I would like to replace some text in a string with values from a database using pg-promise. As I have not used Promises before, I'm struggling with how to deal with it in the best way.
What I have tried so far doesn't work as I try to combine synchronous and asynchronous programming:
var uid = ...;
"Some string".replace(/\#\{([\w]*?)\}/gmi, function(m, c) {
var r = "";
db.one("SELECT a FROM ... WHERE x = $1 AND y = $2", [c, uid])
.then(function(data) {
r = data.a;
});
return r;
});
r is, unsurprisingly, an empty string. Is there a way to rewrite this block to "wait" for the values from the database?
What I try to do is, to replace placeholders in a message that is send to the user. So the above is part of a function called prepareMessage and I send the message to the user using socket.io so it looks something like this:
io.to(socket.id).emit('message', { text: prepareMessage(msg) });
After some reading and more thinking, I came up with a solution which I'd like to add if someone else has a similar problem.
(In addition to the question above, I had the additional complication that my message is an array of strings and that the order was to be kept.)
The key was to use tasks to send all queries to the DB as one package and wait for all results to return. This led to the following code:
// Sample data
var messages = ["String 1 with no placeholder.",
"String 2, #{placeholder1}, String 2.2.",
"String 3 with some more #{placeholder2}."];
// Collect all matches in array
var matches = [];
messages.forEach(function(text, index) {
const regex = /\#\{([\w]*?)\}/gmi;
var m;
do {
matches.push(regex.exec(text))
} while(m);
});
// Request data from the database
db.task(function(t) {
return t.batch(matches.map(function(m) {
return t.oneOrNone("SELECT ... FROM ... WHERE id = $1", [m[1]])
}));
})
.then(function(r) {
// Replace all occurrences of placeholders
r.forEach(function(p) {
messages = messages.map(function(t) { return t.replace("#{"+p.id+"}", p.replacement); });
});
// Send message to user
io.emit('text', messages)M
})
.catch(function(e) {
// ... error handling ...
});
Related
I need some advice on how to structure this function as at the moment it is not happening in the correct order due to node being asynchronous.
This is the flow I want to achieve; I don't need help with the code itself but with the order to achieve the end results and any suggestions on how to make it efficient
Node routes a GET request to my controller.
Controller reads a .csv file on local system and opens a read stream using fs module
Then use csv-parse module to convert that to an array line by line (many 100,000's of lines)
Start a try/catch block
With the current row from the csv, take a value and try to find it in a MongoDB
If found, take the ID and store the line from the CSV and this id as a foreign ID in a separate database
If not found, create an entry into the DB and take the new ID and then do 6.
Print out to terminal the row number being worked on (ideally at some point I would like to be able to send this value to the page and have it update like a progress bar as the rows are completed)
Here is a small part of the code structure that I am currently using;
const fs = require('fs');
const parse = require('csv-parse');
function addDataOne(req, id) {
const modelOneInstance = new InstanceOne({ ...code });
const resultOne = modelOneInstance.save();
return resultOne;
}
function addDataTwo(req, id) {
const modelTwoInstance = new InstanceTwo({ ...code });
const resultTwo = modelTwoInstance.save();
return resultTwo;
}
exports.add_data = (req, res) => {
const fileSys = 'public/data/';
const parsedData = [];
let i = 0;
fs.createReadStream(`${fileSys}${req.query.file}`)
.pipe(parse({}))
.on('data', (dataRow) => {
let RowObj = {
one: dataRow[0],
two: dataRow[1],
three: dataRow[2],
etc,
etc
};
try {
ModelOne.find(
{ propertyone: RowObj.one, propertytwo: RowObj.two },
'_id, foreign_id'
).exec((err, searchProp) => {
if (err) {
console.log(err);
} else {
if (searchProp.length > 1) {
console.log('too many returned from find function');
}
if (searchProp.length === 1) {
addDataOne(RowObj, searchProp[0]).then((result) => {
searchProp[0].foreign_id.push(result._id);
searchProp[0].save();
});
}
if (searchProp.length === 0) {
let resultAddProp = null;
addDataTwo(RowObj).then((result) => {
resultAddProp = result;
addDataOne(req, resultAddProp._id).then((result) => {
resultAddProp.foreign_id.push(result._id);
resultAddProp.save();
});
});
}
}
});
} catch (error) {
console.log(error);
}
i++;
let iString = i.toString();
process.stdout.clearLine();
process.stdout.cursorTo(0);
process.stdout.write(iString);
})
.on('end', () => {
res.send('added');
});
};
I have tried to make the functions use async/await but it seems to conflict with the fs.openReadStream or csv parse functionality, probably due to my inexperience and lack of correct use of code...
