// fetch all -> filter by predicate
@interface RequestInMemory : NSObject
@property(nonatomic, strong) NSArray *fetchedContents;

// initialize class + fetch data from CoreData
+ (instancetype)memoryEntityDescription:(NSEntityDescription *) entityDescription context:(NSManagedObjectContext *) managedObjectContext;

+ (instancetype)memoryEntityDescription:(NSEntityDescription *) entityDescription predicate:(NSPredicate *) predicate context:(NSManagedObjectContext *) managedObjectContext;

#pragma mark - manually


// manually update internal database
// when initialize the class, automatically call this method.
- (NSArray *)fetchAll;

- (NSArray *)fetchWithPredicate:(NSPredicate *) predicate;

#pragma mark - filter helper

- (BOOL)testWithPredicate:(NSPredicate *) predicate;

- (NSArray *)findFirstWithPredicate:(NSPredicate *) predicate;

- (NSArray *)findAllWithPredicate:(NSPredicate *) predicate;

@end

- (void)viewDidAppear:(BOOL) animated {
    [super viewDidAppear:animated];
    CFTimeInterval startTime = CACurrentMediaTime();
    {
        for (size_t i = 0; i < 1000; i++) {
            @autoreleasepool {
                [self performCoreData];
            }
        }
    }
    CFTimeInterval endTime = CACurrentMediaTime();
    NSLog(@"Total Runtime performCoreData: %g s", endTime - startTime);
    CFTimeInterval startTime_b = CACurrentMediaTime();
    {
        self.personInMemory = [RequestInMemory memoryEntityDescription:[Person MR_entityDescription] context:[NSManagedObjectContext MR_defaultContext]];
        for (size_t i = 0; i < 1000; i++) {
            @autoreleasepool {
                [self performRequestInMemory];
            }
        }
    }
    CFTimeInterval endTime_b = CACurrentMediaTime();
    NSLog(@"Total Runtime performRequestInMemory: %g s", endTime_b - startTime_b);
}

- (void)performRequestInMemory {
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K == %d", @"age", 10];
    [self.personInMemory findFirstPredicate:predicate];
}

- (void)performCoreData {
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"%K == %d", @"age", 10];
    [Person MR_findFirstWithPredicate:predicate];
}