I am using node.js and created a module to fetch data from the sql server database. The data is retreived as JSON.
Here is the code
b.js
var mssql = require('mssql');
var config = {
user: 'sa',
password: 'scott',
server: 'MSSQL2008',
database: 'AdventureWorks',
stream: false
};
var msconnection = new mssql.Connection(config, function (err) {
if (err) console.log(err);
});
module.exports.getCustomersDetails = function (callback, id) {
var request = new mssql.Request(msconnection);
//Add Parameters to the SP
if (id != null) {
request.input('ID', id);
}
request.execute('CUSTOMER_DETAILS_GET', function (err, recordsets, returnValue) { // get data
if (err) console.log(err);
responseContent = {
recordDataKey: 'data',
data: recordsets[0]
};
callback(responseContent);
});
};
a.js
var c = require('./b.js');
c.getCustomersDetails(function (responsecontent) {
console.log(responsecontent);
}, '101,202,303,505,808, 100, 200, 300, 400');
When I run a.js the console shows nothing and that's because there are lot of records in the table.
Can anybody suggest how can I get all the records? Any help would be much appreciated.
Edit: I have 25 columns in one row so it is bringing me top 140 records but when I write get me top 150 or all in SP then it does not show anything in the console.
Update:
can anybody help me and suggest how we can do streaming in this case?
Asynchronicity is back to bite you!
var c = require('./b.js');
// start loading the db
// it's not ready yet when you call the function!
c.getCustomersDetails(function (responsecontent) {
console.log(responsecontent);
}, '101,202,303,505,808, 100, 200, 300, 400');
You'll need to rewrite your module to use an initialization function and callback. I would do something like:
c.init(function(){
c.getCustomersDetails(); // ...
});
and
var msconnection;
exports.init = function(callback){
msconnection = new mssql.Connection(config, function (err) {
if (err) console.log(err);
callback();
});
};
Related
I have a node.js file that subscribes to a topic and upon receiving a published message scans a local mysql db for the most recent entry in a variable named "command". Command values will trigger various responses, but I have left this portion out since my issue is before this.
My mysql query appears to be giving me errors. I am trying to look for the most recent entry of the command column and assign the value to a var command. I thought this code would do the trick:
var sql = 'SELECT command FROM motoron2 ORDER BY id DESC LIMIT 1';
con.query(sql, function (err, result) {
if (err) throw err;
});
console.log(result);
var command = result[1];
console.log(command);
But I am getting the following response which seems to indicate an error in the mysql query:
user#server.domain [bin]# node motorlistener.js
Connected to MYSQL!
Connected to Broker!
{"pulse":1}
1
/home/user/etc/domain/bin/motorlistener.js:62
console.log(result);
^
ReferenceError: result is not defined
at MqttClient.<anonymous> (/home/user/etc/domain/bin/motorlistener.js:62:17)
at MqttClient.emit (events.js:314:20)
at MqttClient._handlePublish (/home/user/node_modules/mqtt/lib/client.js:1277:12)
at MqttClient._handlePacket (/home/user/node_modules/mqtt/lib/client.js:410:12)
at work (/home/user/node_modules/mqtt/lib/client.js:321:12)
at Writable.writable._write (/home/user/node_modules/mqtt/lib/client.js:335:5)
at doWrite (/home/user/node_modules/readable-stream/lib/_stream_writable.js:409:139)
at writeOrBuffer (/home/user/node_modules/readable-stream/lib/_stream_writable.js:398:5)
at Writable.write (/home/user/node_modules/readable-stream/lib/_stream_writable.js:307:11)
at TLSSocket.ondata (_stream_readable.js:718:22)
The full code is below, but does anyone know what is causing this error?
