从另一个“getDocument”查询中的“getDocument”查询中检索数据

Question

我的代码从 Firestore 检索数据时遇到问题。

我的代码中有 2 个类：Exercise 和 Tag。 我的 FirestoreDatabase 中有 2 个集合：练习和标签

我需要从“练习”集合中获取所有“练习”文档。每个“练习”文档都有一个名为“标签”的字段，它是一个字符串数组。数组的每个字符串都包含引用“tag”在“tags”集合中的文档的“id”。因此，在“tags”集合中查询这个 id，使我能够获得正确的“tag”文档并访问其所有数据。这正是我想要在我的代码中做的。

我需要将所有练习添加到一个练习对象中，为此我必须在另一个 getDocument 查询中使用 getDocument 查询，以便从“标签”集合中获取练习的“标签”

这是我的课程标签和练习：

class Tag {  
var id: String?
var type: String?
var description: String?

init(id: String, type: String, description: String) {
    self.id = id
    self.type = type
    self.description = description
  }
}

class Exercise {
   let id: String?
   let group: String?
   let tags: [Tag]
   let title : String!

   init(id: String, group: String, tags: [Tag], title: String){  
    self.id = id
    self.group = group
    self.tags = tags
    self.title = title   
  }

}

这是我从 Firestore 数据库中获取“练习”的代码：

func fetchExercises(completion: @escaping ([Exercise]) -> ()) {

    let exercisesRef = Firestore.firestore().collection("exercises")

    exercisesRef.getDocuments() { (querySnapshot, err) in

        var exercisesArray = [Exercise]()

        if let err = err {
            print("Error getting documents: \(err)")
        } else {
            for document in querySnapshot!.documents {
                //print("\(document.documentID) => \(document.data())")

                let myData = document.data()
                let exercise_ID = document.documentID
                let exercise_group = myData["Group"] as! String
                let tagsArray = myData["Tags"] as! [String]

                var exercise_tags: [Tag] = [Tag]()

                for tag in tagsArray {
                    let tagID: String = tag
                    fetchTagfromID(tagID: tagID) { (tag: Tag) in
                        exercise_tags.append(tag)
                    }
                }

                let exercise_title = myData["Title"] as! String                 

                exercisesArray.append(Exercise(id: exercise_ID,
                                               group: exercise_group,
                                               tags: exercise_tags,
                                               title: exercise_title,
                ))
            }
            DispatchQueue.main.async{
               print("EXERCISE FETCH HAS FINIS")
                completion(exercisesArray)
            }
        }
    }
}


func fetchTagfromID(tagID: String, completion: @escaping (Tag) -> ()) {


let tagRef = Firestore.firestore().collection("tags").document(tagID)

tagRef.getDocument() { (document, err) in

    if let err = err {
        print("Error getting documents: \(err)")
    } else {

        let myData = document?.data()

        let tagDescription: String = myData!["description"] as! String
        let tagType: String =  myData!["type"] as! String
        let tag: Tag = Tag(id: tagID, type: tagType, description: 
tagDescription)


        DispatchQueue.main.async{
            print("TAGS FETCH HAS FINISHED")
            completion(tag)
        }
    }
  }
}

我的问题在于执行时间（队列）代码。

我需要先填写“exercise_tags”（辅助 getDocument 查询），然后继续并完成 fetchExercise（主要 getDocument 查询），但 Firestore 不允许（或不知道如何）这样做。代码首先完成主 getDocument 查询 (fetChExercises)，然后返回完成辅助 getDocument 查询 (fetchTagfromID)。

总之，我需要在运行时得到这个日志：

TAGS FETCH HAS FINISHED
EXERCISES FETCH HAS FINISHED

现在我的情况正好相反。

你们知道如何解决这个问题吗？也许改变调度队列......

我现在如何分两步解决这个问题，但优雅的解决方案是一步完成所有事情。这就是 fetchExercises。

谢谢！

Answer 1

所以你需要做的是获取一个练习的所有标签，然后获取另一个练习。毕竟 fetch 调用完成处理程序来更新 UI。我对代码做了一些更改，您可以检查一下。

   var exercisesArray = [Exercise]()
   var listFromFetchExercise = []()  //it will contain all object of array 
   querySnapshot!.documents. set DataType according to that.
   var completion_exercises_Listner: () -> ()

   func fetchExercises(completion: @escaping ([Exercise]) -> ()) {

   let exercisesRef = Firestore.firestore().collection("exercises")

exercisesRef.getDocuments() { (querySnapshot, err) in

    if let err = err {
        print("Error getting documents: \(err)")
    } else {

        listFromFetchExercise = querySnapshot!.documents
        fetchAllExercise()

        DispatchQueue.main.async{
           print("EXERCISE FETCH HAS FINIS")
            completion(exercisesArray)
        }
    }
}
}

func fetchAllExercise(completion: @escaping ([Exercise]) -> ()){

fetchExercise()
completion_exercises_Listner = {
    completion(exercisesArray);
}

}

func fetchExercise(index:Int = 0) {

  let document = listFromFetchExercise[index]

  let myData = document.data()
  let exercise_ID = document.documentID
  let exercise_group = myData["Group"] as! String
  let tagsArray = myData["Tags"] as! [String]

  var exercise_tags: [Tag] = [Tag]()

  fetchTagsFromIDS(tagsArray) { (tag: [Tag]) in
  exercise_tags.append(contentsOf: tag)

  let exercise_title = myData["Title"] as! String                 

  exercisesArray.append(Exercise(id: exercise_ID,
                               group: exercise_group,
                               tags: exercise_tags,
                               title: exercise_title,

   DispatchQueue.main.async{
      exercisesArray.append(tag)
      if (index + 1) < exercisesArray.count {
        fetchExercise(index+1,)
      }else{
        //Done
        completion_exercises_Listner()
      }

  }
   ))

  }



 var listofTags = [String]()
 var resultofTags = [Tag]()

   func fetchTagsFromIDS(tagIDS:[String],completion: @escaping (_ tags:[ 
 String]) -> ()){

listofTags = tagIDS;
fetchTagfromID() //Start With first tag

completionListner = {
    completion(resultofTags);
}

}

var completionListner: () -> ()

func fetchTagfromID(index:Int = 0) {

 let tagRef = Firestore.firestore().collection("tags").document(tagID)

 tagRef.getDocument() { (document, err) in

if let err = err {
    print("Error getting documents: \(err)")
} else {

    let myData = document?.data()

    let tagDescription: String = myData!["description"] as! String
    let tagType: String =  myData!["type"] as! String
    let tag: Tag = Tag(id: tagID, type: tagType, description: 
   tagDescription)


    DispatchQueue.main.async{
        print("TAGS FETCH HAS FINISHED")
        resultofTags.append(tag)
        if (index + 1) < listofTags.count {
          fetchTagfromID(index+1,)
        }else{
          //Done
          completionListner()
        }
        //completion(tag)
    }
}
} }