How to store JSON decodable values into Coredata using Swift

问题

I am trying to load JSON Data into CoreData. Here, I used JSON structure for decodable and after that I am trying to fetch the decodable Data into CoreData. I don’t know how to use decodable with iterate the data and fetching into coredata. Below code I tried, but not getting proper result. Please help me to resolve this.

My JSON

{
    "status": true,
    "data": [
        {
            "id": "20",
            "name": "ar1"
        },
        {
            "id": "21",
            "name": "ar2"
        },
        {
            "id": "22",
            "name": "ar3"
        }
    ]
}

My Structure For JSON

struct userList: Codable {
    let status: Bool
    let data: [userData]
}

struct userData: Codable {
    let id, name: String
}

My Coredata Entity

var users = [User]() // User is my entity name

JSON Codable and Try ing to Load Into CoreData

do {
       let result = try JSONDecoder().decode(userList.self, from:data) // here I am dong mistakes.
       let status = result.status
       if status == true {
           let newPerson = User(context: self.context)
           newPerson.id = "" // Cant able to get values
           newPerson.name = ""
           self.users.append(newPerson)

            DispatchQueue.main.asyncAfter(deadline: .now() + 0.5) {
                self.tableView.reloadData()
             }
            } else {
               print(error)
             }

    } catch {
         print(error)
}

回答1:

To be able to decode JSON directly into Core Data classes you have to adopt Decodable

Implement two extensions to be able to pass the managed object context via the JSONDecoder

extension CodingUserInfoKey {
    static let context = CodingUserInfoKey(rawValue: "context")!
}

extension JSONDecoder {
    convenience init(context: NSManagedObjectContext) {
        self.init()
        self.userInfo[.context] = context
    }
}

In User adopt Decodable and add CodingKeys and the required init(from method

public class User: NSManagedObject, Decodable {

    private enum CodingKeys: String, CodingKey { case name, id }

    public required convenience init(from decoder: Decoder) throws {
        guard let context = decoder.userInfo[.context] as? NSManagedObjectContext else { fatalError("Error: with managed object context!") }
        let entity = NSEntityDescription.entity(forEntityName: "User", in: context)!
        self.init(entity: entity, insertInto: context)
        let values = try decoder.container(keyedBy: CodingKeys.self)
        name = try values.decode(String.self, forKey: .name)
        id = try values.decode(String.self, forKey: .id)
    }
...

Now you need only one umbrella struct for the root object. Once again please name structs always with starting uppercase letter
```
struct Root: Decodable {
    let status: Bool
    let data: [User]
}
```

To decode the JSON use the custom initializer, the User instances are inserted automatically into the database

do {
    let decoder = JSONDecoder(context: context) // context is the NSManagedObjectContext instance 
    let result = try decoder.decode(Root.self, from: data)
    if result.status {
       print("success")
       try context.save()
    }  
catch { print(error)

来源：https://stackoverflow.com/questions/59629695/how-to-store-json-decodable-values-into-coredata-using-swift

标签

ios

json

swift

core-data