Develop Reference

Return multiple values from stored procedure

The idea is that each subject has multiple topics, and when I call the function getTopicsForSubject() in order to get this data to a website page, it returns only 1 of the records from the table. I'm testing this using console.log(response) in the JavaScript file to see what is being passed in from the stored procedure/api connection. I'm thinking I need to read what's being passed by the stored procedure as if it were an array, although I'm not too sure how this is done.
Stored Procedure:
USE [Capstone]
GO
/****** Object: StoredProcedure [dbo].[getTopicsForSubject] Script Date: 2/21/2021 11:30:03 AM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE [dbo].[getTopicsForSubject]
#SubjectID int
AS
BEGIN
select *
from Topic
where SubjectID = #SubjectID
return;
END
API Code
private static string ExecuteSPGetSubjectsForTopic(string queryString, string subjectID)
{
string json = "";
string connectionString = ConfigurationManager.AppSettings["dbconn"].ToString();
using (SqlConnection conn = new SqlConnection(connectionString))
{
conn.Open();
// 1. create a command object identifying the stored procedure
SqlCommand cmd = new SqlCommand(queryString, conn);
// 2. set the command object so it knows to execute a stored procedure
cmd.CommandType = CommandType.StoredProcedure;
// 3. add parameter to command, which will be passed to the stored procedure
cmd.Parameters.Add(new SqlParameter("#SubjectID", subjectID));
// execute the command
using (SqlDataReader rdr = cmd.ExecuteReader())
{
// iterate through results, printing each to console
while (rdr.Read())
{
json = (string)rdr[0].ToString() + "|" + (string)rdr[1].ToString()+ "|" + (string)rdr[2].ToString() + "|" + (string)rdr[3].ToString();
}
}
}
return json;
}
JavaScript Code
function getTopicsForSubject()
{
var postObj = {
subjectID: localStorage.getItem('myFutureCurrentSubject')
};
console.log(postObj);
var req = new XMLHttpRequest();
req.open('POST', 'https://localhost:44303/api/JSON/getTopicsForSubject', true);
req.setRequestHeader('Content-Type', 'application/json');
req.onreadystatechange = function() { // Call a function when the state changes.
if (this.readyState === XMLHttpRequest.DONE && this.status === 200) {
console.log(req.response);
}
}
req.send(JSON.stringify(postObj));
return false;
}

You're reinitializing your JSON variable each time when reading a row. Try this:
json += (string)rdr[0].ToString() + "|" + (string)rdr[1].ToString()+ "|" + (string)rdr[2].ToString() + "|" + (string)rdr[3].ToString();
This is not the right way to return data. In JS you will still get this as a string and then parse it like this to get the actual values:
var array = req.response.split('|');
for (var i = 0; i < array.length; i++) {
console.log(array[i]);
}
I would suggest you use a proper way to handle this data by return an HTTP response from API instead of a string. E.g. create a list and then populate it while reading from the reader and return it. Try this:
List<object[]> topics = new List<object[]>();
while (rdr.Read())
{
object[] row = new object[rdr.FieldCount];
for (int i = 0; i < rdr.FieldCount; i++)
{
row[i] = rdr[i];
}
topics.Add(row);
}
return Ok(new { Data = topics });

