CODEWITHSUNDEEP
javascriptnode.jsasynchronous
user2085689
user2085689

Reputation: 336

Nodejs SQL connections and async module

I been playing along with Node.JS and I found this great async library https://github.com/caolan/async. I want to replace the traditional callback model with this, as it looks a bit more pleasing and easier to understand.

This is my code for sql query

function query_mssql(config, sql_string){
  var connection = new sql.Connection(config, function(err) {
  // ... error checks 

  if (err) {
    console.log('connection to mssql has failed');
    //throw err;
  }else{

    // Query 
    var request = new sql.Request(connection); // or: var request = connection.request(); 
    request.query(sql_string, function(err, recordset) {
        // ... error checks should go here :

        // output query result to console:
        console.log(recordset);
        return recordset;
    });

  }

}); }

I am wondering how to make this async, like the example given in the library.

    async.series([
    function(callback){
        // do some stuff ...
        callback(null, 'one');
    },
    function(callback){
        // do some more stuff ...
        callback(null, 'two');
    }
   ],
   // optional callback
   function(err, results){
    // results is now equal to ['one', 'two']
   });

Can someone help me with this? I don't quite understand how the error reporting works.

Based on Chris's comment, how exactly will the waterfall method help if called in multi layered?

function computeCurrentDefinitionResult(database, node_name) {
async.waterfall([
    function(callback) {
      var leaf_sql_query = "SELECT * FROM "+  JSON.stringify(database)  +".dbo.LeafNode WHERE NodeName=" + "'" + node_name + "'";
      query_mssql_internal(leaf_sql_query, callback);
      console.log('Might BE HAPPY');
    },
], function(err, recordset) {
    // ... error checks should go here :
    if (err) {
        console.log('mssql query has failed');
    }

    // output query result to console:
    console.log(recordset);
    return recordset;
  });

function query_mssql_internal(sql_string){
  return query_mssql(config, sql_string);
}

the "query_mssql()" call your function. How do pass on result back to top calling function or the error back?

Upvotes: 1

Views: 2002

Answers (1)

Chris
Chris

Reputation: 2806

For this I believe you should use async.waterfall since you want to pass results along each async task.

Here is a quick example below. You'll have to edit it to suit your needs.

If an error happens in a task, it'll move out to the optional method at the end.

async.waterfall([
    function(callback) {
        var connection = new sql.Connection(config, 
            function(err) {
                callback(err, connection)
            }
        );
    },
    function(connection, callback) {
        var request = connection.request(); 
        request.query(sql_string, callback);
    }
], function(err, recordset) {
    // ... error checks should go here :

    // output query result to console:
    console.log(recordset);
});

As you see, you can add parameters after the error in your callback and then receive them in the next task. This is a feature of async.waterfall.

Here is a test example as well...

require("should");
var async = require("async");
describe("async test", function() {
   it('should do stuff', function(done){

       async.waterfall([
           function(callback){
               a(callback);
           },
           function(aResult, callback){
               b(callback, aResult);
           }
       ], function(err, aResult, bResult) {
           console.log(aResult + " " + bResult);
           done();
       });

       function a(callback) {
           callback(null, 1);
       }
       function b(callback, aResult) {
           callback(null, aResult, 2);
       }

   })
});

As for your last edit, you must return your value asynchronously. So you cannot use a return statement to get your result. This has a trickle effect which causes those dependencies to become asynchronous as well.

Upvotes: 1

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