I have been trying to retrieve the data using the MongoJS driver for node.js.The Code which I am using is as follows
req.on('end', function(){
var decodedBody = querystring.parse(fullBody);
story=decodedBody.name;
var z=new Array();
console.log(story);
res.writeHead(200,{'Content-Type': 'text/html'});
res.write('<html><body>');
db.frames.find({str_id:story}).toArray(function(err,doc){
console.log(doc);
for(var t=0;t<doc.length;t++)
{
var picid=doc[t].pic_id;
console.log(picid);
db.pictures.find({_id:picid}).toArray(function(err,pic){
res.write('<img src="'+pic[0].name+'"/>');
});
}
})
res.end('</body></html>');
});
The problem here is that because of the asynchronous nature of the code the response gets ends first and then the code inside the block of database gets executed and because of that nothing gets displayed on the browser i.e an image in this case .Thankx in advance.
Don't fight the asynchronous nature of node.js, embrace it!
So you should fire off all your requests, marking each one as completed when the response arrives. When all requests are completed, render your images and body/html closing tags.
I don't usually work with node.js, so I can make some mistakes, but it may look like this:
res.write('<html><body>');
db.frames.find({str_id:story}).toArray(function(err,doc){
console.log(doc);
var completed = {};
for(var t = 0; t < doc.length; t++) {
var picid = doc[t].pic_id;
completed.picid = false;
console.log(picid);
db.pictures.find({_id: picid}).toArray(function(err, pic) {
// mark request as completed
completed.picid = pic;
// check if all requests completed
var all_finished = true;
for(var k in completed) {
if(completed[k] === false) {
all_finished = false;
break;
}
}
// render final markup
if(all_finished) {
for(var k in completed) {
var pic = completed[k];
res.write('<img src="'+pic[0].name+'"/>');
}
res.end('</body></html>);
}
});
}
})
just put the res.end('</body></html>'); inside your db.frames.find function. Check when you reached doc.length - 1 and then send the end command.
Related
I'm a beginner at node js and I'm doing a simple project with pure node.js.
So here is my code:
if(req.url ==="/"&&req.method==="POST"){
let reqBody = "";
req.on('data', chunk=>{
reqBody += chunk.toString();
});
req.on("end", ()=>{
reqBody = reqBody.split("&");
for(let i=0; i<reqBody.length; i++){
reqBody[i]=reqBody[i].split("=");
reqBody[i] = reqBody[i][1];
};
//filter country
let countryFound;
if(reqBody[1].length>0){
let countryList = "";
let countryVal = [];
countryListStream = fs.createReadStream("./public/country.list.json", "UTF-8");
countryListStream.on("data", countryChunk=>{
countryList+=countryChunk;
countryChunk = JSON.parse(countryChunk);
countryFound = countryChunk.filter(elem=> elem["name"].toLowerCase()==reqBody[1].toLowerCase());
if(countryFound.length!==0){
countryListStream.destroy();
};
});
countryListStream.on("end", ()=>{
countryFound = "Not Found"
});
};
});
};
My problem is below "filter country" comment:
when I log the "countryFound" variable outside of the events of "countryListStream", it displays undefined.But when i log it inside of the events, it displays what I want. I think it's becaus of how node.js is made, but I don't know to continue my code if it's undefined.
I think that I need to include a code that waits until the variable is updated, and then it runs the rest.
I tried with this after the if statement, and it didn't fixed it:
if(countryFound!===undefined){
console.log(countryFound);
}
From looking at the documentation, calling countryStream.destroy() emits close and error events. So, it would make sense to add a handler to the close event where you can continue processing the values that you have assigned to those variables:
countryStream.on('close', () => {
console.log(countryFound) // should not be undefined now
// ...do something with your new values
});
I have a list of 125,000 + Id numbers.
I am making a request to an api to get more information for each one.
But my problem is that the api will stop giving me a response if I request more then 6 per second.
I need a way to control the speed of the requests.
Just use a function called by setInterval to do the actual API querying ?
