Develop Reference

SQlite result undefined issue in NodeJS [duplicate]

How do I get the return value from inside a value of node.js/javascript callback?
function get_logs(){
User_Log.findOne({userId:req.user._id}, function(err, userlogs){
if(err) throw err;
if(userlogs){
// logs = userlogs.logs;
return "hello there is a logs";
} else {
return "there is no logs yet..."
}
})
}
var logs = get_logs();
console.log(logs);

You can't return the result from a function whose execution is asynchronous.
The simplest solution is to pass a callback :
function get_logs(cb){
User_Log.findOne({userId:req.user._id}, function(err, userlogs){
if(err) throw err;
if(userlogs){
// logs = userlogs.logs;
cb("hello there is a logs");
} else {
cb("there is no logs yet...)"
}
})
}
get_logs(function(logs){
console.log(logs);
});

You can't. You should instead pass another callback to your function. Something like this:
function get_logs(callback){
User_Log.findOne({userId:req.user._id}, function(err, userlogs){
if(err) throw err;
if(userlogs){
callback("hello there is a logs");
} else {
callback("there is no logs yet...");
}
})
}
get_logs(function(arg1) {
console.log(arg1);
});

function get_logs(callback) {
User_Log.findOne({
userId: req.user._id
}, function (err, userlogs) {
if (err) throw err;
if (userlogs) {
// logs = userlogs.logs;
callback("hello there is a logs");
} else {
callback("there is no logs yet...");
}
})
}
get_logs(function (data) {
console.log(data);
});
Uses callbacks...

In node.js almost all the callbacks run after the function returns , so you can do something like this
function get_logs(){
User_Log.findOne({userId:req.user._id}, function(err, userlogs){
if(err) throw err;
if(userlogs){
// logs = userlogs.logs;
do_something(logs)
} else {
console.log('No logs')
}
})
}

mongodb nodejs store value outside connect

I need a way to store value outside mongoDB connect call:
read(object) {
let result
MongoClient.connect(this.url, function (err, db) {
if (err!=null){
result = err;
} else {
db.collection(object.collection).find(object.field).toArray(function(err, docs) {
assert.equal(err, null);
db.close();
result = docs;
});
}
});
return result
}
When i call this method, which is part of a class, return is called before result assignment, as normal.
Example: console.log(read(obj)) returns undefined
The idea is to store value in a variable and return might wait until connect terminate.
Is there any way to resolve this problem?

Without promise:
Call return inside find and err function:
read(object) {
let result
MongoClient.connect(this.url, function (err, db) {
if (err!=null){
result = err;
return result; //here
} else {
db.collection(object.collection).find(object.field).toArray(function(err, docs) {
assert.equal(err, null);
db.close();
result = docs;
return result; // here
});
}
});
}
Or set a timeout for return with enough time to wait for other process to end:
read(object) {
let result
MongoClient.connect(this.url, function (err, db) {
if (err!=null){
result = err;
} else {
db.collection(object.collection).find(object.field).toArray(function(err, docs) {
assert.equal(err, null);
db.close();
result = docs;
});
}
});
setTimeout(function(){ return result}, 3000); // 3secs
}

With Promise you can try the following:
function read(object) {
let result
return new Promise((resolve, reject) => {
MongoClient.connect(this.url, function (err, db) {
if (err!=null){
reject(err);
} else {
db.collection(object.collection).find(object.field).toArray(function(err, docs) {
db.close();
if (err) {
reject(err);
} else {
resolve(docs);
}
});
}
});
});
}
// then you can call the function and use the result like this
read(obj).then(docs => {
console.log(docs);
})
.catch(err => {
// handle error
console.log(err);
})

how to return array in Node.js from module

getting undefined all the time "main.js":
var dbAccess = require('../dao/dbAccess');
dbaInstance = new dbAccess();
var wordPool = dbaInstance.getWordPool();
console.log (wordPool);
and "dbAccess.js" contains:
var DatabaseAccess = function() {}
DatabaseAccess.prototype.getWordPool = function () {
RoundWord.find({},'words decoys', function(err, wordPoolFromDB) {
if (err) throw err;
//console.log(wordPoolFromDB); -working ok
return (wordPoolFromDB);
});
}
module.exports = DatabaseAccess;
why is it not working?

DatabaseAccess.prototype.getWordPool is not returning any result.
Since you are using an asynchronous function, you need do one of these things:
a) Take a callback as parameter and invoke the callback with a result
DatabaseAccess.prototype.getWordPool = function (cb) {
RoundWord.find({}, 'words decoys', function(err, results) {
if (err) {
return cb(err, null);
}
cb(null, results);
});
}
The callback convention is: cb(error, results...)
b) Use promises
DatabaseAccess.prototype.getWordPool = function () {
return RoundWord.find({}, 'words decoys', function (err, results) {
if (err) {
throw err; // however you might want to sanitize it
}
return results;
});
}
To consume this result you will need to do it as a promise
databaseAccess.getWordPool()
.catch(function (err) {
// process the error here
})
.then(function (results) {
// something with results
});

It will work if you change to this:
var dbAccess = require('../dao/dbAccess');
dbaInstance = new dbAccess();
dbaInstance.getWordPool(function(wordPool){console.log (wordPool);});
And:
var DatabaseAccess = function() {}
DatabaseAccess.prototype.getWordPool = function (cb) {
RoundWord.find({},'words decoys', function(err, wordPoolFromDB) {
if (err) throw err;
//console.log(wordPoolFromDB); -working ok
cb(wordPoolFromDB);
});
}
module.exports = DatabaseAccess;

