i am quiet new to java script and node js.
i have a problem with a simple function that i call, and it gets done more than one time.
this is my code
app.post('/checkGetSensorIds', function (req, res) {
var tables=['temperature', 'pressure', 'linear_acceleration'];
var ids= [1];
DButils.checkAllSensorsForId(connection, 1 , tables , function(idHasSensorsInfo){
console.log("idHasSensorsInfo is: \n" , idHasSensorsInfo);
});
res.end();
});
/*this function gets a user Id, and the table of all sensors the customer wants, and return true if this
user id has information in all the sesnsor tables that were requested, otherwise returns false*/
exports.checkAllSensorsForId= function(dbConnection, id , sensorsTables, callback){
var sensorsTablesLength= sensorsTables.length;
for (var i = 0; i < sensorsTables.length; i++) {
var tableName= sensorsTables[i];
DButils.checkSingleSensorForId(dbConnection, id, tableName, function(idHasSensorInfo){
if(idHasSensorInfo == false){
callback(false);
return;
}
//in case user have all info in db, we get here and need to return false
if(i == sensorsTablesLength){
callback(true);
return;
}
});
}
};
/*this function gets a user Id, and a single sensor table, and returns true if the user has information
in the requested sensor table, otherwise returns false*/
exports.checkSingleSensorForId= function(dbConnection , id , sensorTable, callback){
var myQuery = 'SELECT count(*) as IdCount FROM ' + sensorTable + ' WHERE id= ' + id;
var query = dbConnection.query(myQuery, function (err, row, result) {
console.log(query.sql);
if (err) {
console.log("checkSingleSensorForId error");
console.error(err);
return;
}
var count= row[0].IdCount;
var idHasSensorInfo = (count > 0);
callback(idHasSensorInfo);
});
};
console.log("idHasSensorsInfo is: \n" , idHasSensorsInfo); is a line that invoked 3 times, while should be only once.
someone has any idea why, and what i need to do to fix it?
You have this line:
DButils.checkAllSensorsForId(connection, 1 , tables , function(idHasSensorsInfo){
console.log("idHasSensorsInfo is: \n" , idHasSensorsInfo);
});
Then you have this:
exports.checkAllSensorsForId= function(dbConnection, id , sensorsTables, callback){
...
for (var i = 0; i < sensorsTables.length; i++) {
...
callback();
...
}
};
So the callback line will be invoked as many times as you call it, which in your case is probably 3 - all it does is call the function from above, so thats why you see it invoked 3 times.
I'm not sure exactly what you are trying to do, but if the callback should be only called once, make sure its ran only once - if it should 'cancel' the for - add a condition to the for or use a promise to resolve whenever you are ready.
Related
I wrote some code that checks a list, and checks if each item in the list is present in the other one. If the item isn't found, it adds it to the database.
The scanning code is correct (the part that says db.scan) but somewhere towards the end the code isn't going through because its not executing the console.log part (Where it says "Entering journal into database..." title of article"
When I execute this code, nothing happens. At least there are no errors... but its not even logging the console.log parts so something is wrong.
// accessing the database
function DatabaseTime(sourcesDates, timeAdded, links, titles, descriptions) {
sourcesDates = sourcesDates;
links = links;
titles = titles; // this will be used to check on our articles
descriptions = descriptions;
var autoParams;
var databaseOperation = function (sourcesDates, timeAdded, links, titles, descriptions) {
var scanParams = { TableName: "Rnews" }
// using code to setup for accessing the 2nd list
db.scan(scanParams, function(err, scanData) { // scanData = the 2nd list we are going to work with
var counter = 0; // just a way to help make my code more accurate as seen later in the loops
var counter2 = 0;
// this is the first list iterating on
for (var i = 0; i < links.length; i++) {
counter = 0;
// looping through items in second list
for (var x = 0; x < scanData.Items.length; x++) {
// if article is not in db
if (titles[i] !== scanData.Items[x].title) {
continue;
}
else if (titles[i] === scanData.Items[x].title) {
// intention is to immediately move to the next item in the first list if this block executes
console.log("Article found: \"" + titles[i] + "\". Not proceeding anymore with article.");
counter++;
break;
} else {
// if this article isnt found anywhere in the list we are checking on, add to database
if (x === scanData.Items.length && counter !== 0) {
autoParams = {
TableName: "Rnews",
Item: {
title: titles[i],
source: sourcesDates[i],
url: links[i],
description: descriptions[i],
lastAddOrUpdated: dbTimeStamp,
timePublish: timeAdded[i]
}
}
console.log("Entering journal to database: " + titles[i]);
db.put(autoParams, function(err, data) {
if(err) throw err;
});
//}
}
}
}
}
});
//console.log("Complete");
};
databaseOperation(sourcesDates, timeAdded, links, titles, descriptions);
}
//// END
You never called the function DatabaseTime. Your code just declares the function and does nothing else. In order for the function to execute, you must invoke it.
