CODEWITHSUNDEEP
javascriptparse-platformparse-cloud-code
Charlie
Charlie

Reputation: 35

Pass a list to Parse.Promise.when but only get first element in promises chain

Hi all, I got a problem when using Parse.Promise.when in Parse Cloud Code.

In my Parse Cloud Code, I want to update the arrival time of a list of flight records which already existed in my database.

What I'm doing is pass a flight_list which is the latest flight record and iterate each record, find the responding record using Parse.Query.first and push the promises to a list and return the list to the next promise chain then function.

I expect I can get a list of result, but I only get the first query result and have no idea why. The following is my code:

// Here we start a function

Parse.Cloud.httpRequest(
    // Some HTTP request
).then(function(httpResponse) {

    // Some pre-processing...
    // flight_list is obtained here. It is a list of javascript object

    // Here start the related code
    var FlightInfo = Parse.Object.extend('FlightInfo');  // Flight object
    var promises = [];  // Promise list for next promise chain input

    // Iterate each element in flight_list
    _.each(flight_list, function(flight) {
        var query = new Parse.Query(FlightInfo);

        query.equalTo('flight_date' , flight_date);
        query.equalTo('air_carrier' , flight.air_carrier);
        query.equalTo('flight_no'   , flight.flight_no);
        query.equalTo('terminal'    , flight.terminal);
        query.equalTo('origin'      , flight.origin);

        // Push query.first promises to a list
        promises.push(query.first());
    });

    // Return promise list and flight_list for next "then" function use
    return Parse.Promise.when(promises, flight_list);

}).then(function(query_result) {
    // 1. query_result should be the promises list in the previous then function
    // 2. flight_list will be accessed using argument keyword

    // !! Only got first element from promises list in previous function
    console.log('query_result:');
    console.log(query_result);

    // No problem for flight_list. 
    for (var i = 0; i < arguments.length; i += 1) {
        console.log(i + ':' + JSON.stringify(arguments[i]));
    }

});

As the code above, I expect query_result is a list of javascript object (flight information) like: [{object1}, {object2}, {object3}, ...] But query_result is an object: {object1}. It is even not one object in a list like [{object1}].

Did I miss anything in my code? How should I modify my code to get the correct return value?

Upvotes: 2

Views: 1125

Answers (1)

Tushar Nallan
Tushar Nallan

Reputation: 784

You're getting confused with the API params. Parse.Promise.when has 2 signatures -

  1. when(promise1, promise2)
  2. when(promises) <- cant send flight_list as second param as it's not a promise.

Since you're sending the 2nd param, which isn't a promise, you're unknowingly using the 1st when. Hence the response only has 1 element corresponding to the first promise.

Solution is

// Where mFlightList is a global variable
mFlightList = flight_list;
return Parse.Promise.when(promises);

}).then(function() {
    // arguments contains the actual result of the promises passed in 'when'
    for (var i = 0; i < arguments.length; i += 1) {
        console.log(i + ':' + JSON.stringify(arguments[i]));
    }

});

Upvotes: 1

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