由于Firebase查询中的大量元素而处理内存使用情况

Question

我正在编写将Firebase中的元素附加到数组以使用文本字段执行简单搜索的代码。

该方法的代码如下：

 var filteredEvents = [Event]()
var eventsArray = [Event]()
fileprivate func fetchEvents(){
    print("Fetching events....")
    //create a reference to the location in the database that you want to pull from and observe the value there
    let ref = Database.database().reference().child("events")
    // this will retur a snapshot with all the data at that location in the database and cast the results as a dictionary for later use
    ref.observe(.value, with: { (snapshot) in
        guard let dictionaries = snapshot.value as? [String: Any] else{
            return
        }
        //does the job of sorting dictionary elements by key and value
        //displaying the key and each corresponding value
        dictionaries.forEach({ (key,value) in
           // print(key, value)
            //creating an eventDictionary to store the results of previous call
            guard let eventDictionary = value as? [String: Any] else{
                return
            }
            //will cast each of the values as an Event based off my included struct
            //Make sure to create a model it is the only way to have the data in the format you want for easy access
             let events = Event(currentEventKey: key, dictionary:eventDictionary)
            // appends that to the dictionary to create the dictionary of events
            self.eventsArray.append(events)
        })
        // will sort the array elements based off the name
        self.eventsArray.sort(by: { (event1, event2) -> Bool in
            return event1.currentEventName.compare(event2.currentEventName) == .orderedAscending
        })
        // will again reload the data
        self.collectionView?.reloadData()

    }) { (err) in
        print("Failed to fetch events for search")
    }
}

我个人没有想到有可能发生很多事件的机会。我将无法将所有1000多个事件附加到字典中。那会刺痛我的记忆。无论如何，我可以让查询响应文本字段。也有人可以帮助我完成执行该操作但不会破坏我的记忆的查询行吗？

"events" : {
"CCDS" : {
  "attend:count" : 1,
  "event:date" : {
    "end:date" : "08/09/2017",
    "end:time" : "7:00 PM",
    "start:date" : "08/09/2017",
    "start:time" : "5:00 PM"
  },
  "event:description" : "Happy hour is more joyful in the summer thanks to Center City District Sips, which offers discounted drinks and appetizers every Wednesday evening.  Catch up with old friends and make a few new ones as Center City’s best bars and restaurants host the summer’s happiest hour every Wednesday from 5-7 p.m.  Enjoy $5 cocktails, $4 wine, $3 beers and half-price appetizers at dozens and dozens of bars and restaurants.",
  "event:imageURL" :someURL",
  "event:location" : {
    "event:city" : "Philadelphia",
    "event:state" : "PA",
    "event:street:address" : "660 Chestnut St",
    "event:zip" : 19106
  },
  "event:name" : "Center City District Sips"
},
"MIA" : {
  "attend:count" : 1,
  "event:date" : {
    "end:date" : "09/03/2017",
    "end:time" : "7:00 PM",
    "start:date" : "09/02/2017",
    "start:time" : "12:00 PM"
  },
  "event:description" : "Budweiser Made in America Festival is an annual music festival held in Philadelphia and formerly simultaneously held in Los Angeles.Sponsored by Anheuser–Busch and produced by Live Nation, the event features several stages that continuously host live music from a wide range of genres including hip hop, rock, pop, R&B, and EDM.",
  "event:imageURL" : "someURL",
  "event:location" : {
    "event:city" : "Philadelphia",
    "event:state" : "PA",
    "event:street:address" : "Ben Franklin Parkway",
    "event:zip" : 19130
  },
  "event:name" : "Made In America"
}
  },

