EXPO和Firebase实时数据库-在写入数据库之前读取值并确认不存在特定值

问题描述

我有一个功能正常的Reaction Native EXPO应用程序，它与我的Firebase实时数据库交互。简而言之，我在试图找到一种方法来检查所有子值以查看是否存在某个值，然后将该值(再次)作为新记录写入数据库，这让我感到困惑。

我过去一直从我的App.js中的世博会推送通知API获取&Quot；ExponentPushToken&Quot；，然后在从世博会推送通知API注册推送通知的相同函数中使用以下代码立即向我的Firebase实时数据库写入新记录：

      const token = (await Notifications.getExpoPushTokenAsync()).data;
      console.log(token);
      var userListRef = firebase.database().ref("users/push_token");
      var newUserRef = userListRef.push();
      newUserRef.set(token);

我还有以下代码读取数据库并将正确的信息记录到控制台，以便能够将所有输出值与前面提到的"；内标识&Quot；值进行比较：

var userListRef = firebase.database().ref("users/push_token");
  userListRef.on("value", function (snapshot) {
    snapshot.forEach(function (child) {
      console.log(child.val());
    });
  });

      const token = (await Notifications.getExpoPushTokenAsync()).data;
      console.log(token);
      var userListRef = firebase.database().ref("users/push_token");
      userListRef.once("value", function (snapshot) {
        snapshot.forEach(function (child) {
          createPushTokenArray(child.val());
          myTokenHandler(token);
        });
      });

  var allPushTokens = [];
  async function createPushTokenArray(dbState) {
    allPushTokens.push(dbState);
    return;
  }

  async function myTokenHandler(myToken) {
    await createPushTokenArray();
    var checkForValue = allPushTokens.includes(myToken);
    if (checkForValue === true) {
      return console.log("Push Token already stored in database.");
    } else {
      var userListRef = firebase.database().ref("users/push_token");
      var newUserRef = userListRef.push();
      var writeNewToken = newUserRef.set(myToken);
      writeNewToken;
      return console.log("New Push Token stored in database.");
    }
  }

我多次尝试在这一切中取得任何进展，但都是徒劳的。作为参考，下面是db结构(JSON格式)：

{
  "users" : {
    "push_token" : {
      "key or name" : "value",
      "-Maer1EuNpR24LdhxmIl" : "ExponentPushToken[xxxxxxxxxxxxxxxxxxxxxx]",
    }
  }
}

推荐答案

实际上我自己就能弄清楚，对任何感兴趣的人来说。这可能不是最干净的方法，但结果正好产生了我需要的东西。

而不是运行不可停止的forEach()循环，我只是获取整个数据库，然后定义它，并只提取值。

请参阅下面的代码，它可以有效地检查数据库中的所有值是否都包含我们的特定值。

      const token = (await Notifications.getExpoPushTokenAsync()).data;
      console.log(token);
      //---The above sits inside of a function. It is Expo's code for expo-notifications api----///
      var userListRef = firebase.database().ref("users/push_token");
      userListRef.once("value", function (snapshot) {
        createPushTokenArray(snapshot.val());
        myTokenHandler(token);
      });
      //---More code here to close function(s) and complete expo-notificaions api integration for Push Notifications---///
  var allPushTokens = [];
  function createPushTokenArray(dbState) {
    const defineDb = new Object(dbState);
    const newState = Object.values(defineDb);
    allPushTokens.push(newState);
  }
  async function myTokenHandler(myToken) {
    await createPushTokenArray();
    const cleanSearch = allPushTokens.values();
    for (const allData of cleanSearch) {
      console.log(allData);
      var checkForValue = allData.includes(myToken);
      if (checkForValue == true) {
        console.log("Push Token already stored in database.");
        break;
      } else {
        var userListRef = firebase.database().ref("users/push_token");
        var newUserRef = userListRef.push();
        var writeNewToken = newUserRef.set(myToken);
        writeNewToken;
        console.log("New Push Token stored in database.");
        break;
      }
    }
  }

其工作原理如下：

      var userListRef = firebase.database().ref("users/push_token");
      userListRef.once("value", function (snapshot) {
        createPushTokenArray(snapshot.val());
        myTokenHandler(token);
      });

  var allPushTokens = [];
  function createPushTokenArray(dbState) {
    const defineDb = new Object(dbState);
    const newState = Object.values(defineDb);
    allPushTokens.push(newState);
  }

  async function myTokenHandler(myToken) {
    await createPushTokenArray();
    const cleanSearch = allPushTokens.values();
    for (const allData of cleanSearch) {
      console.log(allData);
      var checkForValue = allData.includes(myToken);
      if (checkForValue == true) {
        console.log("Push Token already stored in database.");
        break;
      } else {
        var userListRef = firebase.database().ref("users/push_token");
        var newUserRef = userListRef.push();
        var writeNewToken = newUserRef.set(myToken);
        writeNewToken;
        console.log("New Push Token stored in database.");
        break;
      }
    }
  }