JAVASCRIPT 无法分配从 FIRESTORE 获得的变量 - 已解决：嵌套承诺很少答案

【问题标题】：JAVASCRIPT unable to assign variables got from FIRESTORE - solved: few nested promisesJAVASCRIPT 无法分配从 FIRESTORE 获得的变量 - 已解决：嵌套承诺很少
【发布时间】：2020-06-12 10:07:04
【问题描述】：

Firestore 新手。试图尽可能清楚。无法分配从 fisetore DB 接收到的属性，在js中找不到答案。

建立一个问答论坛，有 3 个集合：用户、消息、查询。尝试添加查询（在创建 msg 和用户的有效文档并获得他们的 doc id 之后）。打印到控制台时，工作正常但不更新数据库

当遇到与数字相同的问题时，尝试使用 parseInt 进行换行并且它有效，但 parseString 似乎不存在。还尝试只声明变量而不用“”，但随后出现错误。

function DBaddNewQuery2(userID, firstMsgId) {
  let creatorFirstName =" ";
  let creatorLastName=" " ;
  let firstMsgText =" ";

  // get the user's first and last name
  db.collection("users").doc(userID).get().then(function(doc) {
    creatorFirstName = doc.data().firstName;
    creatorLastName= doc.data().lastName;
    console.log("creatorFirstName is ",creatorFirstName); // prints the right data!
    }).catch(function(error) {
    console.log("Error getting first and last name for user in addquery2:", error);
  });

  // get msg text
  db.collection("message").doc(firstMsgId).get().then(function(doc) {
    firstMsgText = doc.data().msgText;
    console.log("msg text is ",firstMsgText); // prints the right data!
    }).catch(function(error) {
    console.log("Error getting document:", error);
  });

  // generate query id
  let queryId = create_UUID();

  db.collection("query").doc(queryId).set({

    'creatorFirstName': creatorFirstName, //update db as " "
    'creatorLastName': creatorLastName,
    'firstMsgText': firstMsgText,

  }).then(function () {
    console.log("setDocument: query Document successfully written!, query id: ", queryId);
  })
    .catch(function (error) {
      console.error("setDocument: Error writing document: ", error);
    });

}

【问题讨论】：

你是否试图连续运行一堆异步函数，而后续函数依赖于之前函数的数据？
是的，如果不清楚，我很抱歉

标签： javascript database google-cloud-firestore

【解决方案1】：

1- async/await 可以在这里做点什么


    async function DBaddNewQuery2(userID, firstMsgId) {
      let creatorFirstName = ' ';
      let creatorLastName = ' ';
      let firstMsgText = ' ';

      // get the user's first and last name
      let userRef = await db
        .collection('users')
        .doc(userID)
        .get();

      creatorFirstName = userRef.data().firstName;
      creatorLastName = userRef.data().lastName;
      // get msg text
      let messageRef = await db
        .collection('message')
        .doc(firstMsgId)
        .get();

      firstMsgText = messageRef.data().msgText;

      // generate query id
      let queryId = create_UUID();

      db.collection('query')
        .doc(queryId)
        .set({
          creatorFirstName: creatorFirstName, //update db as " "
          creatorLastName: creatorLastName,
          firstMsgText: firstMsgText,
        })
        .then(function() {
          console.log(
            'setDocument: query Document successfully written!, query id: ',
            queryId,
          );
        })
        .catch(function(error) {
          console.error('setDocument: Error writing document: ', error);
        });
    }

2- 嵌套结构

function DBaddNewQuery2(userID, firstMsgId) {
  let creatorFirstName = ' ';
  let creatorLastName = ' ';
  let firstMsgText = ' ';

  // get the user's first and last name
  db.collection('users')
    .doc(userID)
    .get()
    .then(function(doc1) {
      creatorFirstName = doc1.data().firstName;
      creatorLastName = doc1.data().lastName;
      console.log('creatorFirstName is ', creatorFirstName); // prints the right data!

      // get msg text
      db.collection('message')
        .doc(firstMsgId)
        .get()
        .then(function(doc2) {
          firstMsgText = doc2.data().msgText;
          console.log('msg text is ', firstMsgText); // prints the right data!

          // generate query id
          let queryId = create_UUID();

          db.collection('query')
            .doc(queryId)
            .set({
              creatorFirstName: creatorFirstName, //update db as " "
              creatorLastName: creatorLastName,
              firstMsgText: firstMsgText,
            })
            .then(function() {
              console.log(
                'setDocument: query Document successfully written!, query id: ',
                queryId,
              );
            })
            .catch(function(error) {
              console.error('setDocument: Error writing document: ', error);
            });
        })
        .catch(function(error) {
          console.log('Error getting document:', error);
        });
    })
    .catch(function(error) {
      console.log(
        'Error getting first and last name for user in addquery2:',
        error,
      );
    });
}

【讨论】：

【解决方案2】：

这个解决方案对我有用，不仅像 @MUHAMMADILYAS 建议的那样嵌套，而且还使用 Promise.all

谢谢！

function DBaddNewQuery(userID, firstMsgId) {

  let creatorFirstName = " "; let creatorLastName = " "; let firstMsgText = " ";
  // generate query id
  let queryId = create_UUID();

  var userRef = db.collection("users").doc(userID);
  const promise1 = userRef.get();
  const promise2 = db.collection("message").doc(firstMsgId).get();
  Promise.all([promise1, promise2]).then((values) => {
    doc1 = values[0];
    doc2 = values[1];
    creatorFirstName = doc1.data().firstName;
    creatorLastName = doc1.data().lastName;
    firstMsgText = doc2.data().msgText;

    db.collection("query").doc(queryId).set({  // CREATE QUERY:

      'creatorFirstName': creatorFirstName, 
      'creatorLastName': creatorLastName,  
      'firstMsgText': firstMsgText,  
    }).then(function () {
      console.log("setDocument: query Document successfully written!");
    })
      .catch(function (error) {
        console.error("setDocument: Error writing document: ", error);
    });

  });

  return queryId;
}

【讨论】：