Preserving items post-parse query in cloud code

Question

Preserving items post-parse query in cloud code

Currently, I am in the process of developing Parse Cloud Code to retrieve JSON data from a third-party API. My goal is to make modifications to the data, check if it already exists, and save it if it doesn't. However, I am encountering difficulties in retaining the object after the verification process.

Here's an illustration of the issue I am facing. Upon reaching the success block, I require the original 'car' object to be able to store it in the Parse database. Sadly, the object is undefined at this point. As a newcomer to JavaScript, I acknowledge that there may be something obvious that I am overlooking.

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... however, 'car' is undefined here.
          } 
      },
      error: function(error) {
        console.error("Error: " + error.code + " " + error.message);
      }
    });
 }

If anyone could steer me in the right direction, I would greatly appreciate it. Thank you!

javascript json parse-platform parse-cloud-code

Answer 1

Answer №1

Mastering promises can greatly enhance your efficiency in handling asynchronous tasks. Take a look at this implementation of an update-or-create pattern using promises...

function updateOrCreateVehicle(type, vehicleDetails) {
    var query = new Parse.Query("Vehicle");
    query.equalTo("type", type);
    return query.first().then(function(vehicle) {
        // if not found, create a new one...
        if (!vehicle) {
            vehicle = new Vehicle();
            vehicle.set("type", type);
        }
        // Update the vehicle with information from vehicleDetails. 
        vehicle.set("attribute", vehicleDetails.attribute);
        return (vehicle.isNew())? vehicle.save() : Parse.Promise.as(vehicle);
    });
}

// Usage example
var promises = [];
for (var i = 0, length = vehiclesJSON.length; i < length; ++i) {
    var vehicleDetails = vehiclesJSON[i];
    var type = vehicleDetails.type;
    promises.push(updateOrCreateVehicle(type, vehicleDetails));
}
Parse.Promise.when(promises).then(function() {
    // Access new or updated vehicles through arguments
    console.log(JSON.stringify(arguments));
}, function(error) {
    console.error("Error: " + error.code + " " + error.message);
});

Answer 2

Mastering promises can greatly enhance your efficiency in handling asynchronous tasks. Take a look at this implementation of an update-or-create pattern using promises...

function updateOrCreateVehicle(type, vehicleDetails) {
    var query = new Parse.Query("Vehicle");
    query.equalTo("type", type);
    return query.first().then(function(vehicle) {
        // if not found, create a new one...
        if (!vehicle) {
            vehicle = new Vehicle();
            vehicle.set("type", type);
        }
        // Update the vehicle with information from vehicleDetails. 
        vehicle.set("attribute", vehicleDetails.attribute);
        return (vehicle.isNew())? vehicle.save() : Parse.Promise.as(vehicle);
    });
}

// Usage example
var promises = [];
for (var i = 0, length = vehiclesJSON.length; i < length; ++i) {
    var vehicleDetails = vehiclesJSON[i];
    var type = vehicleDetails.type;
    promises.push(updateOrCreateVehicle(type, vehicleDetails));
}
Parse.Promise.when(promises).then(function() {
    // Access new or updated vehicles through arguments
    console.log(JSON.stringify(arguments));
}, function(error) {
    console.error("Error: " + error.code + " " + error.message);
});

Answer 3

Answer №2

Your function returns before the find method completes its operation. This asynchronous behavior is a characteristic of JavaScript. You can implement a solution using the async parallel function from the async library.

Updated on 20150929:

Below is an example code snippet demonstrating how I handle this scenario in a side project. The data is stored in MongoDB and accessed using the Mongoose ODM. I utilize Async waterfall to ensure proper sequencing of asynchronous operations. This enables me to pass values between functions and ensure execution order. Here's a snippet of the code:

 async.waterfall([
    // Retrieve topics with notification dates less than or equal to the current UTC time using the moment.js library
    function (done) {
        Topic.find({nextNotificationDate: {$lte: moment().utc()}}, function (err, topics) {
            done(err, topics);
        });
    },
    // Find user associated with each topic
    function (topics, done) {
        // Iterate over topics to find users, perform necessary actions, and send emails
        async.each(topics, function (topic, eachCallback) {
                processTopic(topic, eachCallback);
            }, function (err, success) {
                done(err, success);
            }
        );
    }
    // Final callback for waterfall, executes when all operations are completed
], function (err, results) {
    if(err) {
        log.info('Operation Failed!\n' + err)
        finish(1); // exit with error
    } else {
        log.info("Operation Successful! Moments dispatched.");
        finish(0); // exit with success
    }
});

Answer 4

Your function returns before the find method completes its operation. This asynchronous behavior is a characteristic of JavaScript. You can implement a solution using the async parallel function from the async library.

Updated on 20150929:

Below is an example code snippet demonstrating how I handle this scenario in a side project. The data is stored in MongoDB and accessed using the Mongoose ODM. I utilize Async waterfall to ensure proper sequencing of asynchronous operations. This enables me to pass values between functions and ensure execution order. Here's a snippet of the code:

 async.waterfall([
    // Retrieve topics with notification dates less than or equal to the current UTC time using the moment.js library
    function (done) {
        Topic.find({nextNotificationDate: {$lte: moment().utc()}}, function (err, topics) {
            done(err, topics);
        });
    },
    // Find user associated with each topic
    function (topics, done) {
        // Iterate over topics to find users, perform necessary actions, and send emails
        async.each(topics, function (topic, eachCallback) {
                processTopic(topic, eachCallback);
            }, function (err, success) {
                done(err, success);
            }
        );
    }
    // Final callback for waterfall, executes when all operations are completed
], function (err, results) {
    if(err) {
        log.info('Operation Failed!\n' + err)
        finish(1); // exit with error
    } else {
        log.info("Operation Successful! Moments dispatched.");
        finish(0); // exit with success
    }
});

Preserving items post-parse query in cloud code

Answer №1

Answer №2

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