如何在 swiftui + firebase 应用程序中按城市过滤

我有一个使用 firebase 的 swiftui 应用程序。我想在向用户发布帖子时按城市进行过滤。为此，我将城市参数添加到 firebase 集合中。然后我想使用 whereField 向用户显示，但由于某种原因什么也没有发生。这是我的代码：

    struct ReusablePostViewContentView: View {
    
    var cities = ["Москва", "Волгоград", "Пермь"]
    
    @State private var selectedCity: String = "Москва"
    
    @Binding var posts: [Post]
    
    @State private var isFetching: Bool = true
    
    @State private var paginationDoc: QueryDocumentSnapshot?
    
    var body: some View {
    
    Picker("Выберите город", selection: $selectedCity) {
                    
                    ForEach(cities, id: \.self) {
    
                        Text($0)
                    }
                }

         ScrollView(.vertical, showsIndicators: false) {
            LazyVStack {
                if isFetching {
                    ProgressView()
                        .padding(.top, 30)
                } else {
                    if posts.isEmpty {
                        Text("Записи отсутствуют")
                            .font(.caption)
                            .foregroundColor(.gray)
                            .padding(.top, 30)
                    } else {
                        Posts()
                    }
                }
            }
            .padding(15)
        }
        .refreshable {
         
            isFetching = true
            posts = []
            paginationDoc = nil
            await fetchPosts()
        }
        .task {
            guard posts.isEmpty else {return}
            await fetchPosts()
        }
        }

    }

func Posts() -> some View {
        ForEach (posts) { post in
        
            PostCardViewContentViewFish(post: post) { updatedPost in
                if let index = posts.firstIndex(where: { post in
                    post.id == updatedPost.id
                }) {
                    posts[index].likedIDs = updatedPost.likedIDs
                    posts[index].dislikedIDs = updatedPost.dislikedIDs
                }
            } onDelete: {
                withAnimation(.easeInOut(duration: 0.25)) {
                    posts.removeAll {post.id == $0.id}
                }
            }
            .onAppear {
                if post.id == posts.last?.id && paginationDoc != nil {
                    Task {await fetchPosts()}
                 
                }
            }
            
            Divider()
                .padding(.horizontal, -15)

        }
    }
    
    func fetchPosts() async {
            do {
                var query: Query!
                if let paginationDoc {
                    query = Firestore.firestore().collection("Posts")
                        .whereField("yourCity", isEqualTo: selectedCity)
                        .order(by: "upPostPlusDayValueCount", descending: true)
                        .start(afterDocument: paginationDoc)
                        .limit(to: 5)
                } else {
                    query = Firestore.firestore().collection("Posts")
                        .whereField("yourCity", isEqualTo: selectedCity)
                        .order(by: "upPostPlusDayValueCount", descending: true)
                        .limit(to: 5)
                }
                
                let docs = try await query.getDocuments()
                let fetchedPosts = docs.documents.compactMap { doc -> Post? in
                    try? doc.data(as: Post.self)
                }
                await MainActor.run(body: {
                    posts.append(contentsOf: fetchedPosts) 
                    
                    paginationDoc = docs.documents.last
                  
                    isFetching = false
                })
            } catch {
                print(error.localizedDescription)
            }
        }
    }