Javascript使用异步循环保存

Question

我保存了三个结果，但它们都是一样的。我遇到了异步循环问题。我该怎么摆脱这一切？

我的代码：

 var teamMatch = function(){
     var Pairingteam = [];
     var promise = Parse.Promise.as();
     var x = matchedPairingIds.length;
     while (x--) {
         var match = matchedPairingIds[x];
         var matching = function () {
             matched.set("team", {
               __type: "Pointer",
               className: "_User",
               objectId: "yCDDEWoiwM"
               });
             matched.set("Pairing", {
              __type: "Pointer",
              className: "Pairing",
              objectId: match
              });
             Pairingteam.push(matched.save());
            }
          }
          promise.then(function(){
            return Parse.Promise.when(Pairingteam);
          });
      }
     teamMatch();

Answer 1

错误是我把同班同学吊起来了。匹配需要在循环中定义。代码应该如下所示：

var teamMatch = function(){
     var Pairingteam = [];
     var promise = Parse.Promise.as();
     var x = matchedPairingIds.length;
     while (x--) {
         var matched = new Parse.Object("Matched"); //THIS IS THE MISSING PIECE
         var match = matchedPairingIds[x];
         var matching = function () {
             matched.set("team", {
               __type: "Pointer",
               className: "_User",
               objectId: "yCDDEWoiwM"
               });
             matched.set("Pairing", {
              __type: "Pointer",
              className: "Pairing",
              objectId: match
              });
             Pairingteam.push(matched.save());
            }
          }
          promise.then(function(){
            return Parse.Promise.when(Pairingteam);
          });
      }
     teamMatch();

Answer 2

问题是matched.save();是一个异步操作。很可能您的函数在所有保存完成之前返回。要克服这个问题，最好的办法就是使用承诺。在这里读一读：guide#promises

然后看看Parse JavaScript SDK and Promise Chaining和Multiple Queries Parse Javascript

将上述解决方案应用于您的问题如下：

 var partnerMatch = function() {
 var savePromises = [];  // this will collect save promises 

// Create a trivial resolved promise as a base case.
 var promise = Parse.Promise.as();
 var x = matchArray.length // x = 3
 while (x--) {
     var matched = matchArray[x];
     var matching = function() {
         matched.set("partner", {
             __type: "Pointer",
             className: "_User",
             objectId: "yCDDEWoiwM"
         });
         matched.set("match", match);
         savePromises.push(matched.save());
     }
 }

 promise.then(function(){
   // now do the saves
   return Parse.Promise.when(savePromises);
 });
 }
 partnerMatch();

Promise.When()；等待直到传递给它的所有承诺都被解析。

编辑

我不知道matched变量是从哪里来的，但是下面是更新的代码

 var teamMatch = function(){
 var Pairingteam = [];
 var promise = Parse.Promise.as();
 var x = matchedPairingIds.length;
 while (x--) {
     var match = matchedPairingIds[x];
     matched.set("team", {
       __type: "Pointer",
       className: "_User",
       objectId: "yCDDEWoiwM"
       });
     matched.set("Pairing", {
      __type: "Pointer",
      className: "Pairing",
      objectId: match
      });
     Pairingteam.push(matched.save());
     }
      promise.then(function(){
        return Parse.Promise.when(Pairingteam);
      });
  }
 teamMatch();