Is any possible to increment var licznik in this block of code?
I try sth like this, But always receives 0. Could someone explain me what I'm doing wrong?
rows.forEach(function(record) {
var licznik = 0;
var offer = manager.createOffer('76561198252553560');
inventory.forEach(function(item) {
if(licznik <= record.amount) {
if(item.market_hash_name == record.real_name) {
var asid = item.assetid;
(function(licznik){
connection.query('SELECT count(id) as wynik FROM used where asset_id = \'' + asid + '\'', function(err, wiersze) {
if (wiersze[0].wynik == 0) {
var employee = {
asset_id: asid,
trans_id: record.tid
};
connection.query('INSERT INTO used SET ?', employee, function(err, res) {
if (err) throw err;
offer.addMyItem(item);
console.log(licznik);
&licznik++;
});
}
});
})(licznik);
}
}
});
});
As the comment on your original question points out, I have no context for what this code is actually trying to accomplish. What I can tell you is that your callbacks supplied to connection.query are NOT fired on each iteration of the forEach. The whole reason connection.query takes a callback is because you don't know when the operation will complete. Node is designed to be asynchronous so all it does on each iteration of the forEach loop is begin the query. The callback supplied to the query could be invoked at any time which also means that a query that fired after another query could potentially fire its callback before the callback from the first query. It just depends on how long each query takes.
If you need licznik to be incremented on every iteration of the forEach then you need to increment it after your if statement.
rows.forEach(function(record) {
var licznik = 0;
var offer = manager.createOffer('76561198252553560');
inventory.forEach(function(item) {
if(licznik <= record.amount) {
// .... omitted for brevity
}
licznik++; // <-- increment here, outside of the closure.
});
});
Again, I have zero clue what you're actually trying to do with that variable so this may not solve your real problem, but that's the way to get it to increment in that loop.
PS - You may not be understanding that you actually have two licznik variables here. You create a new one when you wrap all your logic in a closure function like you did. If you change the variable declared at the top of your closure function you'll see that it's not the same variable as the one outside the closure function.
rows.forEach(function(record) {
var licznik = 0;
var offer = manager.createOffer('76561198252553560');
inventory.forEach(function(item) {
if(licznik <= record.amount) {
if(item.market_hash_name == record.real_name) {
var asid = item.assetid;
(function(licznik2) { // <-- notice this is a new variable
connection.query('SELECT count(id) as wynik FROM used where asset_id = \'' + asid + '\'', function(err, wiersze) {
if (wiersze[0].wynik == 0) {
var employee = {
asset_id: asid,
trans_id: record.tid
};
connection.query('INSERT INTO used SET ?', employee, function(err, res) {
if (err) throw err;
offer.addMyItem(item);
console.log(licznik2);
licznik2++;
});
}
});
})(licznik);
}
}
});
});
I want use mysql function's variable to the outside in node.js. I'm doing two queries. But I can't access the variable. I've used global variable but result is the same. How do I get access to the variable?
