Key value coding failure - ios

Question

So I have some json in a file like so
{
"address": {
"home": {
"street": "A Street"
}
}
}
I pull out the json string like so
NSString *string = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:nil];
NSData *data = [string dataUsingEncoding:NSUTF8StringEncoding];
I want to change a value on the fly, using a key path, so I need to make a deep mutable copy of the structure. So I am doing it like so
id json = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];
data = [NSKeyedArchiver archivedDataWithRootObject:json];
json = [NSKeyedUnarchiver unarchiveObjectWithData:data];
Using breakpoints I can see the json and it all looks fine. However, I get a crash on this line
[json setValue:#"Different Street" forKeyPath:#"address.home.street"];
The compiler suggested there isn't a key at this key path that conforms to key-value coding.
Annoyingly, this line works fine and returns the street string
id value = [json valueForKeyPath:#"address.home.street"];
Why can't I set a value like this?
Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__NSDictionaryI 0x1741bb580> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key pan.'

Answer 1

Use NSJSONReadingMutableContainers when reading your JSON. By default your containers are read in as immutable containers.
id json = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments|NSJSONReadingMutableContainers error:nil];