convenient-fetch.m

@interface MyManagedObjectContext : NSManagedObjectContext

- (instancetype)main;
- (instancetype)newBackground;
- (instancetype)newUI;

- (NSArray *)fetch:(id)query;
- (id)fetchFirst:(id)query;

@end

@interface MyQuery : NSObject

@property (nonatomic, strong) NSEntityDescription *entity;
@property (nonatomic, strong) NSPredicate *predicate;

@end

@interface NSManagedObject ()

+ (MyQuery *)any;
+ (MyQuery *)all;
+ (MyQuery *)match:(id)predicate, ...;

@end

@interface Person : NSManagedObject

@end

static NSString *kNameAttr = @"name";

void sample() {
    MyManagedObjectContext *context;
    Person *any = [context fetchFirst:Person.any];
    NSArray *johns = [context fetch:[Person match:@"%K = %@", kNameAttr, @"John"]];
}