passing Tedious connection as parameter - sql

Question

I am trying to use a simple suite of functions built utilizing the Tedious library to access a Microsoft SQL Server. Here is my "tools" file:
'use strict';
const tedious = require('tedious');
const q = require('q');
var Connection = tedious.Connection;
var Request = tedious.Request;
module.exports = {
connectSQL : function(config) {
var connection = new Connection(config);
connection.on('connect', function(err) {
if (err) {
console.log('FAIL ON CONNECT');
console.log(err);
} else {
try {
/* ----- */
return connection;
} catch (err) {
console.log(err);
return;
}
}
});
connection.on('error', function(err) {
if (err) {
console.log('FAIL ON ERROR');
console.log(err);
} else {
console.log("Error called with no err object.");
}
});
},
executeSQL: function(connection, requestString) {
var results = [];
var request = new Request( requestString , function(err, data) {
if (err) {
console.log(err);
} else {
console.log( data );
}
});
request.on('row', function(row) {
//console.log(row);
results.push( row );
});
request.on('requestCompleted', function(){
console.log('Finished');
return results;
});
connection.execSql(request);
}
}
I call these functions as follows in my server file.
const sqlTools = require('./sqlTools.js');
var connection = sqlTools.connectSQL(config);
sqlTools.executeSQL(connection, "select * from dbo.test");
However, I get the error "TypeError: Cannot read property 'execSql' of undefined", even if I make the program sleep for 10 seconds before calling my function sqlTools.executeSQL (obviously not ideal).
I was able to get this to work by calling the request within the sqlTools.connectSQL function (at the "/* ----- */"), but I want to re-use the Tedious connection to make multiple calls. Any suggestions? Thanks!
~~~~~~~EDIT~~~~~~~~~~
With help from akinjide I was able to implement callbacks that allow me to make a single call to my SQL database. However, I am struggling to implement promises to make subsequent calls. I changed my "tools" file as such:
'use strict';
const tedious = require('tedious');
const q = require('q');
var Connection = tedious.Connection;
var Request = tedious.Request;
module.exports = {
connectSQL: function(config) {
var deferred = q.defer();
var connection = new Connection(config);
connection.on('connect', function(err) {
if (err) {
deferred.reject( err );
} else {
deferred.resolve( connection );
}
});
connection.on('error', function(err) {
deferred.reject(err);
});
return deferred.promise;
},
executeSQL: function(connection, requestString, callback) {
var results = [];
const request = new Request(requestString, function(err) {
callback(err);
});
request.on('row', function(row) {
results.push(row);
});
request.on('requestCompleted', function() {
console.log('request completed!');
callback(null, results);
});
connection.execSql(request);
}
}
and I call this code like this...
var promise = sqlTools.connectSQL(config);
promise.then(function (connection) {
sqlTools.executeSQL(connection, "select * from dbo.test", function(err, results) {
if (err) {
console.log(err);
}
console.log(results);
});
}).catch(function (err) {
console.log(err);
}).then(function (connection) {
sqlTools.executeSQL(connection, "select * from dbo.test2", function(err, results) {
if (err) {
console.log(err);
}
console.log(results);
});
}).catch(function(err) {
console.log(err);
});
This returns the first call's results correctly, but unfortunately returns this error "TypeError: Cannot read property 'execSql' of undefined" for the second call as it is not recognizing the connection the second time around. Any suggestions?

Answer 1

A better approach would be to pass a node.js callback style function as an argument to connectSQL.
return keyword won't work within an asynchronous program.
'use strict';
const tedious = require('tedious');
const Connection = tedious.Connection;
const Request = tedious.Request;
module.exports = {
connectSQL: function(config, callback) {
const connection = new Connection(config);
connection.on('connect', function(err) {
if (err) {
callback(err);
} else {
callback(null, connection);
}
});
connection.on('error', function (err) {
callback(err);
});
},
executeSQL: function(connection, requestString, callback) {
let results = [];
const request = new Request(requestString, function(err) {
callback(err);
});
request.on('row', function(row) {
results.push(row);
});
request.on('requestCompleted', function(){
console.log('Finished');
callback(null, results);
});
connection.execSql(request);
}
}
Then you can require, use sqlTools.connectSQL passing two parameters config and function(err, connection) {}
const sqlTools = require('./sqlTools');
sqlTools.connectSQL(config, function(err, connection) {
if (err) {
console.log('FAIL ON CONNECT');
console.log(err);
}
sqlTools.executeSQL(connection, "select * from dbo.test", function (err, results) {
if (err) {
console.log(err);
}
console.log(results);
});
});