////////////////////////////////////////////////////////////////////////////////
//setup
var mqtt = require('mqtt'); //for client use
const fs = require('fs');
var caFile = fs.readFileSync("/home/user/etc/domain/bin/ca.crt");
var topic = "heartbeat";
var mysql = require('mysql');
var con = mysql.createConnection({
host : 'localhost',
user : 'myuser',
password : 'mypass',
database : 'mydb'
});
var options={
port:8883,
clientId:"yo",
username:"myuser2",
password:"mypassw",
protocol: 'mqtts',
clean:true,
rejectUnauthorized: false,
retain:false,
ca:caFile
};
var client = mqtt.connect("http://dns.org",options);
//mqtt connection dialog
client.on("connect",function(){
console.log("Connected to Broker!");
client.subscribe(topic, {qos:1});
});
//mqtt connection handle errors
client.on("error",function(error){
console.log("Broker Connection Error");
process.exit(1);
});
//database connection
con.connect(function(err) {
if (err) throw err;
console.log("Connected to MYSQL!");
});
//handle incoming messages from broker
client.on('message',function(topic, message, packet){
var raw = ""+message;
console.log(raw);
var obj = JSON.parse(raw);
var pulse = obj.pulse;
console.log(pulse);
var sql = 'SELECT command FROM motoron2 ORDER BY id DESC LIMIT 1';
con.query(sql, function (err, result) {
if (err) throw err;
});
console.log(result);
var command = result[1];
console.log(command);
if (command == 1) {
console.log("command=1");
}
else {
console.log("command not equal to 0");
}
});
I am getting the following response which seems to indicate an error in the mysql query
That's not an error in your MySQL query. It's a null reference error because you're trying to use result outside the callback.
Changing your code to this will work:
var sql = 'SELECT command FROM motoron2 ORDER BY id DESC LIMIT 1';
con.query(sql, function (err, result) {
if (err) {
throw err;
}
// access result inside the callback
console.log(result);
var command = result[0];
console.log(command);
});
Depending on your environment you may be able to re-write your code using promises and async/await to reduce the nested scopes.
To do so, you'd need to turn your callback into a promise and then you can await it, like so:
let sql = 'SELECT command FROM motoron2 ORDER BY id DESC LIMIT 1';
// 1 -- we turn the query into a promise
const queryPromise = new Promise((resolve, reject) => {
con.query(sql, function (queryError, queryResult) {
if (queryError) {
reject(queryError);
}
resolve(queryResult);
});
});
try {
// 2 -- we can now await the promise; note the await
let result = await queryPromise;
// 3 -- now we can use the result as if it executed synchronously
console.log(result);
let command = result[0];
console.log(command);
} catch(err) {
// we can catch query errors and handle them here
}
Putting it all together, you should be able to change the on message event handler to an async function in order to take advantage of the async/await pattern as shown above:
client.on('message', async function(topic, message, packet) {
/* .. you can use await here .. */
});
All above code from #Mike Dinescu works perfectly fine. Just dont forget on the end to close the connection!
Else the runner will hangs after tests have finished.
the full solution:
async function mySqlConnect(dbquery) {
const conn = mysql.createPool({
host: 'localhost',
port: 3306,
user: 'test',
password: 'test',
database: 'test'
}, { debug: true });
// 1 -- we turn the query into a promise
const queryPromise = new Promise((resolve, reject) => {
conn.query(dbquery, function (queryError, queryResult) {
if (queryError) {
reject(queryError);
}
resolve(queryResult);
});
});
try {
// 2 -- we can now await the promise; note the await
let result = await queryPromise;
// 3 -- now we can use the result as if it executed synchronously
//console.log(result);
let command = await result[0];
//console.log(command);
return command;
} catch(err) {
}
finally{
conn.end(function(err) {
if (err) {
return console.log('error:' + err.message);
}
//console.log('Close the database connection.');
});
}
}
I'm trying to write a JSON object (or string, unsure) to my mysql database using node.js. I first retrieved the JSON via an xml url using xml2js. I am able to log the json string result in my console via JSON.stringify, but I am unsure how to proceed from here.
