How to use generics and inheritance to parse an output? - swift

Question

I'm programming a network call for a backend in NestJs which has pagination enabled. The output of the service has the following structure:
{
"items": [{
"id": "26c26ecb-0763-4813-b489-3c6ad94084a9",
"body": "Test body",
"subTitle": "SubTitle Test",
"author": "Test Author",
"createAt": "2023-01-12T07:04:58.480Z",
"title": "Temporary Title",
"updateAt": "2023-01-12T07:04:58.480Z"
}],
"meta": {
"itemsPerPage": 10,
"totalPages": 2,
"currentPage": 1,
"totalItems": 19,
"itemCount": 10
},
"links": {
"previous": "",
"first": "\/post\/public?limit=10",
"next": "\/post\/public?page=2&limit=10",
"last": "\/post\/public?page=2&limit=10"
}
}
The Meta and Links atribute are fairly straight through so they have no problems. The issue that i'm having is the items list. The objects data structures that are inside can be different, there can be News, Posts, Events.
All of this objects have some properties in common so a BaseEntity Model was created. Therefore all models inherit from BaseEntity.
I dont want to create a class for each of this outputs. I want to declare a generic class that receives a generic an parses it accordingly.
My BaseCrudEntity model and protocol are designed like this:
public protocol BaseCrudEntityParsingProtocol: AnyObject
{
var id: String { get set }
var createAt: Date { get set }
var updateAt: Date { get set }
var deletedAt: Date? { get set }
var isActive: Bool { get set }
init()
init?(info: Any?)
static func parseList(info: Any?) -> [BaseCrudEntityParsingProtocol]?
}
public extension BaseCrudEntityParsingProtocol
{
static func parseList(info: Any?) -> [BaseCrudEntityParsingProtocol]? {
return nil
}
}
public class BaseCrudEntity: BaseCrudEntityParsingProtocol
{
public var createAt: Date = Date()
public var updateAt: Date = Date()
public var deletedAt: Date?
public var isActive: Bool = true
public var id: String = ""
enum CodingKeysBase: String {
case createAt = "createAt"
case updateAt = "updateAt"
case deletedAt = "deletedAt"
case isActive = "isActive"
case id = "id"
}
required public init() { }
required public init?(info: Any?) {
guard let anyInfo = info,
let info = anyInfo as? NSDictionary else { return nil }
self.createAt = info.parseString(forKeyPath: CodingKeysBase.createAt.rawValue).toDate()
self.updateAt = info.parseString(forKeyPath: CodingKeysBase.updateAt.rawValue).toDate()
self.deletedAt = info.parseStringOptional(forKeyPath: CodingKeysBase.deletedAt.rawValue)?.toDateOptional()
self.isActive = info.parseBool(forKeyPath: CodingKeysBase.isActive.rawValue)
self.id = info.parseString(forKeyPath: CodingKeysBase.id.rawValue)
}
}
And an example of a specific model which will have pagination looks like this:
// MARK: - Post
public class Post: BaseCrudEntity
{
public var title: String?
public var subTitle: String?
public var author: String?
public var body: String?
enum CodingKeys: String, CodingKey {
case title = "title"
case subTitle = "subTitle"
case author = "author"
case body = "body"
}
required public init() {
super.init()
}
required public init?(info: Any?) {
super.init(info: info)
guard let anyInfo = info,
let info = anyInfo as? NSDictionary else { return nil }
self.title = info.parseStringOptional(forKeyPath: CodingKeys.title.rawValue)
self.subTitle = info.parseStringOptional(forKeyPath: CodingKeys.subTitle.rawValue)
self.author = info.parseStringOptional(forKeyPath: CodingKeys.author.rawValue)
self.body = info.parseStringOptional(forKeyPath: CodingKeys.body.rawValue)
}
public static func parseList(info: Any?) -> [Post]? {
guard let anyInfo = info,
let rawList = anyInfo as? [NSDictionary] else { return nil }
return rawList.compactMap(Post.init)
}
}
I've created the following class so that I can pass a generic value and parse it accordingly, the problem that i'm having is that the items list returns nil, as if the parsing cannot be done successfully or is having problems. This task could be done using the Codable protocol but due to the codebase design it cannot be done at this time.
public class PaginatedList<Body: BaseCrudEntity> where Body: BaseCrudEntity
{
public var items: [Body]?
public var meta: PaginatedListMeta?
public var links: PaginatedListLinks?
enum CodingKeys: String, CodingKey {
case meta = "meta"
case links = "links"
case items = "items"
}
public init() {
}
public init(items: [Body]?, meta: PaginatedListMeta?, links: PaginatedListLinks?) {
self.meta = meta
self.links = links
}
public init?(info: Any?) {
guard let anyInfo = info,
let info = anyInfo as? NSDictionary else { return nil }
self.meta = PaginatedListMeta(info: info[CodingKeys.meta.rawValue])
self.links = PaginatedListLinks(info: info[CodingKeys.links.rawValue])
self.items = Body.parseList(info: info[CodingKeys.items.rawValue]) as? [Body]
}
}
I've tried a couple of solutions but none seem to work.