I have a server that is written in Java running Rhino for js,
and I decide to rewrite this server into nodejs...
And I need to get data from DB synchronous like :
function executeRowsetParam(sql, p){
return DB.raw(sql,p)// returns object
}
so I can use it like :
var userName = executeRowsetParam('SELECT user_name FROM users where user_id = ?', ["123"]);
if(userName.getRow(0).getValue("user_name ") == "admin"){
//do sth
}
is just an a simple example sometimes I need to select from database data that i have to use in like 1000 lines of code so code like :
executeRowsetParam('SELECT user_name FROM users where user_id = ?', ["123"]).then((r)=>{
if(r.getRow(0).getValue("user_name ") == "admin"){
//do sth
}
})
won't work so well ...
I have code like this too:
IfExists(SQL,p){
if(DB.raw("selecect top 1 1 from" + sql,p) == 1){
return true
}else{return false}
and rewriting it into :
DB.raw("selecect top 1 1 from" + sql,p).then((r)=>{
if(r == 1){//do sth}else{//do else}
})
won't work for me
so is there some npm package that I can use to make selects from db synchronuch that would make my day.
is code like this would be okey ?
var Start = async () => {
var Server = require("./core/server/Server");
console.log('hi!');
console.dir("there is nothing to look at at the momment");
var db = require("./core/db/DB");
global.DB = new db()
function foo() {
return DB.executeSQL("asdasd", [123, 123])
}
console.dir(await foo());
console.dir('asd');
global.DEBUG = true;
global.NEW_GUID = require('uuid/v4');
var server = new Server()
server.start();
}
Start();
is that enough to let me use await in every single instance inside the server or have I make every single function async if I would use await?
Found and tested deasync works great!
var deasync = require('deasync');
module.exports = function DB(){
var knex = require('knex')(require("./../../config").DB);
this.executeRowsetParam = (sql, param) => {
let done = false;
knex.raw(sql, param).then((r => {
done = r;
})).catch((e => {
throw "Error in query "+ e
}))
deasync.loopWhile(function () { return !done; });
return done
}
}
Related
I'm trying to check if a user exists (registered on a json file).
Unfortunately I don't find a valid solution in all Stack Overflow that gives me a simple "true" in a callback.
The version closest to a solution
Experiment V1 :
let userExist;
function check(){
console.log("CHECK!");
return userExist = true;
}
// check(); if this, return true... obvious.
//// check if user exist
server.readFileSync(filepath, 'utf8', (err, data) =>
{
let json = JSON.parse(data),
userlist = json.allusers;
for (let key in userlist)
{
if ( userlist[key].email == req.body.user_email )
{
console.log("FINDED EQUAL");
check(); // return undefined ???
}
}
});
console.log("userExist value : "+userExist);
differently formulated the debugs also appear, but "true" never returns.
note: yes, JSON is read correctly. If everything works inside the readfile, you immediately notice the same emails.
output: "undefined"
Log: total bypassed
Experiment V2 :
In this case (with asynchronous reading) it returns all the debugging (but the "true" remains undefined)
The problem with the asynchronous is that I have to wait for it to check to continue with the other functions.
//// check if user exist
server.readFile(filepath, 'utf8', (err, data) =>
{
let json = JSON.parse(data),
userlist = json.allusers;
for (let key in userlist)
{
if (/* json.allusers.hasOwnProperty(key) &&*/ userlist[key].email == req.body.user_email )
{
console.log("FINDED EQUAL");
check();
}
}
});
var userExist;
function check(userExist){
console.log("CHECK!");
return userExist=true;
}
console.log("userExist value : "+userExist+"");
server listening on: 8080
userExist value : undefined
CHECK!
FINDED EQUAL
Experiment V3 :
after the various suggestions I come to a compromise by using the syntax for the async functions.
