Create nested JSON in Objective-C - objective-c

Question

I'm trying to create JSON that looks like this:
{
"id": "feed/http://feeds.feedburner.com/design-milk",
"title": "Design Milk",
"categories": [
{
"id": "user/category/test",
"label": "test"
}
]
}
I'm doing it with this method:
NSMutableDictionary *req = [NSMutableDictionary #"feed/http://feeds.feedburner.com/design-milk" forKey:#"id"];
[req #"Design Milk" forKey:#"title"];
NSDictionary *tmp = [[NSDictionary alloc] initWithObjectsAndKeys:
#"user/category/test", #"id", #"test", #"label",
nil];
[req setObject:tmp forKey:#"categories"];
NSData *postdata = [NSJSONSerialization dataWithJSONObject:req options:0 error:&error];
However, this isn't working. What am I doing wrong here?

Answer 1

The first line of your code isn't going to compile, so you need to fix that.
The value of "categories" in your example output is an array with one element, which happens to be a dictionary. So you need
NSDictionary* oneCategory = [NSDictionary dictionaryWithObjectsAndKeys:...];
NSArray* categories = [NSArray arrayWithObject:oneCategory];
[req setObject:categories forKey:#"categories"];
And you should really use more modern syntax, like
req [#"categories"] = #[oneCategory];

Answer 2

You were missing an array:
NSMutableDictionary *req =[NSMutableDictionary dictionaryWithObjectsAndKeys:#"feed/http://feeds.feedburner.com/design-milk", #"id", nil];
req[#"title"] = #"Design Milk";
NSDictionary *tmp = [[NSDictionary alloc] initWithObjectsAndKeys:
#"user/category/test", #"id",
#"test", #"label",
nil];
NSMutableArray *arr = [[NSMutableArray alloc] init];
[arr addObject:tmp];
[req setObject:arr forKey:#"categories"];
NSError *error;
NSData *postdata = [NSJSONSerialization dataWithJSONObject:req options:0 error:&error];