Decode JSON with different structures with Swift - json

Question

I have json data with the same core structure from a nosql database (PK, SK, attributes). The attributes part will be different depending on the value of SK.
Example:
[
{
"PK": "POLL#1544693DF0E88EC-3225-410E-B156-D13781B238F6",
"SK": "#METADATA#1544693DF0E88EC-3225-410E-B156-D13781B238F6",
"attributes": {
"latitude": "53.34589121858683",
"longitude": "-6.272215191675388",
"max_choices": 50,
"number": "1544693",
"poll_open": false,
}
},
{
"PK": "POLL#1544693DF0E88EC-3225-410E-B156-D13781B238F6",
"SK": "CHOICE#00a6ec5c-acc1-40f1-a087-31160d2cfc65",
"attributes": {
"distance": 790.95097525,
"latitude": 53.3416,
"price": "€€",
"categories": [
{
"title": "Ramen",
"alias": "ramen"
}
],
"vote_count": 0,
"longitude": -6.26274
}
}
]
Is it possible to use decode without errors? I've been stuck on this for hours.
I've defined the following:
struct Result: Codable {
var PK: String
var SK: String
var attributes: String
}
But, when I decode, I get the error:
typeMismatch(Swift.String, Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "attributes", intValue: nil)], debugDescription: "Expected to decode String but found a dictionary instead.", underlyingError: nil))
I just want to decode 'attributes' as a generic string and parse it later depending on the value of SK when I know how to properly handle it. Why is this so difficult?

Answer 1

Do you need attributes right now? Or are you just looking for pk and sk? If you do not need it just do not include
var attributes: String
in your struct. It will not have a decode error and it will decode the other two, you just will not get the attributes parameter. It is not able to decode the attributes
as a string because it is not. It is really more like a dictionary. Swift does not know how to handle that unless you specifically tell it. That being said you could always do this
struct Result: Codable {
var PK: String
var SK: String
var attributes: Attributes
}
struct Attributes: Codable {
var lattitude: String
var longitude: String
//and whatever else you know you have
}
the key is only adding the values you know will be included in the attributes or else it will give an error

Answer 2

You need to handle this using JSONSerialization instead of Codable. Given you still want to use the same struct you need to change it to
struct Result {
var PK: String
var SK: String
var attributes: [String: Any]
}
and decode the json like this
var result: Result?
do {
if let dictionary = try JSONSerialization.jsonObject(with: data) as? [String: Any],
let pk = dictionary["PK"] as? String,
let sk = dictionary["SK"] as? String,
let attributes = dictionary["attributes"] as? [String: Any] {
result = Result(PK: pk, SK: sk, attributes: attributes)
}
} catch {
print(error)
}
Now you still need to convert the attributes ([String: Any]) property of Result to something more usable but that is beyond this question