I appreciate that this is a long question about the fundamentals of the code but just some tips/advice/pointers on how to get this going would be appreciated. I had it working when the data was sent one at a time via a post request from postman but can't implement the next stage which is to read from the csv file which contains many records
First of all you can make the following checks into one query:
if (searchProp.length === 1) {
if (searchProp.length === 0) {
Use upsert option in mongodb findOneAndUpdate query to update or upsert.
Secondly don't do this in main thread. Use a queue mechanism it will be much more efficient.
Queue which I personally use is Bull Queue.
https://github.com/OptimalBits/bull#basic-usage
This also provides the functionality you need of showing progress.
Also regarding using Async Await with ReadStream, a lot of example can be found on net such as : https://humanwhocodes.com/snippets/2019/05/nodejs-read-stream-promise/
I have multiple HTTP requests in a nodejs app that each returns a word of a sentence. The replies will come at different times, so I'm saving them in a dictionary, with the key being the original sentence's word index. Problem is, when I access the request object, I only get the last one.
var completed_requests = 0;
sentence = req.query.sentence;
sentence = "sentence to be translated"
responses=[];
words = sentence.split(" ");
for(j=0;j<words.length;j++){
var word = words[j];
var data={
word:word
};
var options = {
url: 'example.com',
form:data,
index:j
};
request.post(options, function(err,httpResponse,body){
options = options;
if(!err){
responses.push({options.index: body});
completed_requests+=1;
if(completed_requests==words.length){
var a="";
for(var k=0;k<words.length;k++){
a+=responses[k]+" ";
}
res.render('pages/index', { something: a });
}
}
else{
//err
}
});
}
Basically, when I access the object.index object, the object returned isn't the one used for the original request, but the last one (for some reason). How should I resolve this?
When we take a look at how the code is evaluated by JavaScript due to it's async nature in node.js the problem becomes obvious:
For the first word the loop for(j=0;j<words.length;j++){ is executed.
The value of j is assigned to options.index. For the loop run this options.index has now the value 0.
request.post(options, function(err,httpResponse,body){ is executed but the callback handler will be invoked later.
For the first word the loop for(j=0;j<words.length;j++){ is executed.
The value of j is assigned to options.index. options.index has now the value 1.
request.post(options, function(err,httpResponse,body){ is executed but the callback handler will be invoked later.
The problem becomes obvious now since no new options objects are created but the value of j is assigned to options.index in every loop run. When the first callback handler is invoked options.index has the value words.length - 1.
To fix the problem we will wrap creating the options object in a function executeRequest
var completed_requests = 0;
sentence = req.query.sentence;
sentence = "sentence to be translated"
responses=[];
words = sentence.split(" ");
for(j=0;j<words.length;j++){
var word = words[j];
var data={
word:word
};
function executeRequest(url, form, index) {
var options = {
url: url,
form: form,
index: index
};
request.post(options, function(err,httpResponse,body){
// options = options; Superfluous
if(!err){
responses.push({ [index]: body});
completed_requests+=1;
if(completed_requests==words.length){
var a="";
for(var k=0;k<words.length;k++){
a+=responses[k]+" ";
}
res.render('pages/index', { something: a });
}
}
else{
//err
}
});
}
executeRequest('example.com', data, j);
}
A good read about scoping and hoisting in JavaScript can be found here http://www.adequatelygood.com/JavaScript-Scoping-and-Hoisting.html
You need to use an async routine such as forEach or map, also I suggest you read up on the async nature of node to help understand how to handle callbacks for io.
Dears ,
How can i run promises in nodejs sequentially , in the following example am looping through array of hours then for each fetched hour get result from the database , the issue here : am getting results but i want it sequentially same order that i got hours .
angular.forEach(SharedVar.getCategories(), function (h) {
t = h.split('-', 2);
t = t[0];
RESTApi.getAnswerdCallsByHour(t).then(function (answerdTotal) {
$scope.answerdCallsTotalByHour.push(answerdTotal);
var d = SharedVar.getDataS();
d[count] = answerdTotal;
SharedVar.setDataS(d);
count++;
});
});
Thanks ,
var promise = Promise.resolve(); // make an empty promise in the way you do it with your promise library
angular.forEach(SharedVar.getCategories(), function (h) {
promise.then(function() {
return RESTApi.getAnswerdCallsByHour(t).then(function (answerdTotal) {});
});
});
The way to do it sequently would be to do one Request and do the next request inside the promise.
I think the better approach by far is to extend your SharedVar.setDataS(d) function in a way, that it does not depend on getting the data sequentially. Like having a SharedVar.setDataS(d, index) and using the config var in your $http.get (or whatever) functioncall inside your RESTApi to promote that index all the way to the promise.
