解析云代码链承诺

Question

我正在尝试清理我的 Parse Cloud Code 函数以使其更易于维护。为此，我尝试使用 Promises，但无法消除错误。

这是我的代码的目的：

• 递减User1 的分数
• 向User2推送通知，说 --> User1.name要求您：操作

实际云代码（工作）：

Parse.Cloud.useMasterKey();
var action = request.object.get("action");
var from = request.object.get("from");
var to = request.object.get("to");
var reward = request.object.get("reward");

// Query 'from User' to decrement his score
var queryScore = new Parse.Query(Parse.User);
queryScore.get(from.id, {
  success: function(score)
  {
    // Decrement score of 'fromUser'.
    var newScore = score.get("score");
    newScore -= reward;
    score.set("score", newScore);

    score.save(null, {
      success: function(success)
      {
        // Score was saved.
        // Find devices associated with 'to User'
        var queryTo = new Parse.Query(Parse.User);
        queryTo.equalTo("objectId", to.id);
        var pushQueryTo = new Parse.Query(Parse.Installation);
        pushQueryTo.matchesQuery("user", queryTo);

        pushQueryTo.first({
          success: function(installation)
          {
            // Device found
            // Fetch 'from User' infos
            from.fetch({
              success: function(User) {

                // 'from User' fetched
                // Send Push to 'to User'
                var first_name = User.get("first_name");

                var preferredLanguages = installation.get("preferredLanguages");
                var alert = ""

                switch (preferredLanguages) {
                  case "fr":
                    alert = first_name + " vous demande de : " + action
                    break;
                  default:
                    alert = first_name + " is asking you to : " + action
                }

                Parse.Push.send({
                    where: pushQueryTo,
                    data: {
                      "alert": alert,
                      "badge": "Increment",
                      "content-available": "1",
                      "type": "actionAsked",
                      "sound": "default"
                    }
                  });

                  // Everything is done!
                  response.success();

              },
              error: function(error) {
                // An error occurred.
                response.error(error);
              }
            });
          },
          error: function(error)
          {
            // An error occurred.
            response.error(error);
          }
        });
      },
      error: function(error)
      {
        // An error occurred.
        response.error(error);
      }
    });

  },
  error: function(error)
  {
    // An error occurred.
    response.error(error);
  }
});

链承诺云代码（不工作）：

Parse.Cloud.useMasterKey();
var action = request.object.get("action");
var from = request.object.get("from");
var to = request.object.get("to");
var reward = request.object.get("reward");

// Query 'from User' to decrement his score
var queryScore = new Parse.Query(Parse.User);
queryScore.get(from.id).then(function(score) {

    // Decrement score of 'fromUser'.
    var newScore = score.get("score");
    newScore -= reward;
    score.set("score", newScore);

    return score.save();

}).then(function(result) {

    // Score was saved.
    // Find devices associated with 'to User'
    var queryTo = new Parse.Query(Parse.User);
    queryTo.equalTo("objectId", to.id);
    var pushQueryTo = new Parse.Query(Parse.Installation);
    pushQueryTo.matchesQuery("user", queryTo);

    return pushQueryTo.first();

}).then(function(device) {

    // Device found
    // Fetch 'from User' infos

    return from.fetch();

}).then(function(from){

    // 'from User' fetched
    // Send Push to 'to User'
    var first_name = from.get("first_name");
    var preferredLanguages = device.get("preferredLanguages");
    var alert = ""

    switch (preferredLanguages) {
        case "fr":
            alert = first_name + " vous demande de : " + action
            break;
        default:
            alert = first_name + " is asking you to : " + action
    }

    Parse.Push.send({
        where: pushQueryTo,
        data: {
            "alert": alert,
            "badge": "Increment",
            "content-available": "1",
            "type": "actionAsked",
            "sound": "default"
        }
    });

    // Everything is done!
    response.success();

},function(error) {

    // An error occurred.
    response.error(error);

});

我得到的错误：

显然我的错误与“设备”变量有关。

Answer 1

在转换为承诺时，您也取消了嵌套，导致device并且pushQueryTo不再在以后的处理程序中。使用缩进良好的代码（如问题中所示），在源代码中很容易观察到像这样的范围问题。

幸运的是，无论在何处then()处理程序返回承诺，您都可以自由地直接链接到返回该承诺的表达式，而不是添加到最外层的承诺链。

此处的修复只是通过直接链接到pushQueryTo.first()和来重新引入一些嵌套from.fetch()。

Parse.Cloud.useMasterKey();
var action = request.object.get("action");
var from = request.object.get("from");
var to = request.object.get("to");
var reward = request.object.get("reward");

var queryScore = new Parse.Query(Parse.User);
queryScore.get(from.id)
.then(function(score) {
    score.set('score', score.get('score') - reward);
    return score.save();
})
.then(function(result) {
    var queryTo = new Parse.Query(Parse.User);
    queryTo.equalTo('objectId', to.id);
    var pushQueryTo = new Parse.Query(Parse.Installation);
    pushQueryTo.matchesQuery('user', queryTo);
    return pushQueryTo.first()
    .then(function(device) {
        return from.fetch()
        .then(function(from) {
            var alert;
            switch (device.get('preferredLanguages')) {
                case 'fr': alert = from.get('first_name') + ' vous demande de : ' + action; break;
                default: alert = from.get('first_name') + ' is asking you to : ' + action;
            }
            Parse.Push.send({
                where: pushQueryTo,
                data: { 'alert': alert, 'badge': 'Increment', 'content-available': '1', 'type': 'actionAsked', 'sound': 'default' }
            });
            response.success();
        });
    });
}).catch(function(error) {
    response.error(error);
});

请注意，我说这是“一个”解决方案，而不是“那个”解决方案。换言之，存在其他方法。在 .then() 链中访问先前承诺结果的整个主题在此处进行了非常全面的讨论。