Here is the url I took the xml from: https://water.weather.gov/ahps2/hydrograph_to_xml.php?gage=deld1&output=xml
I would like to write each instance from the JSON string to a row, with the columns as the name of the data. It would look something like this:
Here is my code in index.js, which I enact with node index.js on the console:
var parseString = require('xml2js').parseString;
var http = require('http');
var https = require('https');
var mysql = require('mysql');
var con = mysql.createConnection({
host: "localhost",
user: "root",
password: "password",
database: "mydb"
});
function xmlToJson(url, callback) {
var req = https.get(url, function(res) {
var xml = '';
res.on('data', function(chunk) {
xml += chunk;
});
res.on('error', function(e) {
callback(e, null);
});
res.on('timeout', function(e) {
callback(e, null);
});
res.on('end', function() {
parseString(xml, function(err, result) {
callback(null, result);
});
});
});
}
var url = "https://water.weather.gov/ahps2/hydrograph_to_xml.php?gage=deld1&output=xml"
xmlToJson(url, function(err, data) {
if (err) {
return console.err(err);
}
strungout = JSON.stringify(data, null, 1);
console.log(strungout);
//strungout contains my json string
})
con.connect(function(err) {
if (err) throw err;
//below is where I might make an insert statement to insert my values into a mysql table
var sql = someinsertstatement
con.query(sql, function (err, result) {
if (err) throw err;
console.log("records inserted");
res.end();
});
});
As mentioned, when I run the above code in my console, the console returns the JSON, though I am unsure how to assign this to a variable that I can then write into my mysql database.
Alternatively, if there is an easier way to write xml from a website directly to my mysql database, I would certainly appreciate any pointers. I feel like it should be easier than this, but I am new to pretty much all of it.
EDIT:
Adding the JSON. I removed the line breaks to consolidate it. Trying to assign the result '4.68' to a variable.
data = {"site": {"observed": [{"datum": [{"valid": [{"_": "2019-02-21T19:42:00-00:00","$": {"timezone": "UTC"}}],"primary": [{"_": "4.68","$": {"name": "Stage","units": "ft"}}]}]}]}};
Thank you.
This worked on my end. Found that the main data you seek is site.observed.datum
const parser = require('xml2json');
const request = require("request");
var mysql = require('mysql');
var con = mysql.createConnection({
host: "localhost",
user: "root",
password: "password",
database: "mydb"
});
var api_url = 'https://water.weather.gov/ahps2/hydrograph_to_xml.php?gage=deld1&output=xml';
function xmlToJson(url, callback){
return request({
method: 'GET',
url: api_url,
}, function (error, response, body) {
if (error) {
return callback({
errorResponse: error,
rowsToInsert: false
});
}else{
let jsonRes = JSON.parse(parser.toJson(body));
let datumResult = jsonRes.site.observed.datum;//I had to log Object.keys multple time to get the
const readyForDB = datumResult.map(x => {
let timeOfReading = x.valid.$t;
let stage = x.primary.$t;
let flow = x.secondary.$t;
return [
timeOfReading, stage, flow
]
});
return callback({
errorResponse: false,
rowsToInsert: readyForDB
});
}
})
}
return xmlToJson(api_url, ({errorResponse, rowsToInsert}) => {
if(errorResponse){
throw callback.errorResponse;
}
return con.connect(function(err) {
if (err) throw err;
//below is where I might make an insert statement to insert my values into a mysql table
var sql = "INSERT INTO forecast (timeOfReading, stage, flow) VALUES ?"
con.query(sql, [rowsToInsert], function (err, result) {
if (err) throw err;
console.log(result.affectedRows + " rows inserted");
});
});
});
Sounds like you have the JSON you want but are unsure how to access data within it. Correct me if I'm wrong.