If your RESTApi looks like this:
var RESTApi = {
getAnswerdCallsByHour : function(hour) {
var url = "bla.com/myservice?hour=" + hour;
return $http.get(url).data;
}
// Some other Methods...
Then you need a way to pass something to "reorder" your Data when it arrives asynchronously, this could be a index you count up or in your case maybe the hour Variable:
var RESTApi = {
getAnswerdCallsByHour : function(hour) {
var url = "bla.com/myservice?hour=" + hour;
var config = [];
config.hour = hour;
return $http.get(url, config); // Return the promise not just data or a specific field
}
// Some other Methods...
Now when your promise is fullfiled you can access your "hour" Variable like so:
var d = SharedVar.getDataS();
d[promise.config.hour] = promise.data;
SharedVar.setDataS(d);
Now you know what piece of data correlates to which request and you do not need to recieve Data in order. The last piece only works properly when hours runs sequential from 0 to 23, if that isn't the case you need to:
var RESTApi = {
getAnswerdCallsByHour : function(hour, index) {
var url = "bla.com/myservice?hour=" + hour;
var config = [];
config.index = index;
return $http.get(url, config);
}
// Some other Methods...
...
...
var d = SharedVar.getDataS();
d[promise.config.index] = promise.data;
SharedVar.setDataS(d);
Safari's answer is how I typically handle this. (Sorry, I don't have enough rep to comment yet...) You were experiencing problems with it because the example provided does not capture and use the new promise in subsequent loops. See my comments on the slightly modified version here:
var promise = Promise.resolve();
angular.forEach(SharedVar.getCategories(), function (h) {
t = h.split('-', 2);
t = t[0];
// You must capture the new promise here; the next loop will wait
// for the promise returned from getAnswerdCallsByHour to resolve.
promise = promise.then(function() {
// Halt downstream promises until this returned promises finishes
return RESTApi.getAnswerdCallsByHour(t).then(function (answerdTotal) {
$scope.answerdCallsTotalByHour.push(answerdTotal);
var d = SharedVar.getDataS();
d[count] = answerdTotal;
SharedVar.setDataS(d);
count++;
});
});
});
Edit: I know JS is asynchronous, I have looked over the How to Return thread. The issue I'm having is that going from "foo" examples to something specific = I'm not quite sure where to re-format this.
Also here is some context: https://github.com/sharkwheels/beanballs/blob/master/bean-to-osc-two.js
I have a question about returns in node. It might be a dumb question, but here goes. I have a function that connects to a socket, and gets OSC messages from processing:
var sock = dgram.createSocket("udp4", function(msg, rinfo) {
try {
// get at all that info being sent out from Processing.
//console.log(osc.fromBuffer(msg));
var getMsg = osc.fromBuffer(msg);
var isMsg = getMsg.args[0].value;
var isName = getMsg.args[1].value;
var isAdd = getMsg.address;
var isType = getMsg.oscType;
// make an array out of it
var isAll = [];
isAll.push(isName);
isAll.push(isMsg);
isAll.push(isAdd);
isAll.push(isType);
// return the array
console.log(isAll);
return isAll;
} catch (error) {
console.log(error);
}
});
Below I have the start of another function, to write some of that array to a BLE device. It needs name and characteristics from a different function. How do I get the below function to use isAll AND two existing parameters?
var writeToChars = function (name, characteristics) { // this is passing values from the BLE setup function
// i need to get isAll to here.
// eventually this will write some values from isAll into a scratch bank.
}
Thanks.
async call in this case be written something like this. state can be maintained in the variables in closure if required. In this particular case - you can do without any state (isAll) as well.
var isAll;
var soc = dgram.createSocket('udp4', oncreatesocket);
function oncreatesocket(msg, rinfo)
{
isAll = parseMessage(msg);
writeData(isAll);
}
function parseMessage(msg) {
...
// code to parse msg and return isAll
}
function writeData() {}
if the writeData is small enough function. It can be inside oncreatesocket without impacting the readability of the code.
Alright. So I figured out what to do, at least in this scenario. I'm sure there is a better way to do this, but for now, this works.