This allowed to reach an ordered code, but despite this it is not possible to wait for the results and export them out of the same function (this is because node itself is asynchronous! Therefore it has already gone on!)
using a "message" variable to check if it could return an object I did so:
//simple output tester
var message;
// create a promise
let loopusers = new Promise( (resolve)=>{
server.readFile( filepath, 'utf8',
(err, data) => {
let json = JSON.parse(data),
userlist = json.allusers,
findedequal;
console.log("CHECK USERS IN DB...for "+userlist.length+" elements");
// loop all items
for (let key in userlist)
{
console.log("Analyzed key ::: "+key);
if ( userlist[key].email == req.body.user_email )
{
console.log("CHECK : user isn't free");
findedequal=true;
resolve(true); // return the result of promise
}
else if(key >= userlist.length-1 && !findedequal )
{
console.log("CHECK : User is free ;)");
resolve(false); // return the result of promise
}
}
// call the action
createuser();
});
});
// when promise finished --> start action
async function createuser(message)
{
let userExist = await loopusers;
console.log("userExist: "+userExist);
if(userExist)
{
message = { Server: "This user already exists, Try new e-mail..."};
}
else
{
message = { Server: "Registration user -> completed..."};
}
// return values
return message;
};
It is also possible to use the classic syntax via "then". For exemple:
//simple output tester
var message;
// create a promise
let loopusers = new Promise( (resolve)=>{
...
});
loopusers.then( (response)=>{
...
})
Then I realized that it was easy to simplify even more by calling the functions directly from the initial one:
var message;
// create a promise --> check json items
server.readFile( filepath, 'utf8',
(err, data) => {
let json = JSON.parse(data),
userlist = json.allusers,
findedequal;
console.log("CHECK USERS IN DB...for "+userlist.length+" elements");
for (let key in userlist)
{
console.log("Analyzed key ::: "+key);
if ( userlist[key].email == req.body.user_email )
{
console.log("CHECK : user isn't free");
findedequal=true;
createuser(true); // call direct function whit params true
}
else if(key >= userlist.length-1 && !findedequal )
{
console.log("CHECK : User is free ;)");
createuser(false); // call direct function whit params false
}
}
});
// start action
function createuser(userExist)
{
if(userExist)
{
message = { Server: "This user already exists, Try new e-mail..."};
}
else
{
message = { Server: "Registration user -> completed!"};
}
// return values
return message;
};
debugging is taken and written
the message is lost outside the aSync function
Experiment V4 Final! :
Finally, after many attempts the solution! (Yes... But know it's not Async)
If we allocate in a variable the reading becomes synchronous the whole model and we return to the simple one
let message,
file = server.readFileSync(filepath, 'utf8'), // read sync
json = JSON.parse(file), // now parse file
userlist = json.allusers, // get your target container object
userExist,
findedequal;
console.log("CHECK USERS IN DB...for "+userlist.length+" elements");
for (let key in userlist)
{
console.log("Analyzed key ::: "+key);
if ( userlist[key].email == req.body.user_email )
{
console.log("CHECK : finded equal value on key ["+key+"] - user isn't free");
findedequal=true;
userExist = true;
}
else if(key >= userlist.length-1 && !findedequal )
{
console.log("CHECK : User is free ;)");
userExist = false;
}
}
if(userExist)
{
console.log("└ EXIT TO CHECK --> Can't create user, function stop.");
message = { Server: "This user already exists, Try new e-mail..."};
}
else
{
console.log("└ Exit to check --> New user registration ...");
message = { Server: "Registration user -> completed!"};
}
}
return message;
Now:
It's all sync and all log is perfect
all var is checked
all return... return
** Final conclusions: **
Is it possible to retrieve an ASync variable in node?
As far as I understand so far ... no.
Node is async by its nature, therefore recovering information that is not saved and then recovered from a DB is left behind among the things to do, becoming unrecoverable if you use it as in this post.
However ... if the purpose is to make reading a file synchronous, the answer was simpler than expected.
A special thanks to: Barmar; Austin Leehealey; C.Gochev;
The problem is that you are calling console.log("userExist value : "+userExist+"");
too early. At the moment that you call that line, userExist is not defined yet. This is because the server.readFile() function requires a callback and that callback function is executed once it has read the file. However, reading files often take time and so the program keeps going. It executes console.log("userExist value : "+userExist+""); and then goes back to the callback function and defines userExist as true.
