An NSObject category for when you're working with it converting to/from JSON.

Installation

In your Podfile, add this line:

pod "MTJSONUtils"

Methods

Use the following for a shortcut to generating JSON data from a dictionary (or any NSObject):

- (NSData *)JSONData;

The requirements of NSJSONSerialization state that all objects must be instances of NSString, NSNumber, NSArray, NSDictionary, or NSNull. The following can be called on any NSObject and will return a safe deep copy of the receiver:

- (id)objectWithJSONSafeObjects;

This will:

• Replace NSDate objects with their ISO string representation. (e.g. 2012-08-12T04:17:30Z)
• Replace any other non-valid objects with their string description.
• More coming...

The following methods allow you to query into an object graph that includes arrays (not just dictionaries):

- (id)valueForComplexKeyPath:(NSString *)keyPath;
- (NSString *)stringValueForComplexKeyPath:(NSString *)key;

Available Subscripting Values:

• 0..infinity
• first
• last

Example

Given this object:

NSDictionary *dictionary = @{
    @"parent" : @{
        @"name" : @"Nathan",
        @"children" : @[ @{
            @"name" : @"adam",
            @"apple_products" : @[ @{
                @"title"        : @"macbook",
                @"price"        : @1399.99,
                @"date_bought"  : [NSDate dateWithTimeInterval:-22342 sinceDate:[NSDate date]]
            },
            @{
                @"title"        : @"mac mini",
                @"price"        : @599.99,
                @"date_bought"  : [NSDate dateWithTimeInterval:-30223 sinceDate:[NSDate date]]
            },
            @{
                @"title"        : @"iphone",
                @"price"        : @199.99,
                @"date_bought"  : [NSDate dateWithTimeInterval:-123453 sinceDate:[NSDate date]]
            }]
        },
        @{
            @"name" : @"amanda",
            @"apple_products" : @[ @{
                @"title"        : @"nano",
                @"price"        : @299.99,
                @"date_bought"  : [NSDate dateWithTimeInterval:-123453 sinceDate:[NSDate date]]
            }]
        },
        @{
            @"name" : @"andrew",
            @"apple_products" : @[ @{
                @"title"        : @"ipad",
                @"price"        : @499.99,
                @"date_bought"  : [NSDate dateWithTimeInterval:-2452342 sinceDate:[NSDate date]]
            },
            @{
                @"title"        : @"ipod touch",
                @"price"        : @399.99,
                @"date_bought"  : [NSDate dateWithTimeInterval:-430223 sinceDate:[NSDate date]]
            }]
        }]
    }
};

You could query the values like this:

[[dictionary valueForComplexKeyPath:@"parent.name"]                                         // => "Nathan"
[[dictionary valueForComplexKeyPath:@"parent.children[0].name"]                             // => "adam"
[[dictionary valueForComplexKeyPath:@"parent.children[1].name"]                             // => "amanda"
[[dictionary valueForComplexKeyPath:@"parent.children[2].name"]                             // => "andrew"
[[dictionary valueForComplexKeyPath:@"parent.children[first].name"]                         // => "adam"
[[dictionary valueForComplexKeyPath:@"parent.children[last].name"]                          // => "andrew"
[[dictionary valueForComplexKeyPath:@"parent.children[first].apple_products[0].title"]      // => "macbook"
[[dictionary valueForComplexKeyPath:@"parent.children[first].apple_products[1].title"]      // => "mac mini"
[[dictionary valueForComplexKeyPath:@"parent.children[first].apple_products[2].title"]      // => "iphone"
[[dictionary valueForComplexKeyPath:@"parent.children[first].apple_products[last].title"]   // => "iphone"
[[dictionary valueForComplexKeyPath:@"parent.children[last].apple_products[last].title"]    // => "ipod touch"
[[dictionary valueForComplexKeyPath:@"parent.children[last].apple_products[last].price"]    // => 399.99

Misc

And some nifty macros for dealing with NSNull and nil:

// swaps NSNull for nil
#define NILL(a) ([a isKindOfClass:[NSNull class]] ? nil : a)
// swaps nil for NSNull
#define NUL(a) a ? a : [NSNull null]