If the function is Asynchronous you need to pass a callback to find to get the result:
DatabaseAccess.prototype.getWordPool = function (callback) {
RoundWord.find({},'words decoys', function(err, wordPoolFromDB) {
if (err) throw err;
callback(err, wordPoolFromDB);
});
}
and call it as follows in main:
dbaInstance.getWordPool(function (err, wordPool) {
console.log (wordPool);
// wordPool is only available inside this scope,
//unless assigned to another external variable
});
// cannot access wordPool here

returning data from node mssql execute functions

I'm using mssql(Microsoft SQL Server client for Node.js) package from npm.I'm trying to execute a stored procedure residing in my sql server database.Everything works fine.However what I want to do is return the recordsets so that i can export this to be used in other module.Below is what I'm trying to do.
function monthlyIceCreamSalesReport (scope){
var connObj = connConfig();
connObj.conn.connect(function(err){
if(err){
console.log(err);
return;
}
connObj.req.input('Month',4);
connObj.req.input('Year',2016);
connObj.req.execute('<myStoredProcedure>', function(err, recordsets, returnValue){
if(err){
console.log(err);
}
else {
console.log(recordsets[0]); // successfully receiving the value
}
connObj.conn.close();
});
});
console.log('check for recordsets', recordsets[0]); // undefined
return recordsets[0];
}
var sqlServerObj = {
monICSalesReport : monthlyIceCreamSalesReport,
};
module.exports = sqlServerObj;
As shown in the code snippet, since the value of recordsets[0] is undefined, exporting this function is of no use.

You can't return this way in async nature. You can get it by passing the callback function
Try to give a callback function like this
function monthlyIceCreamSalesReport(scope, callback) { // pass a callback to get value
var connObj = connConfig();
connObj.conn.connect(function(err) {
if (err) {
console.log(err);
return;
}
connObj.req.input('Month', 4);
connObj.req.input('Year', 2016);
connObj.req.execute('<myStoredProcedure>', function(err, recordsets, returnValue) {
if (err) {
console.log(err);
} else {
console.log(recordsets[0]);
connObj.conn.close();
return callback(null, recordsets[0]); //return as a callback here and get that value in callback from where you called this function
}
});
});
}
var sqlServerObj = {
monICSalesReport: monthlyIceCreamSalesReport,
};
module.exports = sqlServerObj;
Note: See the comment to understand the changes

recordsets[0] is undefinded, because is defined only in connObj.req.execute function scope. You may do this in this way:
function monthlyIceCreamSalesReport (scope, cb){
var connObj = connConfig();
connObj.conn.connect(function(err){
if(err){
console.log(err);
return cb(Error("Something wrong"));
}
connObj.req.input('Month',4);
connObj.req.input('Year',2016);
connObj.req.execute('<myStoredProcedure>', function(err, recordsets, returnValue){
if(err){
console.log(err);
connObj.conn.close();
return cb(Error("Something wrong"));
}
else {
console.log(recordsets[0]); // successfully receiving the value
connObj.conn.close();
return cb(recordsets[0]);
}
});
});
}
var sqlServerObj = {
monICSalesReport : monthlyIceCreamSalesReport,
};
module.exports = sqlServerObj;

Connection.query to execute

Pretty sure this is a quite noobish node.js/callback question but I can't seem to find the proper code to make it run.
This is how I invoke my node-mysql code:
var utils = require('../../config/database/utils');
exports.getResults = function(callback) {
var query = "SELECT * FROM my_table";
utils.exec(query, null, function(err, results){
if(err){
console.log(err);
callback(true);
return;
}
console.log(results);
callback(false, results);
});
};
Next is the utils file where I can't get the code work.
var pool = require('./connection');
module.exports = {
getDBConnection: function() {
pool.getConnection(function(err, connection){
if(err){
console.log(err);
return;
}
return connection;
});
},
endDBConnection: function(connection) {
connection.end(function (err) {
if(err) {
console.log(err);
callback(true);
return;
}
});
},
exec: function(query, data, callback) {
console.log(query);
this.getDBConnection(function(err, connection){
if(err){
console.log('error');
}
console.log(connection);
connection.query(query, data, function(err, results) {
if(err) {
callback(err);
}
callback(false, results);
});
this.endDBConnection(connection);
});
}
}
Code is getting OK the the exec part since the console.log(query) logs the query. But after that, the code's not running, console.log(connection); doesn't show a thing, and of course the connection.query is also not running.
I'm not sure why this is happening.

Returning a value inside a callback is meaningless. You need to pass in a callback that gets called with the value you want to return:
getDBConnection: function(callback) {
pool.getConnection(function(err, connection){
if(err){
console.log(err);
return callback(err);
}
callback(null, connection);
});
},
You should also use connection.release() instead of connection.end() since you are using a pool:
endDBConnection: function(connection) {
connection.release();
},
In exec(), you have the wrong this. It should instead be something like:
exec: function(query, data, callback) {
console.log(query);
var self = this;
this.getDBConnection(function(err, connection){
if(err){
console.log('error');
return callback(err);
}
console.log(connection);
connection.query(query, data, function(err, results) {
self.endDBConnection(connection);
if(err) {
return callback(err);
}
callback(null, results);
});
});
}