If you want more information on what callbacks are look at the link below. Callbacks are a defining feature of Nodejs and understanding them is essential to any Node website.
https://medium.com/better-programming/callbacks-in-node-js-how-why-when-ac293f0403ca
Try something like this.
let userExist;
function check(){
console.log("CHECK!");
return userExist = true;
}
// check(); if this, return true... obvious.
//// check if user exist
server.readFileSync(filepath, 'utf8', (err, data) =>
{
let json = JSON.parse(data),
userlist = json.allusers;
for (let key in userlist)
{
if ( userlist[key].email == req.body.user_email )
{
console.log("FINDED EQUAL");
check(); // return undefined ???
console.log("userExist value : "+userExist);
}
}
});
I'm new to learning Node.js, so I'm still getting used to asynchronous programming and callbacks. I'm trying to insert a record into a MS SQL Server database and return the new row's ID to my view.
The mssql query is working correctly when printed to console.log. My problem is not knowing how to properly return the data.
Here is my mssql query - in addJob.js:
var config = require('../../db/config');
async function addJob(title) {
var sql = require('mssql');
const pool = new sql.ConnectionPool(config);
var conn = pool;
let sqlResult = '';
let jobID = '';
conn.connect().then(function () {
var req = new sql.Request(conn);
req.query(`INSERT INTO Jobs (Title, ActiveJD) VALUES ('${title}', 0) ; SELECT ##IDENTITY AS JobID`).then(function (result) {
jobID = result['recordset'][0]['JobID'];
conn.close();
//This prints the correct value
console.log('jobID: ' + jobID);
}).catch(function (err) {
console.log('Unable to add job: ' + err);
conn.close();
});
}).catch(function (err) {
console.log('Unable to connect to SQL: ' + err);
});
// This prints a blank
console.log('jobID second test: ' + jobID)
return jobID;
}
module.exports = addJob;
This is my front end where a modal box is taking in a string and passing it to the above query. I want it to then receive the query's returned value and redirect to another page.
// ADD NEW JOB
$("#navButton_new").on(ace.click_event, function() {
bootbox.prompt("New Job Title", function(result) {
if (result != null) {
var job = {};
job.title = result;
$.ajax({
type: 'POST',
data: JSON.stringify(job),
contentType: 'application/json',
url: 'jds/addJob',
success: function(data) {
// this just prints that data is an object. Is that because I'm returning a promise? How would I unpack that here?
console.log('in success:' + data);
// I want to use the returned value here for a page redirect
//window.location.href = "jds/edit/?jobID=" + data;
return false;
},
error: function(err){
console.log('Unable to add job: ' + err);
}
});
} else {
}
});
});
And finally here is the express router code calling the function:
const express = require('express');
//....
const app = express();
//....
app.post('/jds/addJob', function(req, res){
let dataJSON = JSON.stringify(req.body)
let parsedData = JSON.parse(dataJSON);
const addJob = require("../models/jds/addJob");
let statusResult = addJob(parsedData.title);
statusResult.then(result => {
res.send(req.body);
});
});
I've been reading up on promises and trying to figure out what needs to change here, but I'm having no luck. Can anyone provide any tips?
You need to actually return a value from your function for things to work. Due to having nested Promises you need a couple returns here. One of the core features of promises is if you return a Promise it participates in the calling Promise chain.
So change the following lines
jobID = result['recordset'][0]['JobID'];
to
return result['recordset'][0]['JobID']
and
req.query(`INSERT INTO Jobs (Title, ActiveJD) VALUES ('${title}', 0) ; SELECT ##IDENTITY AS JobID`).then(function (result) {
to
return req.query(`INSERT INTO Jobs (Title, ActiveJD) VALUES ('${title}', 0) ; SELECT ##IDENTITY AS JobID`).then(function (result) {
and
conn.connect().then(function () {
to
return conn.connect().then(function () {
You may need to move code around that is now after the return. You would also be well served moving conn.close() into a single .finally on the end of the connect chain.