Creating global VAR in functions

So I'm having trouble with getting a VAR in a function to be global, I have tried the following resources:
What is the scope of variables in JavaScript?
My previous question was marked as a duplicate but after reviewing the link above it did not help with my issue.
Here is my previous question:
So I'm using OpenTok to create a online conferencing tool and need to grab the session details from an API on a different server. I've created a php script on the other server that grabs session information based on the session id provided by a URL parameter. I know that the php script and most of the JavaScript is working correctly because when I console.log data from the parsed JSON it prints the correct information. However when I try to put the variables into the credentials area I get the following error:
ReferenceError: thesession is not defined
Here is the code used to get the JSON from a PHP script on a separate server:
var url_string = window.location.href;
var url = new URL(url_string);
var session = url.searchParams.get("s");
if (session == '') {
window.location.replace("http://www.google.com");
}
var getJSON = function(url, callback) {
var xhr = new XMLHttpRequest();
xhr.open('GET', url, true);
xhr.responseType = 'json';
xhr.onload = function() {
var status = xhr.status;
if (status === 200) {
callback(null, xhr.response);
} else {
callback(status, xhr.response);
}
};
xhr.send();
};
getJSON('http://192.168.64.2/api/meeting/?uid=' + session,
function(err, data) {
if (err !== null) {
console.log('Error');
}
var thesession = data.sessionID;
var thetoken = data.token;
console.log(thesession);
console.log(thetoken);
});
let otCore;
const options = {
credentials: {
apiKey: "####",
sessionId: thesession,
token: thetoken
},
And here is a screenshot of the console:
The top console log is "thesession" and the second console log is "thetoken". I have tried looking up the error but can't quite find one with the same usage as mine.
The desired outcome would be that I could using the data from the parsed JSON and use the result as the credentials e.g. data.sessionID which is bound the the VAR thesession.
I know this might be a scope issue, but I'm not sure how I could alter the code to make it work as intended.
Any help would be much appreciated, this one has really got me stumped :)
How would I alter the scope to get the desired function? I have reviewed the link that was given on the previous question, but this didn't help me with my issue.

var thesession = data.sessionID;
Is defined within its execution context, which is the callback function you've passed to getJSON.
One step in the right direction is to reverse the assignment. Assign 'thesession' to the options object within the scope where 'thesession' exists.
const options = {
credentials: {
apiKey: "####",
sessionId: null,
token: thetoken
}
};
getJSON('http://192.168.64.2/api/meeting/?uid=' + session,
function(err, data) {
if (err !== null) {
console.log('Error');
}
var thesession = data.sessionID;
var thetoken = data.token;
console.log(thesession);
console.log(thetoken);
options.credentials.sessionId = thesession;
});
However, it's important to realize that your program is not going to wait for this assignment. It will send the getJSON request, and then continue processing. Your options object won't have a sessionId until the getJSON call finishes and its callback has been invoked.
This would be a good opportunity to delve into Promises, which will help you better understand how to handle the non-blocking nature of javascript.

Your problem is that this line var thesession = data.sessionID is scoped within the function function(err, data) { ... }. In order to allow two functions to use the same variable, you need to make sure that the variable isn't declared somewhere they don't have access to.
It's the difference between this:
function func1() {
var x = 3
}
function func2() {
console.log(x)
}
func1();
func2();
and this:
var x;
function func1() {
x = 3
}
function func2() {
console.log(x)
}
func1();
func2();
Similarly, if you declare var thesession; at the start of your script (or at least outside that other function) then just set it with thesession = data.sessionID, your final part will have access to your variable thesession.
Edit
In context:
var url_string = window.location.href;
var url = new URL(url_string);
var session = url.searchParams.get("s");
var thesession;
var thetoken;
if (session == '') {
window.location.replace("http://www.google.com");
}
var getJSON = function(url, callback) {
var xhr = new XMLHttpRequest();
xhr.open('GET', url, true);
xhr.responseType = 'json';
xhr.onload = function() {
var status = xhr.status;
if (status === 200) {
callback(null, xhr.response);
} else {
callback(status, xhr.response);
}
};
xhr.send();
};
getJSON('http://192.168.64.2/api/meeting/?uid=' + session,
function(err, data) {
if (err !== null) {
console.log('Error');
}
thesession = data.sessionID;
thetoken = data.token;
console.log(thesession);
console.log(thetoken);
});
let otCore;
const options = {
credentials: {
apiKey: "####",
sessionId: thesession,
token: thetoken
},
As a side-note - I'd also recommend not using var and instead just using let of const, depending on if you want your variable to be mutable or not.

How can I retrieve plane text data from one local ip to another in javascript?

