Swift：将单个文档映射到 Firebase Firestore 中的结构

Question

I'm try to map a single Firestore document to a @Published var of my ObservableObject repository class.

The struct that the document is mapped to obeys the codable protocol, so this should be straight forward, but I am missing something somewhere, as the document data is not showing in my UI.

class Repository: ObservableObject {
  
  let db = Firestore.firestore()
  
  @Published var documentData: DocumentData?
  
  func getDocumentDataById(id: String) {
    
    db.collection("documentData").document(id)
      .addSnapshotListener { documentSnapshot, error in
        print("fetching")
        if let documentSnapshot = documentSnapshot, documentSnapshot.exists {
          do {
            print("document exists")
            self.documentData = try documentSnapshot.data(as: DocumentData.self)
          } catch {
            print(error)
          }
        }
      }
  }
}

The logs show "fetching", but never progress to show either "document exists" or the error.

What am I doing wrong?

Answer 1

When you use addSnapshotListener to listen to real-time updates, you're attaching a listener that is called for any change that occurs in your database. As a result, this happens even when your app is ended, which is why detaching the listeners before the activity is killed is required.

Here is an example of how you can update your current code:

db.collection(documentData).document(id)
    .addSnapshotListener { documentSnapshot, error in
      guard let document = documentSnapshot else {
        print("Error fetching document: \(error!)")
        return
      } 
      guard let data = document.data() else {
        print("Document data was empty.")
        return
      }
      print("Current data: \(data)")
    }