AFIncrementalStore with If-Modified-Since hack

AppDelegate.m

// Connecting AFIncrementalStore & MagicRecord

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { 

    PDDebugger *debugger = [PDDebugger defaultInstance];
    [debugger connectToURL:[NSURL URLWithString:@"ws://localhost:9000/device"]];
    [debugger enableNetworkTrafficDebugging];
    [debugger forwardAllNetworkTraffic];
    [debugger enableCoreDataDebugging];
    
    [self setupCoreDataStack];

    // Bla boa
    [self.window makeKeyAndVisible];
    return YES;
}

- (void)setupCoreDataStack {
    //[MagicalRecord setupCoreDataStackWithStoreNamed:@"Events.sqlite"];
    
    NSManagedObjectModel *model = [NSManagedObjectModel MR_defaultManagedObjectModel];
    NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:model];
    
    AFIncrementalStore *incrementalStore = (AFIncrementalStore *)[psc addPersistentStoreWithType:[EventsIncrementalStore type] configuration:nil URL:nil options:nil error:nil];
    
    NSDictionary *options = @{
        NSInferMappingModelAutomaticallyOption : @(YES),
        NSMigratePersistentStoresAutomaticallyOption: @(YES)
    };
    
    [incrementalStore.backingPersistentStoreCoordinator MR_addSqliteStoreNamed:@"Events.sqlite" withOptions:options];
    
    [NSPersistentStore setDefaultPersistentStore:incrementalStore];
    [NSPersistentStoreCoordinator MR_setDefaultStoreCoordinator:incrementalStore.persistentStoreCoordinator];
    [NSManagedObjectContext MR_initializeDefaultContextWithCoordinator:incrementalStore.persistentStoreCoordinator];

    // Totally needed to reset MR-MOCs after AFIS 
    [[NSNotificationCenter defaultCenter] addObserverForName:NSManagedObjectContextDidSaveNotification
                                                      object:nil
                                                       queue:[NSOperationQueue mainQueue]
                                                  usingBlock:^(NSNotification *note) {
                                                      NSManagedObjectContext *moc0 = [note object];
                                                      NSManagedObjectContext *moc = [NSManagedObjectContext MR_rootSavingContext];
                                                      NSManagedObjectContext *moc2 = [NSManagedObjectContext MR_defaultContext];
                                                      
                                                      
                                                      if ((![moc0 isEqual:moc]) && (![moc0 isEqual:moc2]) && [moc0 persistentStoreCoordinator] == [moc persistentStoreCoordinator]) {
                                                          [moc reset];
                                                          [moc2 reset];
                                                      }
                                                  }];
}

EventsAPIClient.m

//
//  EventsAPIClient.m
//
//  Created by Taras Kalapun on 10/8/12.
//

#import "EventsAPIClient.h"

static NSString * TKUnderscoresToCamelCaseString(NSString *underscores) {
    NSMutableString *output = [NSMutableString string];
    BOOL makeNextCharacterUpperCase = NO;
    for (NSInteger idx = 0; idx < [underscores length]; idx += 1) {
        unichar c = [underscores characterAtIndex:idx];
        if (c == '_') {
            makeNextCharacterUpperCase = YES;
        } else if (makeNextCharacterUpperCase) {
            [output appendString:[[NSString stringWithCharacters:&c length:1] uppercaseString]];
            makeNextCharacterUpperCase = NO;
        } else {
            [output appendFormat:@"%C", c];
        }
    }
    return output;
}

static NSString* const kUpdatedAt = @"updatedAt";

static NSString * const kAPIBaseURLString = @"http://events.dev/events/505735ec529fa42e1200000e/";
//static NSString * const kAPIBaseURLString = @"http://events.10.10.11.251.xip.io/events/505735ec529fa42e1200000e/";

@interface EventsAPIClient ()

@property (nonatomic, strong) NSManagedObjectContext *backingManagedObjectContext;
@property (nonatomic, strong) NSMutableDictionary *entityNetworkRequestPolling;

- (NSString *)lastModifiedForObject:(NSManagedObject *)object;
- (NSString *)lastModifiedForObjectsOfClass:(Class)objectClass;

@end

@implementation EventsAPIClient

@synthesize backingManagedObjectContext=_backingManagedObjectContext;