I am using an ESP32 Wifi module as a master to host a webpage displaying the values of a number of binary data points in a table as either OK or FAILED. I need to have this device retrieve data from another ESP32 client on a local IP i.e 192.168.138.50/readVal1 this address will display simply plane text either OK or FAILED. I would like to take this value and display it in the table produced by my master module. How should I go about doing this?
I have tried using an HTTP get request as follows in the Arduino code.
void runTest6(){
String payload;
HTTPClient http;
http.begin("192.168.137.50/readBatt1");
int httpCode = http.GET();
if(httpCode > 0) {
payload = http.getString();
Serial.println(payload);
}else{
Serial.println("HTTP request error");
}
http.end();
String batt6val = payload;
server.send(200, "text/plane", batt6val);
}
Here is my Javascript on the root that handles the updates\
function getData(){
try{
console.log("Getting Data...");
for(var i = 1;i<=NUMOFUNITS;i++){
(function (i){
setTimeout(function () {
console.log("(debug msg)in loop #: " + i)
var xhttp = new XMLHttpRequest();
var current = "batt" + i + "val";
var dataRead = "readBatt" + i;
xhttp.onreadystatechange = function(){
if (this.readyState == 4 && this.status == 200){
console.log("updating innerHTML for data value: " + i);
document.getElementById(current).innerHTML = this.responseText;
}else if(this.readyState == 4 && this.status == 404){
console.log("no battery # " + i);
document.getElementById(current).innerHTML = "None found";
}
};
xhttp.open("GET", dataRead, true);
xhttp.send();
if(i == 1){
updateTime();
console.log("Updated times.")
}
}, 400*i);
})(i);
};
console.log("Data update complete.");
}
catch(err){
alert(err.name);
throw err;
getData(); //try to get data again
}
finally{
console.log("DONE");
}
}

Using and HTTP server I am able to send the information between ESP32's. Using the WebServer I have set server.on("/status/{}", sendData); where the {} hold the pathArg aka a number representing which data is being asked for. The function senData() takes the pathArg and sends the appropriate data as follows.
void sendData(){
String battString = server.pathArg(0);
Serial.println("Sending Data... PathArg= " + battString);
int battNum = battString.toInt();
int arrayNum = battNum - 1;
server.send(200, "text/plane", battStatus[arrayNum]);
}
Here an array called battStatus holds the status of each.

How to keep multiple requests separate in Nodejs / Expressjs

I am developing a NodeJS / ExpressJS application on my computer. I have node running locally. I have a single page web app. When it needs information it makes ajax requests with jQuery.
The problem is when I have multiple requests for different sets of data.
Node/express will start processing the first request and then the second request comes in before the first request has been fulfilled, it sends the response to the second request from the first request instead of sending it to the first request like it is suppose to. If I put a pause ( using an alert ) in my app so that is slows it down so the next request doesn't get sent until the first request was fulfilled, everything works fine.
I don't understand why this is happening. I thought node / express was suppose to be able to handle this and keep the requests separate.
Also, I get a "Can't set headers after they are sent" error in node because it is apparently merging the requests....
Here is what happens
ajax request 1 -> server
ajax request 2 -> server
ajax request 3 -> server
server -> request1 ( no response )
server -> request2 ( request 1's data)
server -> request3 ( request 2's data)
server for request3 --> error: header's already sent
I am using Google Chrome 63 with jQuery 3.3.1 on a Windows 10 machine running Node 8.9.4 and Express 4.16.2
My work-around is to chain the ajax requests so that each request doesn't get called until the prior request has received a response from the server. But I shouldn't have to do that...
Here is the relevant server code:
var mysql = require("mysql");
var express = require('express');
var app = express();
var DEBUG = true;
var request = null;
var response = null;
var currentDataRowParser = null;
var con = mysql.createConnection(config);
function ParseMySqlRowData(rowData)
{
if (DEBUG) console.log("ParseMySqlRowData");
return JSON.stringify(rowData);
}
var ParseMySqlRowsDatatoResponse = function (err, rows)
{
if (DEBUG) console.log("ParseMySqlRowsDatatoResponse");
var MySQLRows;
try
{
if (!err)
{
MySQLRows = "[";
for (var i = 0; i < rows.length; i++)
{
if (i > 0)
MySQLRows += ", ";
MySQLRows += currentDataRowParser(rows[i]);
}
MySQLRows += "]";
if (DEBUG) console.log("write rows");
if (DEBUG) console.log(MySQLRows);
response.send(MySQLRows);
response.end();
}
}
catch (ex)
{
if (DEBUG) console.log("ParseMySQLRowsDatatoResponse: ERROR");
if (DEBUG) console.log(ex);
}
};
var GetQueryData = function (query, dataRowParser, parseDataCallbackFunction)
{
if (DEBUG) console.log("GetQueryData");
currentDataRowParser = dataRowParser;
if (parseDataCallbackFunction == null || parseDataCallbackFunction == undefined)
parseDataCallbackFunction = ParseDataCallback;
try
{
if (DEBUGQUERY)
{
console.log("before query");
console.log(con.query(query, parseDataCallbackFunction));
console.log("after query");
console.log(query.sql);
DEBUGQUERY = false;
}
else
{
con.query(query, parseDataCallbackFunction);
}
}
catch (ex)
{
console.log(ex);
}
};
app.post('/getdata', function(req, res)
{
request = req;
response = res;
var query;
switch (request.body.loaddata)
{
case "dataset1":
query = "SELECT * FROM table1 WHERE key='" + request.body.key + "'";
GetQueryData(query,ParseMySqlRowData,ParseMySqlRowsDatatoResponse);
break;
case "dataset2":
query = "SELECT * FROM table2 WHERE key='" + request.body.key + "'";
GetQueryData(query,ParseMySqlRowData,ParseMySqlRowsDatatoResponse);
break;
case "dataset3":
query = "SELECT * FROM table3 WHERE key='" + request.body.key + "'";
GetQueryData(query,ParseMySqlRowData,ParseMySqlRowsDatatoResponse);
break;
}
};

