从用于 CRUD 的 Firebase Firestore 的通用 swift 声明获取 @DocumentID id 的问题

Question

Models have been declared with an @DocumentID var id: String? Property and on update or delete methods I get error:

"Type of expression is ambiguous without more context"

All model adopt the same protocol which is the type the Generic expects when passing obj.

Anyone have any insight or idea as to how to get the id from a generic? Has anyone encountered this issue?

func remove(_ obj:T)
{
  guard let documentID = obj.id else { return }
  
    self.collection.document(documentID).delete
  {
    error in
    if let error = error
    {
      print("Unable to remove \(error.localizedDescription).")
    }
  }
}

Issue 2: due to another issue regarding parameter initialization before self available I am trying to initialize the generic firestorm in a view model:

    class ProtosListViewModel<T: Decodable, ObservableObject>
    {
        @Published var firestoreManager:FirestoreManager<T> where T:ProtoType
    
    init()
    {
        let protoType = ProtoType(collectionPath: "protoName")
        self.firestoreManager = FirestoreManager(database: Firestore.firestore(), firestoreType: protoType)
    }
}

and getting error: "Type 'T' does not conform to protocol 'ProtoType'"

All insight and support greatly appreciated! Thank you!

Answer 1

Regarding issue #1:

Instead of trying to create a generic function, I would create a remove function within each ViewModel (per model) individually. Additional to the issues you observe right now, you also have to tell firebase in which collection you want to remove the item:

db.collection ("collectionNameInFirebase") .document(documentID).delete()

The follwoing code is coming from the firebase documentation, you see a defined collection (in this case "cities"), that is missing in you function call, even if you make the other stuff work, you would also have to add this information.

private func deleteDocument() {
    // [START delete_document]
    db.collection("cities").document("DC").delete() { err in
        if let err = err {
            print("Error removing document: \(err)")
        } else {
            print("Document successfully removed!")
        }
    }
    // [END delete_document]
}

Regarding issue #2:

My classes start with creating constants to use firestore in the entire class. An example matching to the cities example from issue #1 would be:

import Swift
import Firebase
import FirebaseFirestore
import FirebaseFirestoreSwift

class CitiesViewModel: ObservableObject {
  
   let db = Firestore.firestore()
   let storage = Storage.storage()

   // ... [a lot of other stuff] ...

   private func deleteDocument(cityDocumentID: String) {
       // [START delete_document]
       db.collection("cities").document(cityDocumentID).delete() { err in
           if let err = err {
               print("Error removing document: \(err)")
           } else {
               print("Document successfully removed!")
           }
       }
    // [END delete_document]
   }

   // ... [some more stuff] ...

}

Later you just can use db in the functions you create, identical to the example function I added under issue #1 (deleteDocument()).

Best, Sebastian