Simple example:
var ids = [ /* big array here */ ];
function queryAllIds(ids, callback) {
var processedIds = [];
var lastProcessedId = 0;
var processedIdCount = 0;
var intervalId;
function queryApi() {
var idToProcess = lastProcessedId++;
doActualQuery(ids[idToProcess], function(result) {
processedIds[idToProcess] = result;
processedIdCount++;
if (processedIdCount === ids.length) {
nextTick(callback, processedIds);
}
});
}
if (intervalId && lastProcessedId === ids.length)
clearInterval(intervalId);
}
intervalId = setInterval(queryApi, 1000/6);
}
queryAllIds(ids, function (processedIds) {
// Do stuff here
});
We ended up using rate limiter which provided the rate limiting we needed right out of the box. https://www.npmjs.com/package/limiter
Or quite possibly I am doing it wrong, in fact, more than likely I am doing it wrong.
Have a table which contains a "tree" of skill, starting at the root level and may be as deep as ten levels (only two so far), but I want to return it as one big fat JSON structure, so I want to ask the database for each set of data, build my structure then ask for the next level.
Of course if I just send of my requests using mongoose, they will come back at any time, as they are all nice asyncronous calls. Normally a good things.
Looking at the documentation for Mongoose(using 4.1.1) it seems like it has a promise built in, but whenever I try to use it the api call throws a hissy fit and I get a 500 back.
Here is my simple function:
exports.getSkills = function(req,res) {
console.log("Will return tree of all skills");
for (var i = 0; i<10; i++){
var returnData = [];
console.log("Lets get level " + i );
var query = Skill.find({level: i });//The query function
var promise = query.exec; //The promise?
promise.then(function(doc) { //Totally blows up at this point
console.log("Something came back")
return "OK";
});
}
}
The Mongoose documentation on the subject can be found here
http://mongoosejs.com/docs/api.html#promise_Promise
var promise = query.exec;
// =>
var promise = query.exec()
exports.getSkills = function(req,res) {
console.log("Will return tree of all skills");
var p;
for (var i = 0; i < 10; i ++) {
if (i == 0 ) {
p = Skill.find({level:i}).exec();
} else {
p.then(function (){
return Skill.find({level:i}).exec()
})
}
p.then(function (data) {
//deal with your data
})
}
p.then(function () {
// deal with response
})
}
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.
I am newbie to nodejs.It's very hard to handle callbacks at nodejs level. I have code like this,
getItems(request,function(jsonObject){
var itemData={};
var itemDetails=new Array();
for(var i=0;i < jsonObject.length;i++){
getItemDetails(jsonObject[i].value.item_id,function(jsonObject){
itemDetails.push(jsonObject);
});
}
itemData["itemDetails"]=itemDetails;
response.contentType("application/json");
response.send({"data":itemData});
});
while executing the above code, the for loop is continuing with out getting callback from getItemDetails method and response sent to client. My requirement is the loop will wait until getting the call back from the getItemDetails then response should send.
I have tried with process.nextTick(), but i am unable to find where i have to use that process.nextTick().. Please anybody provide suggestions.
Thanks in advance.
You need to send the response only after you get all the items, so modify your code like so:
getItems(request,function(jsonObject) {
var itemData = {},
itemDetails = [],
itemsLeft = len = jsonObject.length,
i;
function sendResponse(itemDetails) {
itemData["itemDetails"] = itemDetails;
response.contentType("application/json");
response.send({ "data": itemData });
}
for (i = 0; i < len; i++) {
getItemDetails(jsonObject[i].value.item_id, function(jsonObject) {
itemDetails.push(jsonObject);
// send response after all callbacks have been executed
if (!--itemsLeft) {
sendResponse(itemDetails);
}
});
}
});
Note: I've used itemLeft here since it's a more generic way to solve these kind of problems, but Ianzz approach is also ok since you can compare the length of the two arrays.
You can't get the loop to wait, but you can modify your code to get the behavior you are expecting:
getItems(request,function(outerJsonObject){
var itemData={};
var itemDetails=new Array();
for(var i=0;i < outerJsonObject.length;i++){
getItemDetails(jsonObject[i].value.item_id,function(innerJsonObject){
itemDetails.push(innerJsonObject);
if (itemDetails.length == outerJsonObject.length) {
// got all item details
itemData["itemDetails"]=itemDetails;
response.contentType("application/json");
response.send({"data":itemData});
}
});
}
});