You cannot store req and res in global or module-level variables. When a second request comes in, it will immediately overwrite your globals and it will mix up the data for the various requests.
Does't node separate each request instance?
Yes, there is a separate request instance, but not a separate global or module-level namespace. So, when you assign the req into the global space, you are overwriting the previous one and your code will then use the wrong one.
It is very helpful to have the request and response as a global variable. Otherwise I would have to be passing them all over the place.
You HAVE to pass them to lower level functions that need them. That's how you keep each request separate from the others. ANY function that needs to operate on req or res should be passed those variables so it knows exactly which ones to operate on.
node.js has a shared global and module-level namespace. So, all requests in flight at the same time use that same namespace. The ONLY data that should ever be stored there is data that you specifically want to be shared between requests (such as session state, for example). Individual request or response objects should never be stored in a shared variable.
A more common way to code your type of code is to call a function like your GetQueryData() and have it return the data (likely via a promise) and then you send the response in the original request handler. Then, you don't have to pass req or res down multiple levels at all. Your helper functions just fetch data. The request handlers fetch data, then send the response. It's often a better encapsulation of functionality.
Here's one way to restructure your code along the lines described above.
GetQueryData() returns a promise that fulfills with the data
ParseMySqlRowsData() just returns a parsed result or null if a parsing error
app.post() just gets the data (via a promise) and then sends the appropriate response.
There's no global req or res and there's no need to pass them anywhere.
Here's the code:
var mysql = require("mysql");
var express = require('express');
var app = express();
var DEBUG = true;
var currentDataRowParser = null;
var con = mysql.createConnection(config);
function ParseMySqlRowData(rowData) {
if (DEBUG) console.log("ParseMySqlRowData");
return JSON.stringify(rowData);
}
var ParseMySqlRowsData = function(err, rows) {
if (DEBUG) console.log("ParseMySqlRowsDatatoResponse");
var MySQLRows;
try {
if (!err) {
MySQLRows = "[";
for (var i = 0; i < rows.length; i++) {
if (i > 0)
MySQLRows += ", ";
MySQLRows += currentDataRowParser(rows[i]);
}
MySQLRows += "]";
if (DEBUG) console.log("write rows");
if (DEBUG) console.log(MySQLRows);
return MySQLRows;
}
} catch (ex) {
if (DEBUG) console.log("ParseMySQLRowsDatatoResponse: ERROR");
if (DEBUG) console.log(ex);
return null;
}
};
var GetQueryData = function(query, dataRowParser, parseDataCallbackFunction) {
return new Promise((resolve, reject) =>{
if (DEBUG) console.log("GetQueryData");
let currentDataRowParser = dataRowParser;
if (parseDataCallbackFunction == null || parseDataCallbackFunction == undefined)
parseDataCallbackFunction = ParseDataCallback;
try {
if (DEBUGQUERY) {
console.log("before query");
console.log(con.query(query, parseDataCallbackFunction));
console.log("after query");
console.log(query.sql);
DEBUGQUERY = false;
} else {
con.query(query, function(err, rows) {
if (err) {
reject(err);
} else {
let result = parseDataCallbackFunction(rows);
if (result) {
resolve(result);
} else {
reject(new Error("ParseMySqlRowsData error"));
}
}
});
}
} catch (ex) {
console.log(ex);
reject(new Error("GetQueryData error"));
}
});
};
app.post('/getdata', function(req, res) {
var query;
let p;
switch (request.body.loaddata) {
case "dataset1":
query = "SELECT * FROM table1 WHERE key='" + request.body.key + "'";
p = GetQueryData(query, ParseMySqlRowData, ParseMySqlRowsData);
break;
case "dataset2":
query = "SELECT * FROM table2 WHERE key='" + request.body.key + "'";
p = GetQueryData(query, ParseMySqlRowData, ParseMySqlRowsData);
break;
case "dataset3":
query = "SELECT * FROM table3 WHERE key='" + request.body.key + "'";
p = GetQueryData(query, ParseMySqlRowData, ParseMySqlRowsData);
break;
default:
p = Promise.reject(new Error("Invalid request.body.loaddata"));
break;
}
p.then(data => {
res.send(data);
}).catch(err => {
console.log(err);
res.sendStatus(500);
});
};
P.S. I see you still have a module-level variable you should not have: currentDataRowParser. That needs to be replaced by passing the appropriate parser to ParseMySqlRowsData() as an argument, not using a module-level shared variable. I will leave that as an excercise for you to fix. Shared variables for operating on a specific request state are a bad idea in ANY server programming and specifically in node.js programming. Keep your request-specific state in your function arguments or on the req or res object itself. That's how you prevent overwritting the data from one request with the data from another while they are being processed.

