在云代码中解析查询后保留对象

Question

I am working on writing some Parse Cloud Code that pulls JSON from a third party API. I would like to modify it, check and see if it already exists and if not, save it. I am having troubles retaining the object after checking if it exists.

Here is an example of what I am trying to do. When I get to the success block, I need the original car object so that I can save it to the parse db. It is undefined though. I am new to JS and am probably missing something obvious here.

for (var j = 0, leng = cars.length; j < leng; ++j) {
    var car = cars[j];          
    var Car = Parse.Object.extend("Car");
    var query = new Parse.Query(Car);           
    query.equalTo("dodge", car.model);
    query.find({
      success: function(results) {
          if (results.length === 0) {
            //save car... but here car is undefined.
          } 
      },
      error: function(error) {
        console.error("Error: " + error.code + " " + error.message);
      }
    });
 }

If anyone could point me n the right direction, I would really appreciate it. Thanks!

Answer 1

Your function returns before the find method returns. This is the async nature of js. Use something like the async.parrallel from the async lib. http://npm.im/async

Update 20150929:

Here's some code to show you how I do it, this is from a side project I was working on. The data was stored in MongoDB and was accessed with the Mongoose ODM. I'm using Async waterfall as I need the value of the async function in the next method ... hence the name waterfall in the async lib. :)

 async.waterfall([
    // Get the topics less than or equal to the time now in utc using the moment time lib
    function (done) {
        Topic.find({nextNotificationDate: {$lte: moment().utc()}}, function (err, topics) {
            done(err, topics);
        });
    },
    // Find user associated with each topic
    function (topics, done) {
        // Loop over all the topics and find the user, create a moment, save it, 
        // and then send the email.
        // Creating moment (not the moment lib), save, sending email is done in the 
        // processTopic() method. (not showng)
        async.each(topics, function (topic, eachCallback) {
                processTopic(topic, eachCallback);
            }, function (err, success) {
                done(err, success);
            }
        );
    }
    // Waterfall callback, executed when EVERYTHING is done
], function (err, results) {
    if(err) {
        log.info('Failure!\n' + err)
        finish(1); // fin w/ error
    } else {
        log.info("Success! Done dispatching moments.");
        finish(0); // fin w/ success
    }
});

Answer 2

Promises will really simplify your life once you get used to them. Here's an example of an update-or-create pattern using promises...

function updateOrCreateCar(model, carJSON) {
    var query = new Parse.Query("Car");
    query.equalTo("model", model);
    return query.first().then(function(car) {
        // if not found, create one...
        if (!car) {
            car = new Car();
            car.set("model", model);
        }
        // Here, update car with info from carJSON.  Depending on
        // the match between the json and your parse model, there
        // may be a shortcut using the backbone extension
        car.set("someAttribute", carJSON.someAttribute);
        return (car.isNew())? car.save() : Parse.Promise.as(car);
    });
}

// call it like this
var promises = [];
for (var j = 0, leng = carsJSON.length; j < leng; ++j) {
    var carJSON = carsJSON[j];
    var model = carJSON.model;
    promises.push(updateOrCreateCar(model, carJSON));
}
Parse.Promise.when(promises).then(function() {
    // new or updated cars are in arguments
    console.log(JSON.stringify(arguments));
}, function(error) {
    console.error("Error: " + error.code + " " + error.message);
});