例如，我想提取有关使用查询搜索的事件的所有信息。因此，如果我开始输入“美国制造”，它将从“事件”标签中提取有关该事件的所有相关信息

这是我目前拥有的

fileprivate func fetchEvents(searchString: String){
    print("Fetching events....")
    //create a reference to the location in the database that you want to pull from and observe the value there
    let ref = Database.database().reference().child("events")
    // this will retur a snapshot with all the data at that location in the database and cast the results as a dictionary for later use
  let query = ref.queryOrdered(byChild: "event:name").queryEqual(toValue: searchString)
    print(query)
    query.observeSingleEvent(of: .value, with: { (snapshot) in
        guard let dictionary = snapshot.value as? [String: Any] else{
            print(snapshot.value)
            return
        }
        print(snapshot.value)
    }) { (err) in
        print("Failed to fetch event data", err)
    }

}

返回此

(/events { ep = Made In America; i = "event:name"; sp = Made In America; })

Answer 1

看来问题是

"How can I query for a value contained in a child node?"

给出与原始结构相似的结构

"events" : {
  "CCDS" : {
    "attend:count" : 1,
    "event:imageURL" :"someURL",
    "event:name" : "Center City District Sips"
  "MIA" : {
    "attend:count" : 1,
    "event:imageURL" : "someURL",
    "event:name" : "Made In America"

Firebase查询将返回您想要的节点。

如果用户键入 “美国制造” 并点击搜索按钮，则查询将返回快照中的该节点。

let searchString = "Made In America"
let ref = self.ref.child("events")
let query = ref.queryOrdered(byChild: "event:name").queryEqualTo(searchString)
query.observeSingleEvent(of: .value, with: { (snapshot) in
    for child in snapshot.children {
        let snap = child as! DataSnapshot
        let eventDict = snap.value as! [String: Any]
        let attendCount = eventDict["attend:count"] as! String
        let url = eventDict["event:imageURL"} as! String
    }
})

如果您想进行部分字符串匹配，则用户可以只输入几个字符，例如 Made 代码类似，但是您需要让firebase返回所有以Made开头的匹配项…

查询看起来像这样

let startString = "Made"
let endString = "Made" + "\\uf8ff"
let query = ref.queryOrdered(byChild: "event:name")
                        .queryStarting(atValue: startString)
                        .queryEnding(atValue: endString")

“ \ uf8ff”是Unicode中很高代码级别的字符-因为它包含所有前面的字符。

但是，“即时”查询会创建无响应或反应迟缓的UI，因此不建议这样做。

一种替代方法是创建一个单独的节点，该节点包含的信息要少得多，并包含用户要搜索的元素以及对事件节点的引用。

所以包含所有数据的主节点看起来像这样

"events" : {
  "-uyuh8s8j8jsdas" : {
    "event": "CCDS"
    "attend:count" : 1,
    "event:imageURL" : "someURL",
  "-y88jsijsijjids" : {
    "event": "MIA"
    "attend:count" : 1,
    "event:imageURL" : "someURL",

一个“较小”的节点看起来像这样

   events_for_searching
       -uyuh8s8j8jsdas
         event:name: "Center City District Sips"
       -y88jsijsijjids
         event:name: "Made In America"

这样，您可以将来自events_for_searching的所有节点加载到一个数组中（然后根据用户类型过滤该数组），这将使UI非常敏感，并且当用户选择名称时，您可以使用该节点中的键作为参考，以便通过observeSingleEvent函数从事件节点加载数据。

编辑

为了回应评论，我想在代码中添加更多细节。

这是我的结构

  "events" : {
    "event_0" : {
      "event:name" : "An Event"
    },
    "event_1" : {
      "event:name" : "Made In America"
    }
  },

以及用于查询事件的代码：名称：美国制造

let searchString = "Made In America"
let ref = self.ref.child("events")
let query = ref.queryOrdered(byChild: "event:name").queryEqual(toValue: searchString)

query.observeSingleEvent(of: .value, with: { (snapshot) in
    guard let dictionary = snapshot.value as? [String: Any] else{
        print(snapshot.value)
        return
    }
    print(snapshot.value)
}) { (err) in
    print("Failed to fetch event data", err)
}

和输出

Optional({
    "event_1" =     {
        "event:name" = "Made In America";
    };
})