NodeJs Assertion failed on HTTP call (Mac)

var client = require('http');
var endpoint = apiEndpoint;
var request = client.get(endpoint, function(responseFromApi) {
var responseString = '';
responseFromApi.setEncoding('utf-8');
responseFromApi.on('data', function(data) {
responseString += data;
});
// To reformat the string response into Json...
responseFromApi.on('end', function() {
var jsonResponse = JSON.parse(responseString);
callback(jsonResponse);
});
});
I am making API calls using the method above, however on random instances my call fails due to the Assertion fail like below. Anyone has any idea how to fix this?
Assertion failed: (handle->type == UV_TCP || handle->type == UV_TTY || handle->type == UV_NAMED_PIPE), function uv___stream_fd, file ../deps/uv/src/unix/stream.c, line 1568.
Environment: Mac, Nodejs
Note: I have tested the same code on an AWS lambda server and never faced this issue. I am guessing this is a Mac only instance. Lord Google informed me that it is a Mac desync issue.
Same is true if trying to get data from a dynamoDB sitting on Amazon server using the code below...
// To get userID.
var userId = getUserIdFromContext(this);
if (!userId) {
callback('userId is not set.');
}
// To get table name.
var table = constants.dynamoDBTableName;
if(!table) {
callback('DynamoDB Table name is not set.');
}
// To set the DocumentClient.
if(!doc) {
doc = new aws.DynamoDB.DocumentClient({apiVersion: '2012-08-10'});
}
// To set the params.
var params = {
Key: {
CustomerId: userId
},
TableName: table,
ConsistentRead: true
};
// To get data from table.
var skillContext = this;
doc.get(params, function(err, data){
if(err) {
console.log('get error: ' + JSON.stringify(err, null, 4));
callback(err);
} else {
if(isEmptyObject(data)) {
callback('The object is empty.');
} else {
var userData = JSON.parse(data.Item['Data']);
extractUserData(skillContext, userData, callback);
}
}
});
}