Question

我想通过节点js将一些数据添加到firebase的项目列表中，但是我不知道如何检查更新过程是否失败。这是我的工具：

// set data to json 
let servicesJson = {
    "car_services": [services],
    "car_services_status": 1
}
// add car service to province
let provinceIdNumber = parseInt(provinceId, 10);
var areaRef = db.ref("areas")
areaRef.orderByChild('province_id').equalTo(provinceIdNumber).once('value', function (areaSnapshots) {
    if (areaSnapshots.val() != null) {
        var result = true 
        areaSnapshots.forEach (function (child) {
            let currentTime = new Date().toISOString();
            servicesJson.last_updated = currentTime
            child.ref.update(servicesJson, function (error) {
                if (error) {
                    console.log("*** error ***")
                    result = false
                } else {
                    console.log("*** success ***")
                    result = true
                }
            }) 
        });
        console.log("*** finished ***")
        res.send({ 'success': result });
    } else {
        res.send({ 'success': false, 'error_code': 'CSTP05', 'error_msg': 'Cant find any area of province to update car service' });
    }
});

这是日志：

*** finished ***
*** success ***
*** success ***
*** success ***
*** success ***

如何等待直到循环结束然后返回结果？

Answer 1

Use Promise

// set data to json
let servicesJson = {
  car_services: [services],
  car_services_status: 1
};
// add car service to province
let provinceIdNumber = parseInt(provinceId, 10);
var areaRef = db.ref("areas");
const updatePromise = new Promise((resolve, reject) => {
  const changedCount = 0;
  areaRef
    .orderByChild("province_id")
    .equalTo(provinceIdNumber)
    .once("value", function(areaSnapshots) {
      if (areaSnapshots.val() != null) {
        areaSnapshots.forEach(function(child) {
          let currentTime = new Date().toISOString();
          servicesJson.last_updated = currentTime;
          child.ref.update(servicesJson, function(error) {
            if (error) {
              changedCount++;
              console.log("*** error ***");
            } else {
              changedCount++;
              console.log("*** success ***");
            }
          });

          if (areaSnapshots.length === changedCount) {
            console.log("*** finished ***");
            resolve({ success: true });
          }
        });
      } else {
        reject({
          success: false,
          error_code: "CSTP05",
          error_msg: "Cant find any area of province to update car service"
        });
      }
    });
});

updatePromise
  .then(data => {
    res.send(data);
  })
  .catch(error => {
    res.send(error);
  });

Answer 2

感谢HNQ的回答，这是有效的代码：

var updatePromise = new Promise((resolve, reject) => {
    var changedCount = 0;
    var isError = false;
    areaRef
        .orderByChild("province_id")
        .equalTo(provinceIdNumber)
        .once("value", function(areaSnapshots) {
            if (areaSnapshots.val() != null) {
                areaSnapshots.forEach(function(child) {
                    let currentTime = new Date().toISOString();
                    servicesJson.last_updated = currentTime;
                    child.ref.update(servicesJson, function(error) {
                        if (error) {
                            isError = true;
                            console.log("*** error ***");
                        } else {
                            console.log("*** success ***");
                        }
                        changedCount++;
                        if (areaSnapshots.numChildren() === changedCount) {
                            console.log("*** finished ***");
                            if (isError) {
                                resolve({ success: false, error_code: 'CSTP05', error_msg: 'Failed to update all elements' });
                            } else {
                                resolve({ success: true });
                            }
                        } 
                    });
                });
            } else {
                reject({
                    success: false,
                    error_code: 'CSTP06',
                    error_msg: 'Cant find any area of province to update car service'
                });
            }
    });
});

updatePromise
    .then(data => {
        res.send(data);
    })
    .catch(error => {
        res.send(error);
    });

我添加了一个用于检测错误的标志。如果一切正常，结果将如下所示：

*** success ***
*** success ***
*** success ***
*** success ***
*** finished ***

通过Node JS将数据更新到Firebase项列表中时检查更新结果

2 个答案: