Error with NSJSONSerialization – Invalid type in JSON write (Menu)

That’s because your “Menu” class is not serializable in JSON. Bascially the language doesn’t know how your object should be represented in JSON (which fields to include, how to represent references to other objects…)

From the NSJSONSerialization Class Reference

An object that may be converted to JSON must have the following
properties:

• The top level object is an NSArray or NSDictionary.
• All objects are instances of NSString, NSNumber, NSArray, NSDictionary, or NSNull.
• All dictionary keys are instances of NSString.
• Numbers are not NaN or infinity.

This means that the language knows how to serialize dictionaries. So a simple way to get a JSON representation from your menu is to provide a Dictionary representation of your Menu instances, which you will then serialize into JSON:

- (NSDictionary *)dictionaryFromMenu:(Menu)menu {
    [NSDictionary dictionaryWithObjectsAndKeys:[menu.dateUpdated description],@"dateUpdated",
    menu.categoryId, @"categoryId",
    //... add all the Menu properties you want to include here
    nil];
}

And you could will use it like this :

NSDictionary *menuDictionary = [self dictionaryFromMenu:[[DataStore singleton] getHomeMenu]]; 

NSError *err;
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:menuDictionary options:NSJSONWritingPrettyPrinted error:&err];

NSLog(@"JSON = %@", [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding]);