Lets say you have this JSON object called "test":
{
a:1
b:{
x:2
}
}
You can access the value of 1 by calling test.a, and similarly access the value of 2 by calling test.b.x
I'm trying to introduce the simplest caching layer in my webapp, all I want to do is cache the results from a few queries for 24 hours as that is how often the DB receieves new data. I'm trying to use node-cache-manager (which looks great) but struggling! I don't think I completely understand how it should be implemented into sequelize. The example is using Mongoose and Mongo by the looks of it:
function responder(res) {
return function respond(err, data) {
var startTime = moment(res.req._startTime);
var diff = moment().diff(startTime, 'ms');
if (err) {
err.status = 500;
res.render('error', {error: err});
} else {
data.requestTime = diff;
res.render('users/show', data);
}
};
}
function fetchUser(id, cb) {
var cacheKey = 'user_' + id;
memoryCache.wrap(cacheKey, function (cacheCb) {
console.log("Fetching user from slow database");
User.get(id, cacheCb);
}, cb);
}
router.get('/:id', function (req, res) {
fetchUser(req.param('id'), responder(res));
});
I'm using MySQL and currently have the example below, but I can see the query hitting the database every time, it does not seem to be persisting or creating the cache...:
function responder(res) {
return function respond(err, data) {
var startTime = moment(res.req._startTime);
var diff = moment().diff(startTime, 'ms');
if (err) {
err.status = 500;
res.json({valuesCount: err});
} else {
data.requestTime = diff;
res.json({valuesCount: res});
}
};
}
function fetchCount(req, cb) {
var cacheKey = 'allDatabaseRecords',
table = sequelize.import('extracts');
memoryCache.wrap(cacheKey, function (cacheCb) {
console.log("Fetching count from slow database");
table.count().then(cacheCb);
}, cb);
}
router.post('/extract-tool/data-filter', function(req, res) {
var table = sequelize.import('extracts');
fetchCount(req, responder(res));
});
I've tried following the documentation and the example, but this as mentioned, this still hits the DB every time! Any help is MASSIVELY appreciated!!!
I could not get this to work as per the examples given, I had to specifically set and get the key value pair to and from the cache each time.
Now it works fine, structured as below:
memoryCache.get(cacheKey, function(err, result) {
if (result !== undefined){res.json({billingAddress12LastName: result});}
});
memoryCache.wrap(cacheKey, function (cacheCb) {
console.log("Fetching count from slow database");
table.count().then(data);
memoryCache.set(cacheKey, data, {ttl: ttl}, function(err) {
res.json({valuesCount: data});
});
}, cb);
Still don't understand how the wrap function works and what its for as I'm explicitly setting and getting the cache values now, would appreciate some comments still :).
I am working on a crawler that stores the retrieved and parsed data into my MySQL DB.
Storing the results works pretty well, but I am stuck when it comes to end the connection.
I am using request, cheerio, async and mysql:
// DB params
var con = mysql.createConnection({
host: "localhost",
user: "user",
password: "password",
database: "mydatabase",
});
// Open connection to DB
con.connect(function(err) {
if (err) {
console.log('Error connecting to Db');
return;
}
console.log('Connection established');
});
// Array of Cities to crawl
var cities = ["olten", "zurich"];
// Todays Date
var today = new Date();
...
today = dd + '.' + mm + '.' + yyyy;
// Search every city
async.each(cities, function(item, callback){
// The Page to crawl
var page = "https://www.thepageto.com/search_xhr?fn=" + /*cities[i]*/ item + "&tn=&db=" + today + "&sort=trip_date&order";
console.log("Visiting page " + page);
request(page, function(error, response, body) {
if (error) {console.log("Error: " + error);}
// Check status code (200 is HTTP OK)
console.log("Status code: " + response.statusCode);
if (response.statusCode === 200) {
// Parse JSON
var data = JSON.parse(body);
// Use only result > html code
var content = data.html.results;
// Parse html
var $ = cheerio.load(content);
// Iterate through offers & Extract information & Store in a Object
$('.trip.relative').each(function() {
// Empty Object, has the same structure as the Db table
var json = {id: "", driver: "", rating: "", date: "", time: "", start: "", stops: "", end: "", price: "", url: "", query: ""};
// Assigning values
json.driver = $(this).find('.username').text();
...
