Objective-C Object Association for JSON Model

Model+AdditionalParam.h

@interface Model (AdditionalParam)
  
@property (nonatomic, strong) NSString <Optional> * new_key_name;

@end

Model+AdditionalParam.m

#import "Model+AdditionalParam.h"
#import <objc/runtime.h>

#define kNew_key_name @"new_key_name"

@implementation Card (Keys)

- (void)setNew_key_name:(NSString *)value {
    objc_setAssociatedObject(self, kNew_key_name, value, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (NSString *)new_key_name {
    return objc_getAssociatedObject(self, kNew_key_name);
}

@end