPaginationMapping];
    
}

+ (NSIndexSet *)statusCodeSet {
    return RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful);
}

+ (void)addResponseDescriptorsForMappings:(NSArray *)mappingClasses {
    for (id<ILMapper> mappingClass in mappingClasses) {
        [[RKObjectManager sharedManager] addResponseDescriptorsFromArray:[mappingClass responseDescriptors]];
    }
}

+ (void)addRequestDescriptorsForMappings:(NSArray *)mappingClasses {
    for (id<ILMapper> mappingClass in mappingClasses) {
        [[RKObjectManager sharedManager] addRequestDescriptorsFromArray:[mappingClass requestDescriptors]];
    }
}

+ (void)addPaginationMapping
{
    RKObjectMapping *paginationMapping = [RKObjectMapping mappingForClass:[RKPaginator class]];
    RKObjectManager *objectManager = [RKObjectManager sharedManager];
    
    [paginationMapping addAttributeMappingsFromDictionary:@{
                                                            @"meta.pagination.per_page":@"perPage",
                                                            @"meta.pagination.total_pages":@"pageCount",
                                                            @"meta.pagination.total_objects":@"objectCount"
                                                            }];
    
    [objectManager setPaginationMapping:paginationMapping];
}

+(void)preloadMappings:(NSArray *)mappingClasses
{
    for (id<ILMapper> mappingClass in mappingClasses) {
        [mappingClass mapping];
    }
}

+(void)preloadRelatioships:(NSArray *)mappingClasses
{
    for (id<ILMapper> mappingClass in mappingClasses) {
        [mappingClass addRelationships];
    }
}

@end

ILModelMappingExample.h

//
//  ILModelMappingExample.h
//
//  Created by Adrian Gzz on 17/10/13.
//

#import <Foundation/Foundation.h>
#import <RestKit/RestKit.h>
#import "ILMappingManager.h"

@interface ILModelMappingExample : NSObject <ILMapper>

+ (NSArray *) responseDescriptors;
+ (NSArray *) requestDescriptors;
+ (RKObjectMapping *) mapping;
+ (RKObjectMapping *)mappingWithRelationships;
+ (void)addRelationships;

@end

ILModelMappingExample.m

//
//  ILModelMappingExample.m
//
//  Created by Adrian Gonzalez on 9/18/13.
//

#import "ILModelMappingExample.h"
#import "ILModelExample.h"
#import "ILMappingManager.h"
#import <RestKit/RestKit.h>

@implementation ILModelMappingExample

+ (RKObjectMapping *)mapping
{
    static RKObjectMapping *_mapping = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        RKObjectMapping *mapping = [RKObjectMapping mappingForClass:[ILModelExample class]];
        [mapping addAttributeMappingsFromArray:@[@"name", @"email", ...]];
        [mapping addAttributeMappingsFromDictionary:@{
                                                      @"id": @"userId",
                                                      ...
                                                    }];
 
        _mapping = mapping;
    });
    return _mapping;
}

+(RKObjectMapping *)mappingWithRelationships
{
    static RKObjectMapping *_mapping = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _mapping = [[self mapping] copy];
    });
    return _mapping;
}

+(void)addRelationships
{
    RKObjectMapping *mapping = [self mappingWithRelationships];
    [mapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"friends"
                                                                            toKeyPath:@"friends"
                                                                          withMapping:[ILModelMappingExample mappingWithRelationships]]];
}

+ (NSArray *)responseDescriptors
{
    RKResponseDescriptor *showDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:[self mappingWithRelationships]
                                                                                         method:RKRequestMethodGET
                                                                                    pathPattern:@"model_example/:id"
                                                                                        keyPath:@"model_example"
                                                                                    statusCodes:[ILModelMappingExample statusCodeSet]];
    RKResponseDescriptor *otherDescriptor = ...
    
    return @[showDescriptor, otherDescriptor, ...];
    
}

+ (NSArray *)requestDescriptors
{
    RKRequestDescriptor *createDescriptor = [RKRequestDescriptor requestDescriptorWithMapping:[[self mapping] inverseMapping]
                                                                                  objectClass:[ILModelExample class]
                                                                                  rootKeyPath:@"model_example"
                                                                                       method:RKRequestMethodAny];
    RKRequestDescriptor *otherDescriptor = ... 
    
    return @[createDescriptor, otherDescriptor, ...];
}

@end