// Save filled object in Db
save(json, callback);
});
}
});
}, function(err){
if (err) {
console.log('could not save');
} else {
console.log('lets end connection');
con.end(function(err) {if (err) throw err;});
}
}
);
function save(item, callback) {
con.query('INSERT INTO offers SET ?', item, callback);
}
The problem is, that the DB connection is ended before anything could be stored into the DB. The con.end() is always fired before the actual query or before the query completed. I have the intension that the save function has to return something when its done. If i run the script without the con.end(), the data is stored into the DB perfectly.
I am new to Node so I am still learning and hopefully you can help me with this.
Edit:
I now get an:
ReferenceError: callback is not defined
at save (/home/juki/crawler/crawler.js:143:46)
As well as an:
Error: Callback was already called.
at Query._callback (/home/juki/crawler/node_modules/async/dist/async.js:839: 36)
It looks like you do not call callback from your crawler.
You also do not seem to wait for save to finish. Try to rework save function, so it takes callback too. Something like:
function save(item, callback) {
con.query('INSERT INTO offers SET ?', item, callback);
}
And then call it like:
save(json, callback);
where callback is the one you get from async.each.
I have a python background and is currently migrating to node.js. I have problem adjusting to node.js due to its asynchronous nature.
For example, I am trying to return a value from a MySQL function.
function getLastRecord(name)
{
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"WHERE (name = ?) " +
"LIMIT 1 ";
var query_var = [name];
var query = connection.query(query_str, query_var, function (err, rows, fields) {
//if (err) throw err;
if (err) {
//throw err;
console.log(err);
logger.info(err);
}
else {
//console.log(rows);
return rows;
}
}); //var query = connection.query(query_str, function (err, rows, fields) {
}
var rows = getLastRecord('name_record');
console.log(rows);
After some reading up, I realize the above code cannot work and I need to return a promise due to node.js's asynchronous nature. I cannot write node.js code like python. How do I convert getLastRecord() to return a promise and how do I handle the returned value?
In fact, what I want to do is something like this;
if (getLastRecord() > 20)
{
console.log("action");
}
How can this be done in node.js in a readable way?
I would like to see how promises can be implemented in this case using bluebird.
This is gonna be a little scattered, forgive me.
First, assuming this code uses the mysql driver API correctly, here's one way you could wrap it to work with a native promise:
function getLastRecord(name)
{
return new Promise(function(resolve, reject) {
// The Promise constructor should catch any errors thrown on
// this tick. Alternately, try/catch and reject(err) on catch.
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"WHERE (name = ?) " +
"LIMIT 1 ";
var query_var = [name];
connection.query(query_str, query_var, function (err, rows, fields) {
// Call reject on error states,
// call resolve with results
if (err) {
return reject(err);
}
resolve(rows);
});
});
}
getLastRecord('name_record').then(function(rows) {
// now you have your rows, you can see if there are <20 of them
}).catch((err) => setImmediate(() => { throw err; })); // Throw async to escape the promise chain
So one thing: You still have callbacks. Callbacks are just functions that you hand to something to call at some point in the future with arguments of its choosing. So the function arguments in xs.map(fn), the (err, result) functions seen in node and the promise result and error handlers are all callbacks. This is somewhat confused by people referring to a specific kind of callback as "callbacks," the ones of (err, result) used in node core in what's called "continuation-passing style", sometimes called "nodebacks" by people that don't really like them.
For now, at least (async/await is coming eventually), you're pretty much stuck with callbacks, regardless of whether you adopt promises or not.
Also, I'll note that promises aren't immediately, obviously helpful here, as you still have a callback. Promises only really shine when you combine them with Promise.all and promise accumulators a la Array.prototype.reduce. But they do shine sometimes, and they are worth learning.
I have modified your code to use Q(NPM module) promises.
I Assumed your 'getLastRecord()' function that you specified in above snippet works correctly.
