Return Pase.Query.each() 中的承诺无效

Question

在云代码后台作业中，我有一种方法可以从 API:

中检索信息

  var getUserPageView=function(userid){
    var promise=new Parse.Promise();
    Parse.Cloud.httpRequest({
        url: 'http://apiip.ch/api.php?date='+
        formatDate(new Date())
    }).then(function(httpResponse) {
        // success
        var text=httpResponse.text;
        var obj=JSON.parse(text);
        promise.resolve(parseInt(obj[0][1]));
    },function(httpResponse) {
        // error
        console.error('Request failed with response code ' + httpResponse.status);
        promise.reject();
    });
    return promise;
};

对于所有用户，我必须调用 API 来检索有关某个特定用户的信息。根据 specification of the "each()" function:

If the callback returns a promise, the iteration will not continue until that promise has been fulfilled.

我return一个承诺，会在APIreturn结果时实现。

query=new Parse.Query(Parse.User);
query.each(function(user){
    var promise=Parse.Promise().as();
    promise=promise.then(function(){
        getUserPageView(234).then(function(result){
            console.log("User page view:"+ result);
            //process user with API information
            promise.resolve("a");
        },function(){
            console.log("error");
        });
    });

    console.log("user processed");
    return promise;
}).then(function(){
    status.success("Credti update successfull.");
}, function(error){
    status.error("Uh oh, something went wrong.");
});

问题是从未调用 getUserPageView()。或者更准确地说，我认为 "each ()" 函数不会等待承诺实现。这可能是什么问题？

Answer 1

对于初学者来说，Parse.Cloud.httpRequest已经给出了一个承诺，不需要包装它：

var getUserPageView=function(userid){   // not sure why userid is required, it is not used anywhere.
    return Parse.Cloud.httpRequest({
        url: 'http://apiip.ch/api.php?date='+ formatDate(new Date())
    }).then(function(httpResponse) {    // success            
        var text=httpResponse.text;
        var obj=JSON.parse(text);
        return parseInt(obj[0][1]);
    },function(httpResponse) {  // error            
        console.error('Request failed with response code ' + httpResponse.status);
        throw httpResponse;
    });
};

至于query.each()我不是很确定，只是瞎戳一下：

query=new Parse.Query(Parse.User);
query.each(function(user){
    return getUserPageView(234).then(function(result){
        console.log("User page view:"+ result);  //process user with API information
    },function(){
        console.log("error");
    });        
}).then(function(){
    status.success("Credti update successfull.");
}, function(error){
    status.error("Uh oh, something went wrong.");
});

Answer 2

@mido22对第一种方法完全正确。只是 return 承诺 return 由 httpRequest 编辑。重复一下，修正 his/her 修正一点：

var getUserPageView=function(userid){
  return Parse.Cloud.httpRequest({
      url: 'http://apiip.ch/api.php?date='+
      formatDate(new Date())
  }).then(function(httpResponse) {
      // success
      var text=httpResponse.text;
      var obj=JSON.parse(text);
      return parseInt(obj[0][1]);
  },function(httpResponse) {
      // error
      console.error('Request failed with response code ' + httpResponse.status);
      return httpResponse;
  });
};

关于第二种方法，缺少的（至少）是来自内部承诺的 return 值。 Parse.Promise.when 使逻辑更清晰，imo，接受一系列承诺并在所有承诺都实现时实现...

// very handy for iteration and much more
var _ = require('underscore');

query=new Parse.Query(Parse.User);
query.limit(4);  // start out with a small number to make sure it works (all users will eventually run afoul of resource limits)
query.find().then(function(users){
    var promises = _.map(users, function(user) {
        return getUserPageView(234);
    });
    return Parse.Promise.when(promises);
}).then(function(){
    status.success(_.toArray(arguments));  // when() returns an array of results for each input promise, these are in var args of the success function
}, function(error){
    status.error(error);
});

Return Pase.Query.each() 中的承诺无效

Return a promise in Pase.Query.each() don't work

javascript

promise

parse-platform

parse-cloud-code