CODEWITHSUNDEEP
iosswiftxcodeswift3generic-programming
Hoang Trung
Hoang Trung

Reputation: 263

iOS - Swift: How to write generic function for this case?

I'm using CoreData in my app. There're 4 tables in the database: User, Medicine, Schedule and Patient. For each table I need to write an Add function to add data into the database like this: 

func addUser(email: String, password: NSData, handler: @escaping (_ status: SaveStatus, _ error: NSError?) -> Void){
    let managedContext = (UIApplication.shared.delegate as? AppDelegate)?.managedObjectContext
    let entity = NSEntityDescription.entity(forEntityName: DB.TABLE.USER, in: managedContext!)!
    let nurse = NSManagedObject(entity: entity, insertInto: managedContext) as! User
    nurse.email = email
    nurse.password = password

    save { (status, error) in
        handler(status, error)
    }
}

func addMedicine(name: String, handler: @escaping(_ status: SaveStatus, _ error: NSError?) -> Void){
    let managedContext = (UIApplication.shared.delegate as? AppDelegate)?.managedObjectContext
    let entity = NSEntityDescription.entity(forEntityName: DB.TABLE.MEDICINE, in: managedContext!)!
    let medicine = NSManagedObject(entity: entity, insertInto: managedContext) as! Medicine
    medicine.name = name

    save { (status, error) in
        handler(status, error)
    }
}

and so on ...

I want to write an generic function like this:

func addDataToDB<DATA>(object: DATA, handler: @escaping SaveStatusHandler){
    switch DATA {
    case DATA is LoginData:
        break
    default:
        break
    }
}

I don't know what type should the LoginData be, so I can compare the DATA with it. Or is there any better way to do this?

Upvotes: 2

Views: 111

Answers (1)

Luca D&#39;Alberti
Luca D&#39;Alberti

Reputation: 4849

The fastest solution for this case, since each Entity has a different save implementation, is to declare a Saveable protocol

protocol Saveable {
    associatedtype Parameters
    static var entityName: String { get }
    static var context: NSManagedContext { get }
    func setup(with parameters: Parameters)
    func save(_ handler: () -> ())
}

And then use this protocol as generic parameter in the addDataToDB function

func addDataToDB<T>(params: T.Parameters, _ handler: () -> ()) where T: Saveable {
    let entity = NSEntityDescription.entity(forEntityName: T.entityName, in: T.contenxt)!
    let object = NSManagedObject(entity: entity, insertInto: T.context) as! T
    object.setup(with: params)

    object.save(handler)
}

Parameters in this case should be a struct for example, or a dictionary, it's completely up to you

Upvotes: 1

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