You can refer following link to get hold of Q module
Click here : Q documentation
var q = require('q');
function getLastRecord(name)
{
var deferred = q.defer(); // Use Q
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"WHERE (name = ?) " +
"LIMIT 1 ";
var query_var = [name];
var query = connection.query(query_str, query_var, function (err, rows, fields) {
//if (err) throw err;
if (err) {
//throw err;
deferred.reject(err);
}
else {
//console.log(rows);
deferred.resolve(rows);
}
}); //var query = connection.query(query_str, function (err, rows, fields) {
return deferred.promise;
}
// Call the method like this
getLastRecord('name_record')
.then(function(rows){
// This function get called, when success
console.log(rows);
},function(error){
// This function get called, when error
console.log(error);
});
I am new to Node.js and promises. I was searching for a while for something that will meet my needs and this is what I ended up using after combining several examples I found. I wanted the ability to acquire connection per query and release it right after the query finishes (querySql), or to get a connection from pool and use it within Promise.using scope, or release it whenever I would like it (getSqlConnection).
Using this method you can concat several queries one after another without nesting them.
db.js
var mysql = require('mysql');
var Promise = require("bluebird");
Promise.promisifyAll(mysql);
Promise.promisifyAll(require("mysql/lib/Connection").prototype);
Promise.promisifyAll(require("mysql/lib/Pool").prototype);
var pool = mysql.createPool({
host: 'my_aws_host',
port: '3306',
user: 'my_user',
password: 'my_password',
database: 'db_name'
});
function getSqlConnection() {
return pool.getConnectionAsync().disposer(function (connection) {
console.log("Releasing connection back to pool")
connection.release();
});
}
function querySql (query, params) {
return Promise.using(getSqlConnection(), function (connection) {
console.log("Got connection from pool");
if (typeof params !== 'undefined'){
return connection.queryAsync(query, params);
} else {
return connection.queryAsync(query);
}
});
};
module.exports = {
getSqlConnection : getSqlConnection,
querySql : querySql
};
usage_route.js
var express = require('express');
var router = express.Router();
var dateFormat = require('dateformat');
var db = require('../my_modules/db');
var getSqlConnection = db.getSqlConnection;
var querySql = db.querySql;
var Promise = require("bluebird");
function retrieveUser(token) {
var userQuery = "select id, email from users where token = ?";
return querySql(userQuery, [token])
.then(function(rows){
if (rows.length == 0) {
return Promise.reject("did not find user");
}
var user = rows[0];
return user;
});
}
router.post('/', function (req, res, next) {
Promise.resolve().then(function () {
return retrieveUser(req.body.token);
})
.then(function (user){
email = user.email;
res.status(200).json({ "code": 0, "message": "success", "email": email});
})
.catch(function (err) {
console.error("got error: " + err);
if (err instanceof Error) {
res.status(400).send("General error");
} else {
res.status(200).json({ "code": 1000, "message": err });
}
});
});
module.exports = router;
I am still a bit new to node, so maybe I missed something let me know how it works out. Instead of triggering async node just forces it on you, so you have to think ahead and plan it.
const mysql = require('mysql');
const db = mysql.createConnection({
host: 'localhost',
user: 'user', password: 'password',
database: 'database',
});
db.connect((err) => {
// you should probably add reject instead of throwing error
// reject(new Error());
if(err){throw err;}
console.log('Mysql: Connected');
});
db.promise = (sql) => {
return new Promise((resolve, reject) => {
db.query(sql, (err, result) => {
if(err){reject(new Error());}
else{resolve(result);}
});
});
};
Here I am using the mysql module like normal, but instead I created a new function to handle the promise ahead of time, by adding it to the db const. (you see this as "connection" in a lot of node examples.
Now lets call a mysql query using the promise.
db.promise("SELECT * FROM users WHERE username='john doe' LIMIT 1;")
.then((result)=>{
console.log(result);
}).catch((err)=>{
console.log(err);
});
What I have found this useful for is when you need to do a second query based on the first query.
db.promise("SELECT * FROM users WHERE username='john doe' LIMIT 1;")
.then((result)=>{
console.log(result);
var sql = "SELECT * FROM friends WHERE username='";
sql = result[0];
sql = "';"
return db.promise(sql);
}).then((result)=>{
console.log(result);
}).catch((err)=>{
console.log(err);
});
You should actually use the mysql variables, but this should at least give you an example of using promises with mysql module.