I recommend writing a test that you can use to play around with things until you get it right.
const jobId = await addJob(...)
console.log(jobId)
Alternatively rewrite the code to use await instead of .then() calls.
I have nodejs-mongo setup with db configured as follows (only one entry shown here)
{
"filename":"type1.json","secs":72.4060092977,"platform":"mac","version":"1.3.0", "inputfile":"temp.mov"
},
Here are the mongo commands I am trying to replicate
db.perfR.distinct("platform") * (output: ["mac", "win"] ) *
db.perfR.distinct("version",{"platform":"win"}) * (output: ["1.3.0", "1.3.2"] ) *
db.perfR.find({"version":1.3.2,"platform":"win"},{"filename":1,"secs":1,"_id":0}) * (output: ["filename":"type1.json","secs":72.4060092977] ) *
So what I am trying to do is
for every platform
for every version
get filename
get secs
Here is the code I have written thus far
function createPlatformDataSets(callback){
var dbHost = "mongodb://mongo:27017/perfSample";
var mongodb = require('mongodb')
var platformDataSets = []
var platformq = "platform"
//get Instance of Mongoclient
var MongoClient = mongodb.MongoClient;
//Connecting to the Mongodb instance.
//Make sure your mongodb daemon mongod is running on port 27017 on localhost
MongoClient.connect(dbHost, function(err, db){
if ( err ) throw err;
//use the distinct() to retrive distinct platforms
db.collection("perfR").distinct(platformq,function(err, platResultSet){
if ( err ) throw err;
var maxPlatCnt = platResultSet.length // 1
if (maxPlatCnt == 0){
console.log("Bad PlatfQ Query")
callback(true)
}
var versionedPlatDataSet = 0
for (p=0; p < platResultSet.length; p++){
(function(index){
var platform = platResultSet[index]
var options = createOptions(platform);
//Get Versions
var versionq = "\"version\",{\"platform\":" + platform + "}"
console.log("Versionq::"+versionq)
var dataSets = [];
//var versions = ["1.3.0", "1.3.2"]; // (select disctinct(version) from cpu where platform = plat)
// Use distinct() to find distinct Versions
db.collection("perfR").distinct(versionq,function(err, verResultSet){
if ( err ) throw err;
var maxVerCnt = verResultSet.length // 2
if (maxVerCnt == 0){
db.close()
console.log("Bad Versionq Query")
callback(true)
}
var dataSetResponseCnt = 0
for ( v=0; v < verResultSet.length; v++){
(function(idx){
var dataq = "{platform:" + platform + ",version:" + version + "},{filename:1,secs:1,_id:0}"
// Use find() to find filename and secs for given version and platform
db.collection("perfR").find(dataq,function(err, dataResultSet){
if ( err ) throw err;
if (dataResultSet.length == 0){
console.log("Bad dataq Query")
callback(true)
}
//do something with filename and secs
dataSetResponseCnt++
if (maxVerCnt == dataSetResponseCnt){
var platformData = {"options":options, "labels":labels, "datasets":dataSets, "platform":platform}
platformDataSets.push(platformData)
if (versionedPlatDataSet == maxPlatCnt){
db.close()
callback(null,platformDataSets)
}
}
})
})(v)
}
versionedPlatDataSet++
})(p)
}
}
}
At "1" I am able to retrive distinct platforms
But at "2" I get verResultSet.length to be zero.
Can someone point to me what is wrong?
(PS: This is my first serious async problem with javascript so bear with my code. All suggestions are welcome :) )
you can use Promises. so for example your code is going to be something like this:
return loadPlatforms().then(function (res){
res.map(function(platform){
loadVersion(platform).then(...)
}
})
Your use of .distinct() isn't correct. You are passing a JSON-like string when the API actually takes two separate arguments (not including the callback). So the real code should in fact just be more or less what you originally showed:
var query = { platform: 'win' };
db.collection('perfR').distinct('version', query, function(err, verResultSet) {
// ...
