Parse.com Javascript Asyn Call within Loop

Question

I have a list of company and would like to calculate a total amount of invoices issued to each company. The following is the code that I wrote. (Actual logic is more complicated within the loop but took them out here)

Basically I want to alert the message once the business logic within the loop is complete (Again, it will do something more complex here). I got a feeling that I can resolve this issue by using Promises but am not quite sure how to use it. I didn't quite follow Parse.com's document. I have been stuck with this for a few hours. Please help!

function calculate(companies) {

    companies.forEach(function(company) {

        var total = 0;

        var invoice = Parse.Object.extend('Invoice');
        var query = new Parse.Query(invoice);
        query.equalTo('invoiceCompany', company);

        query.find().then(function(invoices) {

            invoices.forEach(function(invoice) {

                total += parseFloat(invoice.get('amount'));

            });

        });
    });

    alert("Calculated Finished");
}

gmartini20 · Accepted Answer · 2015-06-23 15:59:54Z

2

You can use promises in paralell:

https://parse.com/docs/js/guide#promises-promises-in-parallel

It would be something like this:

function calculate(companies) {
  var promises = [];
  companies.forEach(function(company) {

      var total = 0;

      var invoice = Parse.Object.extend('Invoice');
      var query = new Parse.Query(invoice);
      query.equalTo('invoiceCompany', company);

      var queryPromise = query.find().then(function(invoices) {

          invoices.forEach(function(invoice) {

              total += parseFloat(invoice.get('amount'));

          });

      });

      promises.push(queryPromise);
  });

  return Parse.Promise.when(promises);

}

calculate(companies).then(function() {
  alert("Calculated Finished");
});

answered Jun 23, 2015 at 15:59

gmartini20

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1 Comment

david park Over a year ago

THanks! it works perfectly well..just one thing. When I got 1000 companies, the above code is extremely slow. It took about 10~15 seconds to complete the transaction. How could I improve the query?

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