My codes seems like:
// Mysql query...
mysql.query(messages_query, function(err, result) {
// Add the results in socket...
if(result.length > 0) {
// messages array
var messages = [];
// Foreach
result.forEach(function(message){
// User query...
var user_query = 'SELECT id, username, avatar FROM users WHERE id = '+message["from"];
// Second mysql query...
mysql.query(user_query, function(err, result) {
// Add result to global function
if(result.length > 0) global.user += result;
else console.log("User not found");
});
// Message array
message["from"] = global.user;
// Concat...
var messages = messages.concat(message);
});
console.log("--- MESSSAGES ---");
console.log(messages);
// Users are undefined
} else console.log("User not found");
});
ps. sorry but my bad english
So we've got a number of problems or misunderstandings here. First of all, these two lines are conflicting one another:
var messages = [];
var messages = messages.concat(message);
at a minimum the second line should be:
messages.push(message);
to add a message to the array. However, a more fundamental issue is the misunderstanding that your code is synchronous. The following calls are asynchronous:
mysql.query...
result.forEach...
mysql.query...
You've got the first one right, but the other two are likely misused. It is my opinion that you're actually looking for something like this:
// Mysql query...
mysql.query(messages_query, function(err, result) {
// Add the results in socket...
if(result.length > 0) {
// messages array
var messages = [];
// Foreach
for (int i = 0; i < result.length; i++) {
// User query...
var user_query = 'SELECT id, username, avatar FROM users WHERE id = ' + result[i].from;
// Second mysql query...
mysql.query(user_query, function(err, userResult) {
// Add result to global function
if(userResult.length > 0) {
result[i].from = userResult.username;
messages.push(result[i]);
}
else {
console.log("User not found");
}
});
}
console.log(messages);
}
else {
console.log("User not found");
}
});
NOTE: while the above probably works, it is my greatest position that you just need to change the messages_query to JOIN to the users table and get the fields you want back in the messages_query. Doing this will mean you don't have the transpose the results.
I have a function in my express app that makes multiple queries within a For Loop and I need to design a callback that responds with JSON when the loop is finished. But, I'm not sure how to do this in Node yet. Here is what I have so far, but it's not yet working...
exports.contacts_create = function(req, res) {
var contacts = req.body;
(function(res, contacts) {
for (var property in contacts) { // for each contact, save to db
if( !isNaN(property) ) {
contact = contacts[property];
var newContact = new Contact(contact);
newContact.user = req.user.id
newContact.save(function(err) {
if (err) { console.log(err) };
}); // .save
}; // if !isNAN
}; // for
self.response();
})(); // function
}; // contacts_create
exports.response = function(req, res, success) {
res.json('finished');
};
There are a few problems with your code besides just the callback structure.
var contacts = req.body;
(function(res, contacts) {
...
})(); // function
^ you are redefining contacts and res in the parameter list, but not passing in any arguments, so inside your function res and contacts will be undefined.
Also, not sure where your self variable is coming from, but maybe you defined that elsewhere.
As to the callback structure, you're looking for something like this (assuming contacts is an Array):
exports.contacts_create = function(req, res) {
var contacts = req.body;
var iterator = function (i) {
if (i >= contacts.length) {
res.json('finished'); // or call self.response() or whatever
return;
}
contact = contacts[i];
var newContact = new Contact(contact);
newContact.user = req.user.id
newContact.save(function(err) {
if (err)
console.log(err); //if this is really a failure, you should call response here and return
iterator(i + 1); //re-call this function with the next index
});
};
iterator(0); //start the async "for" loop
};
However, you may want to consider performing your database saves in parallel. Something like this:
var savesPending = contacts.length;
var saveCallback = function (i, err) {
if (err)
console.log('Saving contact ' + i + ' failed.');
if (--savesPending === 0)
res.json('finished');
};
for (var i in contacts) {
...
newContact.save(saveCallback.bind(null, i));
}
This way you don't have to wait for each save to complete before starting the next round-trip to the database.
If you're unfamiliar with why I used saveCallback.bind(null, i), it's basically so the callback can know which contact failed in the event of an error. See Function.prototype.bind if you need a reference.
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.