+ (EventsAPIClient *)sharedClient {
    static EventsAPIClient *_sharedClient = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _sharedClient = [[self alloc] initWithBaseURL:[NSURL URLWithString:kAPIBaseURLString]];
    });
    
    return _sharedClient;
}

- (id)initWithBaseURL:(NSURL *)url {
    self = [super initWithBaseURL:url];
    if (!self) {
        return nil;
    }
    
    // 304 Not-Modified
    [AFJSONRequestOperation addAcceptableStatusCodes:[NSIndexSet indexSetWithIndex:304]];
    
    [self registerHTTPOperationClass:[AFJSONRequestOperation class]];
    [self setDefaultHeader:@"Accept" value:@"application/json"];
    
    [self setReachabilityStatusChangeBlock:^(AFNetworkReachabilityStatus status) {
        self.operationQueue.suspended = (status == AFNetworkReachabilityStatusNotReachable);
    }];
    
    self.supportRelationsByID = YES;
    self.entityNetworkRequestPolling = [NSMutableDictionary dictionary];
    
    return self;
}

- (NSString *)pathForEntity:(NSEntityDescription *)entity {
    // Remove Prefix 'E'
    NSString *name = [entity.name substringFromIndex:1];
    return AFPluralizedString(name);
}

- (NSDictionary *)attributesForRepresentation:(NSDictionary *)representation
                                     ofEntity:(NSEntityDescription *)entity
                                 fromResponse:(NSHTTPURLResponse *)response
{
    NSDictionary *keyMapping = nil;
    Class entityClass = NSClassFromString(entity.name);
    if ([entityClass respondsToSelector:@selector(mapping)]) {
        keyMapping = [entityClass performSelector:@selector(mapping)];
    }
    
    NSMutableDictionary *newRepresentation = [NSMutableDictionary dictionaryWithCapacity:representation.count];
    for (NSString *key in representation) {
        
        NSString *newKey = nil;
        if (keyMapping && keyMapping[key]) {
            newKey = keyMapping[key];
        } else {
            newKey = TKUnderscoresToCamelCaseString(key);
        }
        
        newRepresentation[newKey] = representation[key];
    }
    
    NSMutableDictionary *mutablePropertyValues = [[super attributesForRepresentation:newRepresentation ofEntity:entity fromResponse:response] mutableCopy];
    if ([entity.name isEqualToString:@"EAct"]) {
        //NSString *description = [representation valueForKey:@"description"];
        //[mutablePropertyValues setValue:description forKey:@"artistDescription"];
    }
    
    return mutablePropertyValues;
}

- (BOOL)shouldFetchRemoteAttributeValuesForObjectWithID:(NSManagedObjectID *)objectID inManagedObjectContext:(NSManagedObjectContext *)context {
    return NO;
    //return [[[objectID entity] name] isEqualToString:@"Artist"];
}

- (BOOL)shouldFetchRemoteValuesForRelationship:(NSRelationshipDescription *)relationship forObjectWithID:(NSManagedObjectID *)objectID inManagedObjectContext:(NSManagedObjectContext *)context {
    return NO;
    //return [[[objectID entity] name] isEqualToString:@"Artist"];
}

- (BOOL)shouldMakeNetworkRequestForFetchRequest:(NSFetchRequest *)fetchRequest
{
    static const NSTimeInterval kRelaxTime = 300; //5*60
    NSString *requestName = fetchRequest.entityName;
    NSDate *previousRequestDate = self.entityNetworkRequestPolling[requestName];
    NSDate *currentDate = [NSDate date];

    if (previousRequestDate && [previousRequestDate timeIntervalSinceDate:currentDate] < kRelaxTime) {
        NSLog(@"Polling: %@ - %@", requestName, previousRequestDate);
        return NO;
        //TODO: Would be nice here to make Backed request
    }
    
    self.entityNetworkRequestPolling[requestName] = currentDate;
    NSLog(@"Requesting: %@ - %@", requestName, currentDate);
    
    return YES;
}

- (NSMutableURLRequest *)requestForFetchRequest:(NSFetchRequest *)fetchRequest
                                    withContext:(NSManagedObjectContext *)context
{
    //Due Backing hack, not realy needed, but just in case
    if (fetchRequest.propertiesToFetch.count == 1 && [[[fetchRequest.propertiesToFetch objectAtIndex:0] name] isEqualToString:kUpdatedAt]) {
        return nil;
    }
    
    if (![self shouldMakeNetworkRequestForFetchRequest:fetchRequest]) return nil;
    
    static NSString * const kModifiedSinceHeader = @"If-Modified-Since";
    