I'm mapping an existing global array of peripherals into the write function, while passing the OSC message to it as a parameter. This solved my issue of "how do I get two pieces of information to the same place". It figures out which peripheral is which and writes a different value to each scratch bank of each peripheral accordingly. Leaving here for future reference.
var writeToBean = function(passThrough){
var passThrough = passThrough;
console.log("in Write to bean: ", passThrough);
_.map(beanArray, function(n){
if(n.advertisement.localName === passThrough.name){
//var name = n.advertisement.localName;
n.discoverSomeServicesAndCharacteristics(['a495ff20c5b14b44b5121370f02d74de'], [scratchThr], function(error, services, characteristics){
var service = services[0];
var characteristic = characteristics[0];
var toSend = passThrough.msg;
console.log("service", service);
console.log("characteristic", characteristic);
if (toSend != null) {
characteristic.write(new Buffer([toSend]), false, function(error) {
if (error) { console.log(error); }
console.log("wrote " + toSend + " to scratch bank 3");
});
}
// not sure how to make the program resume, it stops here. No error, just stops processing.
});
}
});
}
Hi I have a backbone web app using Jquery and NodeJs/mongo as the server side framework. I'm having problems with making a http get call with a foreah loop and the results of the get call being iteratively added to each row of the loop.
var eventid = this.model.get("_id");
var inPromise = $.get("/registrants/list?eventid="+eventid,null,null,"json").then(
function (result){
var temp;
var finalVal = '';
var tempfinalVal = "";
var loop = 0
percentage = 0;
$.each(result.registrants,function(index,registrant){
temp = JSON.parse(registrant.fields);
for (var key in temp) {
if(key =="Email"){
if(temp[key] != ""){
$.get("/stats/registrant?userid="+temp[key]+"&eventid="+eventid,null,null,"json").then(function(result2){
percentage = (result2.Stats.type ===undefined || result2.Stats.type ==null) ? "0": result2.Stats.type;
finalVal +=percentage+"\n";
}).fail(function(){
percentage = "0";
});
}
}else if(key =="eventid"){
loop++;
finalVal = finalVal.slice(0, - 1);
finalVal +='\n';
}
finalVal +=temp[key] + ',';
}
});
//promises.push(inPromise);
}
).done(function(finalVal){
$("#webcast-download-registrants-tn").attr("href",'data:text/csv;charset=utf-8;filename=registration.csv",'+encodeURIComponent(finalVal));
console.log("DONE");
}).fail(function(){
console.log("fail");
});
// promise.done(function () {
// console.log(" PROMISE DONE");
// });
So I have the loop through a collection and the last item of the docuemnt gets a content froma nother http call and when all is fone it will create a CSV file. The problem is that THE "DONE" text echos firts then the "CALL" text is displayed
Rick, your problem is not the simplest due to :
the need for nested asynchronous gets
the need to build each CSV data row partly synchronously, partly asynchronously.
the need for a mechanism to handle the fulfilment of multiple promises generated in the inner loop.
From what you've tried, I guess you already know that much.
One important thing to note is that you can't rely on for (var key in temp) to deliver properties in any particular order. Only arrays have order.
You might try something like this :
var url = "/stats/registrant",
data = { 'eventid': this.model.get('_id') },
rowTerminator = "\n",
fieldNames = ['firstname','lastname','email','company','score'];
function getScore(email) {
return $.get(url, $.extend({}, data, {'userid':email}), null, "json").then(function(res) {
return res.Stats ? res.Stats.type || 0 : 0;
}, function() {
//ajax failure - assume score == 0
return $.when(0);
});
}
$.get("/registrants/list", data, null, "json").then(function(result) {
var promises = [];//An array in which to accumulate promises of CSV rows
promises.push($.when(fieldNames)); //promise of CSV header row
if(result.registrants) {
$.each(result.registrants, function(index, registrant) {
if(registrant.fields) {
// Synchronously initialize row with firstname, lastname, email and company
// (omitting score for now).
var row = fieldNames.slice(0,-1).map(function(fieldName, i) {
return registrant.fields[fieldName] || '';
});
//`row` remains available to inner functions due to closure
var promise;
if(registrant.fields.Email) {
// Fetch the registrant's score ...
promise = getScore(registrant.fields.Email).then(function(score) {
//... and asynchronously push the score onto row
row.push(score);
return row;
});
} else {
//or synchronously push zero onto row ...
row.push(0);
//... and create a resolved promise
promise = $.when(row);
}
promises.push(promise);//Accumulate promises of CSV data rows (still in array form), in the correct order.
}
});
}
return $.when.apply(null, promises).then(function() {
//Join all the pieces, in nested arrays, together into one long string.
return [].slice.apply(arguments).map(function(row) {
return row.join(); //default glue is ','
}).join(rowTerminator);
});
}).done(function(str) {
$("#webcast-download-registrants-tn").attr("href",'data:text/csv;charset=utf-8;filename=registration.csv",'+encodeURIComponent(str));
console.log("DONE");
}).fail(function() {
console.log("fail");
});
partially tested
See comments in code for explanation and please ask if there's anything you don't follow.