Also with above you can still continue to use the db.query the normal way anytime within these promises, they just work like normal.
Hope this helps with the triangle of death.
You don't need to use promises, you can use a callback function, something like that:
function getLastRecord(name, next)
{
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"LIMIT 1 ";
var query_var = [name];
var query = connection.query(query_str, query_var, function (err, rows, fields) {
//if (err) throw err;
if (err) {
//throw err;
console.log(err);
logger.info(err);
next(err);
}
else {
//console.log(rows);
next(null, rows);
}
}); //var query = connection.query(query_str, function (err, rows, fields) {
}
getLastRecord('name_record', function(err, data) {
if(err) {
// handle the error
} else {
// handle your data
}
});
Using the package promise-mysql the logic would be to chain promises using then(function(response){your code})
and
catch(function(response){your code}) to catch errors from the "then" blocks preceeding the catch block.
Following this logic, you will pass query results in objects or arrays using return at the end of the block. The return will help passing the query results to the next block. Then, the result will be found in the function argument (here it is test1). Using this logic you can chain several MySql queries and the code that is required to manipulate the result and do whatever you want.
the Connection object is created to be global because every object and variable created in every block are only local. Don't forget that you can chain more "then" blocks.
var config = {
host : 'host',
user : 'user',
password : 'pass',
database : 'database',
};
var mysql = require('promise-mysql');
var connection;
let thename =""; // which can also be an argument if you embed this code in a function
mysql.createConnection(config
).then(function(conn){
connection = conn;
let test = connection.query('select name from records WHERE name=? LIMIT 1',[thename]);
return test;
}).then(function(test1){
console.log("test1"+JSON.stringify(test1)); // result of previous block
var result = connection.query('select * from users'); // A second query if you want
connection.end();
connection = {};
return result;
}).catch(function(error){
if (connection && connection.end) connection.end();
//logs out the error from the previous block (if there is any issue add a second catch behind this one)
console.log(error);
});
To answer your initial question: How can this be done in node.js in a readable way?
There is a library called co, which gives you the possibility to write async code in a synchronous workflow. Just have a look and npm install co.
The problem you face very often with that approach, is, that you do not get Promise back from all the libraries you like to use. So you have either wrap it yourself (see answer from #Joshua Holbrook) or look for a wrapper (for example: npm install mysql-promise)
(Btw: its on the roadmap for ES7 to have native support for this type of workflow with the keywords async await, but its not yet in node: node feature list.)
This can be achieved quite simply, for example with bluebird, as you asked:
var Promise = require('bluebird');
function getLastRecord(name)
{
return new Promise(function(resolve, reject){
var connection = getMySQL_connection();
var query_str =
"SELECT name, " +
"FROM records " +
"WHERE (name = ?) " +
"LIMIT 1 ";
var query_var = [name];
var query = connection.query(query_str, query_var, function (err, rows, fields) {
//if (err) throw err;
if (err) {
//throw err;
console.log(err);
logger.info(err);
reject(err);
}
else {
resolve(rows);
//console.log(rows);
}
}); //var query = connection.query(query_str, function (err, rows, fields) {
});
}
getLastRecord('name_record')
.then(function(rows){
if (rows > 20) {
console.log("action");
}
})
.error(function(e){console.log("Error handler " + e)})
.catch(function(e){console.log("Catch handler " + e)});
May be helpful for others, extending #Dillon Burnett answer
Using async/await and params
db.promise = (sql, params) => {
return new Promise((resolve, reject) => {
db.query(sql,params, (err, result) => {
if(err){reject(new Error());}
else{resolve(result);}
});
});
};
module.exports = db;
async connection(){
const result = await db.promise("SELECT * FROM users WHERE username=?",[username]);
return result;
}