    NSMutableURLRequest *request = [super requestForFetchRequest:fetchRequest withContext:context];
    
    //This is for testing real 304 responses
    // TODO: Check if needed
    request.cachePolicy = NSURLRequestReloadIgnoringCacheData;
    
    NSString *lastModified = [self lastModifiedForObjectsOfClass:NSClassFromString(fetchRequest.entity.name)];
    if (lastModified) [request setValue:lastModified forHTTPHeaderField:kModifiedSinceHeader];
    //return nil;
    return request;
}

#pragma mark - Getting Last-Updated-At

- (NSString *)lastModifiedFromDate:(NSDate *)date {
    // RFC1123
    static NSDateFormatter *timeDateFormatter = nil;
    
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        timeDateFormatter = [[NSDateFormatter alloc] init];
        timeDateFormatter.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
        timeDateFormatter.timeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];
        timeDateFormatter.dateFormat = @"EEE',' dd MMM yyyy HH':'mm':'ss 'GMT'";
    });
    return [timeDateFormatter stringFromDate:date];
}

- (NSDate *)lastUpdatedAtForObjectsOfClass:(Class)objectClass {
    
    // TODO: Think if better to store in User-Info
    
    NSString *entityName = NSStringFromClass(objectClass);
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];
    [request setFetchBatchSize:1];
    [request setFetchLimit:1];
    [request setSortDescriptors:@[[NSSortDescriptor sortDescriptorWithKey:kUpdatedAt ascending:NO]]];
    [request setPropertiesToFetch:@[kUpdatedAt]];
    
    NSManagedObjectContext *context = self.backingManagedObjectContext;
    NSArray *objects = [context executeFetchRequest:request error:NULL];
    NSManagedObject *obj = (objects.count > 0) ? objects[0] : nil;
    //NSManagedObject *obj = [objectClass MR_executeFetchRequestAndReturnFirstObject:request inContext:[NSManagedObjectContext MR_contextForCurrentThread]];
    return [obj valueForKey:kUpdatedAt];
}

- (NSString *)lastModifiedForObjectsOfClass:(Class)objectClass {
    return [self lastModifiedFromDate:[self lastUpdatedAtForObjectsOfClass:objectClass]];
}

- (NSString *)lastModifiedForObject:(NSManagedObject *)object {
    return [self lastModifiedFromDate:[object valueForKey:kUpdatedAt]];
}


#pragma mark - Backing context hack

- (NSManagedObjectContext *)backingManagedObjectContext {
    if (!_backingManagedObjectContext) {
        _backingManagedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
        AFIncrementalStore *store = (id)[NSPersistentStore MR_defaultPersistentStore];
        _backingManagedObjectContext.persistentStoreCoordinator = store.backingPersistentStoreCoordinator;
        //_backingManagedObjectContext.persistentStoreCoordinator = [NSPersistentStoreCoordinator MR_defaultStoreCoordinator];
        //_backingManagedObjectContext.retainsRegisteredObjects = YES;
    }
    
    return _backingManagedObjectContext;
}


@end

Podfile

platform :ios, '5.0'

# Core
pod 'AFIncrementalStore', :git => 'https://github.com/xslim/AFIncrementalStore' #, :head
pod 'MagicalRecord', :podspec => 'https://raw.github.com/magicalpanda/MagicalRecord/master/MagicalRecord.podspec'

# Helpers
pod 'ISO8601DateFormatter'
#pod 'AFHTTPRequestOperationLogger'
pod 'PonyDebugger', :head

# UI
pod 'TKThemeManager', :podspec => 'https://raw.github.com/xslim/TKThemeManager/master/TKThemeManager.podspec'
pod 'UIGlossyButton'
pod 'SVProgressHUD'
pod 'DDPageControl', '0.1'
pod 'JMTabView'
pod 'MHTabBarController', :podspec => 'https://raw.github.com/gist/3832321/14c550aa22b2d784f2e9b1fc06eea323ec8b6e26/MHTabBarController.podspec'

# Social
pod 'Facebook-iOS-SDK', '1.2'
pod 'ShareKit/Facebook'
pod 'ShareKit/Twitter'
pod 'FlurrySDK'

# Testing
pod 'TestFlightSDK'
pod 'DCIntrospect'