Node.js async.each等待第一个循环

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?

Answer 1

1. Get Countries from database
2. 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");
  });
});

Answer 2

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.