Swift Firestore 中带有文档参考的嵌套结构

Question

I have a Book model looking like this:

struct Book: Identifiable {
    var id = UUID().uuidString
    var text: String
    var styleReference: DocumentReference
    
    var style: BookStyle //not in the Firestore Document
}

with the style looking like this:

struct BookStyle: Identifiable {
    var id = UUID().uuidString
    var imageUrlString: String
    var fontString: String
}

This is what my Firestore Book model looks like:

I can fetch the Books like this:

func fetchData() {
  db.collection("books").addSnapshotListener { (querySnapshot, error) in
    guard let documents = querySnapshot?.documents else { return }
      
    self.books = documents.compactMap { queryDocumentSnapshot -> Book? in
      return try? queryDocumentSnapshot.data(as: Book.self)
    }
  }
}

My problem now is: Where should I get the BookStyle Data? I have the reference to the document but I don't know where to fetch and assign it.

Answer 1

you could try something like this (totally untested), with var style: BookStyle? and a loop over the books:

    func fetchData() {
        db.collection("books").addSnapshotListener { (querySnapshot, error) in
            guard let documents = querySnapshot?.documents else { return }
            
            self.books = documents.compactMap { queryDocumentSnapshot -> Book? in
                return try? queryDocumentSnapshot.data(as: Book.self)
            }
            // -- here
            for i in self.books.indices {
                db.document(self.books[i].styleReference).getDocument { (snapshot, error) in
                    let bookStyle = snapshot.compactMap { queryDocumentSnapshot -> BookStyle? in
                        return try? queryDocumentSnapshot.data(as: BookStyle.self)
                    }
                    self.books[i].style = bookStyle
                }
            }
        }
    } 
}

struct Book: Identifiable {
    let id = UUID().uuidString
    var text: String
    var styleReference: DocumentReference
    var style: BookStyle? // <-- here optional
}

struct BookStyle: Identifiable {
    let id = UUID().uuidString
    var imageUrlString: String
    var fontString: String
}