SwiftUI中Firestore GeoQuery匹配GeoHash却返回空文档问题

问题背景 #

将场地（Venue）数据保存到Firebase Firestore时，已通过以下代码生成并存储GeoHash（示例值：gcpvhfh0cv），且确认存储正常：

static func generateGeoHash(latitude: Double, longitude: Double) -> String {
    let location = CLLocationCoordinate2D(latitude: latitude, longitude: longitude)
    return GFUtils.geoHash(forLocation: location)
}

参考官方文档及相关方案实现queryVenuesForRegion函数，使用DispatchGroup处理异步查询：

func queryVenuesForRegion(userRegion: MKCoordinateRegion, completion: @escaping ([Venue]) -> Void) {
        
    //Get a reference to the database
    let db = Firestore.firestore()
    
    let centerCoordinate = userRegion.center
    let radiusInMeters: Double = 50 * 1000 //max(userRegion.span.latitudeDelta, userRegion.span.longitudeDelta) * 5000 // Approximate conversion, adjust as needed

    // Calculate the query bounds using GeoFire utility function
    let queryBounds = GFUtils.queryBounds(forLocation: centerCoordinate, withRadius: radiusInMeters)

    // Create a query to retrieve venues within the region
    let queries = queryBounds.map { bound -> Query in
        return db.collection("venues")
            .order(by: "geoHash")
            .start(at: [bound.startValue])
            .end(at: [bound.endValue])
    }
    
    // Create a dispatch group outside of the query loop since each iteration of the loop
        // performs an asynchronous task.
        let dispatch = DispatchGroup()
    
    var matchingDocs = [QueryDocumentSnapshot]()
    
    // Collect all the query results together in a sinlge list
    func getDocumentsCompletion(snapshot: QuerySnapshot?, error: Error?) {
        guard let documents = snapshot?.documents else {
            print("Unable to fetch snapshot data. \(String(describing: error))")
            completion([])
            dispatch.leave() // leave the dispatch group when we exit this completion
            return
        }
        

        for document in documents {
                let lat = document.data()["latitute"] as? Double ?? 0
                let lng = document.data()["longitude"] as? Double ?? 0
                let coordinates = CLLocation(latitude: lat, longitude: lng)
                let centerPoint = CLLocation(latitude: centerCoordinate.latitude, longitude: centerCoordinate.longitude)

                // We have to filter out a few false positives due to GeoHash accuracy, but
                // most will match
                let distance = GFUtils.distance(from: centerPoint, to: coordinates)
                if distance <= radiusInMeters {
                    matchingDocs.append(document)
                }
            }
        dispatch.leave() // leave the dispatch group when we exit this completion
    }
    
    // After all callbacks have executed, matchingDocs contains the result. Note that this
    // sample does not demonstrate how to wait on all callbacks to complete.
    for query in queries {
        dispatch.enter() // enter the dispatch group on each iteration
        query.getDocuments(completion: getDocumentsCompletion)
    }
        // [END fs_geo_query_hashes]
    
    var venues = [Venue]()
    
    dispatch.notify(queue: .main) {
        for document in matchingDocs {
            if let venue = try? document.data(as: Venue.self) {
                venues.append(venue)
            }
        }
    }
    
    // Call the completion handler with the parsed venues
        completion(venues)
}

调用该函数时，已确认查询区域（如伦敦市中心）与场地坐标匹配，queryBounds和queries均有数据，但documents和matchingDocs始终为空；直接获取所有文档可成功并正常显示地图标注。

排查思路 #

• 检查字段名一致性：确认Firestore文档中GeoHash的存储字段名是geoHash（注意大小写）；同时注意代码中获取纬度的字段拼写错误——代码里写的是latitute，正确应为latitude，这会导致获取的纬度值默认是0，进而距离计算错误过滤掉所有结果。
• 验证GeoHash边界范围：手动计算目标区域中心坐标的GeoHash范围，对比queryBounds返回的startValue和endValue是否包含已存储的示例GeoHash（gcpvhfh0cv），若范围不匹配，说明GFUtils.queryBounds的计算逻辑存在问题。
• 确认Firestore索引配置：Firestore对order(by: "geoHash")结合start(at:)/end(at:)的查询需要创建复合索引。进入Firestore控制台，查看是否有未创建的索引提示（查询失败时控制台会给出创建链接），确保索引已正确配置。
• 调试查询原始结果：在getDocumentsCompletion中，先打印所有返回文档的geoHash值，确认是否有文档被查询到但被距离过滤掉。若有文档返回，重点检查距离计算逻辑是否正确。
• 修复DispatchGroup执行顺序：当前代码中completion(venues)在dispatch.notify之前执行，此时venues还是空数组。需要将completion(venues)移到dispatch.notify的闭包内部，确保所有查询完成后再返回结果：

  dispatch.notify(queue: .main) {
      var venues = [Venue]()
      for document in matchingDocs {
          if let venue = try? document.data(as: Venue.self) {
              venues.append(venue)
          }
      }
      completion(venues) // 移到此处
  }
  // 移除外部的completion(venues)调用
  

• 测试单个查询：从queries中取出单个Query单独执行getDocuments，查看是否有结果，缩小问题范围是某一个查询无结果还是所有查询都无结果。
• 验证距离计算逻辑：用已知的坐标对（比如伦敦市中心坐标和场地坐标）手动计算实际距离，对比GFUtils.distance(from:to:)的返回值是否正确，若计算错误会导致合法文档被错误过滤。

内容的提问来源于stack exchange，提问作者Phil