Nodejs async.each wait for first loop

Question

I am trying to process rowsArr (lets say 100 records) asynchronous but I want to load country list from database only one time to avoid database connections. I am trying below example code but it is opening database connections 100 times.

var countryList = null;

async.each(rowsArr, function(row, callback) {


    if( countryList == null )
    {
        console.log("open database here to get country list and then assign to below variable");

        countryList = countriesFromDatabase;

        callback( countryList );
    }
    else
    {
        callback( countryList );
    }


}, function(err){

      console.log("all rows are processed");

});

It is working fine with async.eachSeries but I want it in asynchronous manner. Any suggestion?

Jagdish Idhate · Accepted Answer · 2016-04-27 12:58:49Z

3

Get Countries from database
Process all rows

So following will work

function getCountries(callback) {
  console.log("open database here to get country list and then assign to below variable");
  callback(null,countriesFromDatabase);
}
getCountries(function(err, countriesFromDatabase) {
 // use countries in following async loop
  async.each(rowsArr, function(row, callback) {
    callback(null, row); //process row here
  }, function(err) {
    console.log("all rows are processed");
  });
});

answered Apr 27, 2016 at 12:58

Jagdish Idhate

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4 Comments

Mohd Shahid Over a year ago

this approach is good but my above function is already inside another loop. So 100 records are to process in one loop and there are millions of records.

Jagdish Idhate Over a year ago

I'm assuming until you get countriesFromDatabase you can not process row, so still if I get countriesFromDatabase in first iteration, other rows will not have countriesFromDatabase(being asynchronous) So my guess u need to change function a bit

Ironcache Over a year ago

This is almost certainly the right answer to the question as posted. I'd either edit the question to reflect why this answer doesn't work, or accept it.

Mohd Shahid Over a year ago

I will change my code logic as per giving suggestion. Thanks.

st. · Accepted Answer · 2016-04-27 13:00:44Z

0

It does what it should actually, all hundred rows processing starts at the same time and they're passing the if block.

You might want to use locks. https://github.com/BorisKozo/node-async-locks

That way you can lock your countryList checking process to avoid multiple database connections.

answered Apr 27, 2016 at 13:00

st.

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