Parse valid objects from JSON array in Swift - ios

Question

I have a codable struct like this
struct User: Codable {
let id: String
let registrationId: String
let firstName: String?
let lastName: String?
}
Now, the response from the server contains an array like this
[
{
"id": "1",
"registrationId": "r1",
"firstName": "Jon",
"lastName": "Doe"
},
{
"id": "2",
"registrationId": null,
"firstName": null,
"lastName": null
},
{
"id": "3",
"registrationId": null,
"firstName": null,
"lastName": null
},
{
"id": "4",
"registrationId": "r4",
"firstName": "Jon",
"lastName": "Snow"
}
]
I want to parse this as [User] but only those who have a valid(not null) registrationId. I know how to parse JSON in swift. But the problem here is because of the two invalid data in the middle the whole response will run into decoding error. But I want to parse it as an array of [User] containing valid ones(in this case first and last object).
Any hints or help is much appreciated.

Answer 1

1- Make registrationId an optional
let registrationId: String?
2-
let res = try JSONDecoder().decode([User].self,from:data)
let filtered = res.filter { $0.registrationId != nil }

Answer 2

after all, this data must come from a database or an array. By making the id parameter as the primary key, the registrationId parameter as a foreign key, and if you are working on the registrationId parameter, you can make a productive sequence or if it is on the array, you can link the method that generates the sequence for that registrationId.

Answer 3

Now I know how to achieve this.
struct User: Codable {
let id: String
let registrationId: String
let firstName: String?
let lastName: String?
}
struct WrappedDecodableArray<Element: Decodable>: Decodable {
let elements: [Element]
init(from decoder: Decoder) throws {
var container = try decoder.unkeyedContainer()
var elements = [Element]()
while !container.isAtEnd {
if let element = try? container.decode(Element.self) {
elements.append(element)
} else {
// move the container currentIndex forward
_ = try container.decode(Block.self)
}
}
self.elements = elements
}
private struct Block: Decodable {}
}
func testUserParsing() {
let jsonStr = """
[
{
"id": "1",
"registrationId": "r1",
"firstName": "Jon",
"lastName": "Doe"
},
{
"id": "2",
"registrationId": null,
"firstName": null,
"lastName": null
},
{
"id": "3",
"registrationId": null,
"firstName": null,
"lastName": null
},
{
"id": "4",
"registrationId": "r4",
"firstName": "Jon",
"lastName": "Snow"
}
]
"""
let jsonData = jsonStr.data(using: .utf8)!
let wrappedArray = try! JSONDecoder().decode(WrappedDecodableArray<User>.self, from: jsonData)
print(wrappedArray.elements)
}
It would have been more elegant if we could override the init(from decoder: Decoder) for Array under certain conditions like extension Array where Element == User. But looks like this is not possible. Initializer inside the extension can not override the original one and hence never get called.
So for now looks like wrapping with a struct is the only solution.