});
I m creating mobile web application using html5 and javascript.I m having two javascript files. AttributesDatabase.js and AttributeView.js.From AttributeView.js i m calling one function from AttributeDatabase.js in that i m executing one select query.Now the query result should go to AtttributeView.js.But the Websql transaction is asynchronous call that is what it is not returning proper result.Is there any way to handle the websql result.
Please help if any way there?
Edited
AttributeView.js
var AttributeDAOObj = new AttributeDAO();
AttributeDAOObj.GetAttributeList();
alert(AttributeDAOObj.GetAttributeList()); //This alert is coming as undefined.
AttributeDAO.js
this.GetAttributeList = function () {
var baseDAOObj = new BaseDAO();
var query = "SELECT AttributeName FROM LOGS";
// this.Successcalbackfromsrc = this.myInstance.Successcalback;
var parm = { 'query': query, 'Successcalback': this.myInstance.Successcalback };
baseDAOObj.executeSql(parm);
}
//To Create database and execute sql queries.
function BaseDAO() {
this.myInstance = this;
//Creating database
this.GetMobileWebDB = function () {
if (dbName == null) {
var dbName = 'ABC';
}
var objMobileWebDB = window.openDatabase(dbName, "1.0", dbName, 5 * 1024 * 1024);
return objMobileWebDB;
}
//Executing queries and getting result
this.executeSql = function (query) {
var objMobileWebDB = this.myInstance.GetMobileWebDB();
objMobileWebDB.transaction(function (transaction) {
//In this transaction i m returning the result.The result value is coming.
transaction.executeSql(query, [], function (transaction, result) { return result; }, this.Errorclback);
});
}
}
The problem is in you succes call back (like in the comment to your question, stated by DCoder)
function (transaction, result) { return result; }
this is returning where to?
So this is how to do it (or at least one way)
you can do for example:
function (transaction,result){
console.log("yes, I have some result, but this doesn't say anything, empty result gives also a result");
// so check if there is a result:
if (result != null && result.rows != null) {
if (result.rows.length == 0) {
// do something if there is no result
}else{
for ( var i = 0; i < result.rows.length; i++) {
var row = result.rows.item(i);
var id = result.rows.item(i).id; //supposing there is an id in your result
console.log('Yeah! row id = '+id);
}
}
}else{
// do something if there is no result
}
};
note the code above can be compacter, but this is how to understand it better.
another way is to put this function is a seperate piece of code, so you keep the sql statement more compact and readable. Like you call you error callback this can be in your function (with this. in front of it) or a completely seperate function.
Newbie question. Why is this JavaScript function returning undefined?
var redis = require("redis"), client = redis.createClient();
function generatePageUrl() {
var randomStr = randomInt.toString(32);
// Check whether this URL is already in our database;
client.smembers("url:" + randomStr, function (err, data ) {
if (data.length != 0) {
// URL already in use, try again
return getPageUrl();
}
return randomStr;
});
}
var page_url = generatePageUrl();
// add it to the database, etc
I guess it must be getting to the end and returning before it reaches the inside of client.smembers.
But I really need to check the contents of the Redis set before it returns: can I get it to return from inside the callback? If not, what can I do?
Also, advice on the way I've used this function recursively would be welcome - I'm not sure it's completely sensible :)
Thanks for helping out a newcomer.
You can't return from inside a callback. Do it like this:
var redis = require("redis"), client = redis.createClient();
function generatePageUrl(cb) {
var randomStr = randomInt.toString(32);
// Check whether this URL is already in our database;
client.smembers("url:" + randomStr, function (err, data ) {
if (data.length != 0) {
// URL already in use, try again
getPageUrl(cb);
}
cb(randomStr);
});
}
generatePageUrl(function(page_url){
// add it to the database, etc
});
If you don't like this style, you might want to consider streamlinejs - it makes you able to write your code like this:
var redis = require("redis"), client = redis.createClient();
function generatePageUrl(_) {
var randomStr = randomInt.toString(32);
// Check whether this URL is already in our database;
var data = client.smembers("url:" + randomStr, _);
if (data.length != 0) {
// URL already in use, try again
return getPageUrl(_);
}
return randomStr;
}
var page_url = generatePageUrl(_);
// add it to the database, etc