Asynchronous loops In Javascript/node.js

Question

I am working with node js and postgresql. I tried to insert multiple query at a time.

ArrayList:

var keywordsData =  [ { name: 'demo', count: 69 }, { name: 'healthy', count: '22' }, { name: 'cooking', count: '12' }, { name: 'food', count: '9' }, { name: 'home', count: '9' }, { name: 'organic', count: '7' }, { name: 'live', count: '6' }, { name: 'openmrs', count: '6' }];

Javascript code:

   for (var indexs in keywordsData) {
          var item = keywordsData[indexs].name;
          var count = keywordsData[indexs].count;
          var goalId = 10;

          console.log("first" + indexs);
          if (item.length > 1) {
          client.query("insert into real_keywords(reference_id,keyword,keyword_count) values('" + goalId + "','" + item + "','" + count + "')", function(err, result) {
          console.log("last" + indexs);
          });

          }
    }

Output i am getting like this:

first0
first1
first2
first3
first4
first5
first6
first7
last7
last7
last7
last7
last7
last7
last7
last7

Expected output:

first0
last0
first1
last1
first2
last2
first3
last3
first4
last4
first5
last5
first6
last6
first7
last7

Please anyone can suggest the best way to solve this.

Ok, this is slightly off topic, so not adding it as an answer. @IyadAssaf answer is correct in regards to async. But you should check out two other bits for your SQL queries 1) Not sure what the size of indexes is, but you can insert all your rows at once. stackoverflow.com/questions/6889065/… 2) You should consider using a prepared statement instead of string concatenation. postgresql.org/docs/9.2/static/sql-prepare.html — Alex Hornbake
– Alex Hornbake, Commented Jun 10, 2015 at 12:02

IyadAssaf · Accepted Answer · 2015-06-10 11:55:32Z

2

The for loop is synchronous whereas the postgres query you are running is asynchronous - the loop is not waiting for the database callback before iterating.

Probably the easiest way to make this work is to use the async library's each function. For example:

 var async = require('async'),
     values = [{ name: 'demo', count: 69 }, { name: 'healthy', count: '22' }];

async.each(values, function (value, done) {
    client.query('Some query using value.name and value.count', function (err, result) {
        // query is finished
        done(err, result);
    });
 }, function (err) {
      // all queries have finished
 });

edited Jun 10, 2015 at 11:55

answered Jun 10, 2015 at 11:36

IyadAssaf

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1 Comment

throrin19 Over a year ago

you should use each to loop on array, map is used to return new array

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