NSObject category for handling JSON dictionaries. Described in detail at http://www.cimgf.com/2012/01/11/handling-incoming-json-redux/

NSObject+setValuesForKeysWithJSONDictionary.h

//
//  NSObject+setValuesForKeysWithJSONDictionary.h
//  SafeSetDemo
//
//  Created by Tom Harrington on 12/29/11.
//  Copyright (c) 2011 Atomic Bird, LLC. All rights reserved.
//
//  Modified by Julien Grimault
//

#import <Foundation/Foundation.h>


@interface NSObject (setValuesForKeysWithJSONDictionary)

/*
 for each property of self, a lookup is made on the |propertiesMapping| dictionary to get the key to use in the |keyedValues| dictionary. If no entry is found in propertiesMapping, the property name is used directly.
 propertiesMapping uses the property name as key and the keyedValues key as value.
 */
- (void)setValuesForKeysWithJSONDictionary:(NSDictionary *)keyedValues
                         propertiesMapping:(NSDictionary*)propertiesMapping
                             dateFormatter:(NSDateFormatter *)dateFormatter;

- (void)setValuesForKeysWithJSONDictionary:(NSDictionary *)keyedValues
                             dateFormatter:(NSDateFormatter *)dateFormatter;

@end

NSObject+setValuesForKeysWithJSONDictionary.m

//
//  NSObject+setValuesForKeysWithJSONDictionary.m
//  SafeSetDemo
//
//  Created by Tom Harrington on 12/29/11.
//  Copyright (c) 2011 Atomic Bird, LLC. All rights reserved.
//
//  Modified by Julien Grimault
//

#import "NSObject+setValuesForKeysWithJSONDictionary.h"
#import <objc/runtime.h>
#import <objc/message.h>

@implementation NSObject (setValuesForKeysWithJSONDictionary)

- (void)setValuesForKeysWithJSONDictionary:(NSDictionary *)keyedValues
                             dateFormatter:(NSDateFormatter *)dateFormatter
{
  return [self setValuesForKeysWithJSONDictionary:keyedValues
                                propertiesMapping:nil
                                    dateFormatter:dateFormatter];
}

- (void)setValuesForKeysWithJSONDictionary:(NSDictionary *)keyedValues
                         propertiesMapping:(NSDictionary*)propertiesMapping
                             dateFormatter:(NSDateFormatter *)dateFormatter
{  
  
  //we need to go up the inheritance tree to assign the properties declared in the superclass
  //we must however assign the properties starting with the root class and ending with [self class],
  //this is to ensure that the overriden properties are assigned correctly
  NSMutableArray* inheritanceTree = [NSMutableArray array];
  Class currentClass = [self class];
  while (currentClass) {
    [inheritanceTree addObject:currentClass];
    currentClass = class_getSuperclass(currentClass);
  }
  
  [inheritanceTree enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(Class objectClass, NSUInteger idx, BOOL* stop){
    unsigned int propertyCount;
    objc_property_t *properties = class_copyPropertyList(objectClass, &propertyCount);
    
    /*
     This code iterates over self's properties instead of ivars because the backing ivar might have a different name
     than the property, for example if the class includes something like:
     
     @synthesize foo = foo_;
     
     In this case what we really want is "foo", not "foo_", since the incoming keys in keyedValues probably
     don't have the underscore. Looking through properties gets "foo", looking through ivars gets "foo_".
     */
    for (int i=0; i<propertyCount; i++) {
      objc_property_t property = properties[i];
      const char *propertyName = property_getName(property);
      NSString* keyName = [NSString stringWithUTF8String:propertyName];
      
      //apply mapping
      NSString *keyNameJSON = keyName; //default if there is no mapping provided
      if (propertiesMapping) {
        NSString* mapping = [propertiesMapping objectForKey:keyName];
        if (mapping) {
          keyNameJSON = mapping;
        }
      }
      
      id value = [keyedValues objectForKey:keyNameJSON];
      if (value != nil) {
        char *typeEncoding = NULL;
        typeEncoding = property_copyAttributeValue(property, "T");
        
        if (typeEncoding == NULL) {
          continue;
        }
        switch (typeEncoding[0]) {
          case '@':
          {
            // Object
            Class propertyClass = nil;
            if (strlen(typeEncoding) >= 3) {
              char *propertyClassName = strndup(typeEncoding+2, strlen(typeEncoding)-3);
              propertyClass = NSClassFromString([NSString stringWithUTF8String:propertyClassName]);
              free(propertyClassName);
            }
            // Check for type mismatch, attempt to compensate
            if ([propertyClass isSubclassOfClass:[NSString class]] && [value isKindOfClass:[NSNumber class]]) {
              value = [value stringValue];
            } else if ([propertyClass isSubclassOfClass:[NSNumber class]] && [value isKindOfClass:[NSString class]]) {     
              //check if the value is yes,true,no or false..
              if ([value caseInsensitiveCompare:@"yes"] == NSOrderedSame || 
                  [value caseInsensitiveCompare:@"true"] == NSOrderedSame) {
                value = [NSNumber numberWithBool:YES];
              } else if ([value caseInsensitiveCompare:@"no"] == NSOrderedSame || 
                         [value caseInsensitiveCompare:@"false"] == NSOrderedSame) {
                value = [NSNumber numberWithBool:NO];
              } else {
                // If the ivar is an NSNumber we really can't tell if it's intended as an integer, float, etc.
                NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
                [numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
                value = [numberFormatter numberFromString:value]; 
              }
            } else if ([propertyClass isSubclassOfClass:[NSDate class]] && [value isKindOfClass:[NSString class]]) {
              if (dateFormatter) {
                value = [dateFormatter dateFromString:value];
              } else {
                NSTimeInterval interval = [value doubleValue];
                if (interval != 0.0) {
                  value = [NSDate dateWithTimeIntervalSince1970:interval];
                }
              }
            } else if ([propertyClass isSubclassOfClass:[NSURL class]] && [value isKindOfClass:[NSString class]]) {
              value = [NSURL URLWithString:value];
            }
            
            break;
          }
            
          case 'i': // int
          case 's': // short
          case 'l': // long
          case 'q': // long long
          case 'I': // unsigned int
          case 'S': // unsigned short
          case 'L': // unsigned long
          case 'Q': // unsigned long long
          case 'f': // float
          case 'd': // double
          case 'B': // BOOL
          {
            if ([value isKindOfClass:[NSString class]]) {
              NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
              [numberFormatter setNumberStyle:NSNumberFormatterDecimalStyle];
              value = [numberFormatter numberFromString:value];
            }
            break;
          }
            
          case 'c': // char
          case 'C': // unsigned char
          {
            if ([value isKindOfClass:[NSString class]]) {
              char firstCharacter = [value characterAtIndex:0];
              value = [NSNumber numberWithChar:firstCharacter];
            }
            break;
          }
            
          default:
          {
            DDLogError(@"Unknown type engonding %c",typeEncoding[0]);
            break;
          }
        }
        [self setValue:value forKey:keyName];
        free(typeEncoding);
      }
    }
    free(properties);
  }];
}

@end