Unit testing JSON Swift - json

Question

I am working on an iOS application written in Swift which parse a lot of JSON files.
The JSON structures are sophisticated and I would to test them before to map JSON to object.
For example test if the key 'users' exists and for each user the structure('name', 'first', 'last').
{
"users": [
{
"name": {
"first": "emmi",
"last": "wiita"
}
},
{
"name": {
"first": "erdi",
"last": "nielen"
}
},
{
"name": {
"first": "daniel",
"last": "beck"
}
}
]
}
Are there any good way to do this?
Thanks.

Answer 1

The only way to accomplish that is really opening the JSON file and testing each property.
A good news is that since Swift 2.0 you can use guard to test if you can assign a valid value to a var or let, so you can create a function as follows:
func isValidJSON(data: NSData) -> Bool {
json = try NSJSONSerialization.JSONObjectWithData(data, options: .AllowFragments)
// if "users" exists on the JSON
// AND we can cast it to an array of dictionaries
guard let users = json["users"] as [[String: AnyObject]] else {
return false
}
for user in users {
guard let name = user["name"] as [[String: AnyObject]]
firstName = name["first"] as String,
lastName = name["last"] as String else {
return false
}
}
// valid JSON
return true
}
A best practice would be also to implement the use of Exceptions instead returning false in each guard statement.

Answer 2

Thank you for your post #Felipe Plets. I found a good way to test JSON file.
I have implemented an enum ErrorType(Exception):
/**
Enumeration describing possible errors that occur while parsing
a message from JSON file.
*/
enum ReceiverError: ErrorType {
/**
Error trigge when the key is missed or the type.
- Parameter key: Key missed.
*/
case MissingKeyOrType(key: String)
}
then I can test all the JSON file like this:
func isValidJSON(message: [String: AnyObject]) -> throws {
guard let sosId = message["id"] as? String
else { throw ReceiverError.MissingKeyOrType(key: "sos - id") }
guard let text = message["text"] as? String
else { throw ReceiverError.MissingKeyOrType(key: "text")
}
let json = ... Get JSON
do {
try isValidJSON(json)
} catch CustomReceiver.ReceiverError.MissingKeyOrType(let key) {
print("Error: Missing key or type [key: \(key)].")
}