I am trying to write the results of a MongoDB query to a file using the native Node.js driver. My code is the following (based on this post: Writing files in Node.js):
var query = require('./queries.js');
var fs = require('fs');
var MongoClient = require('mongodb').MongoClient;
MongoClient.connect("mongodb://localhost:27017/test", function(err, db) {
if(err) { return console.dir(err); }
var buildsColl = db.collection('blah');
collection.aggregate(query.test, function(err, result) {
var JSONResult = JSON.stringify(result);
//console.log(JSONResult);
fs.writeFile("test.json", JSONResult, function(err) {
if(err) {
console.log(err);
} else {
console.log("The file was saved!");
}
});
});
collection.aggregate(query.next, function(err, result) {
var JSONResult = JSON.stringify(result);
//console.log(JSONResult);
db.close();
});
});
The file is written, but the contents are 'undefined.' Printing the result to the console works though.
Your code is not checking the err on the aggregate callback.
You are likely getting an Mongo error and the result is undefined in that case...
Other thing I could suspect is that you are getting multiple callbacks -- each one of them creates a new files, erasing the content.
Try using fs.appendFile instead of fs.writeFile and see if you are getting the expected data (plus the unwanted undefined)
For anyone stumbling across this the solution on where to put the db.close() is below:
collection.aggregate(query.test, function(err, result) {
var JSONResult = JSON.stringify(result);
//console.log(JSONResult);
fs.writeFile("test.json", JSONResult, function(err) {
if(err) {
console.log(err);
} else {
console.log("The file was saved!");
}
});
collection.aggregate(query.next, function(err, result) {
var JSONResult = JSON.stringify(result);
//console.log(JSONResult);
db.close();
});
});
Related
I have a collection with content:
db.simplecollection2.find()
{ "_id" : ObjectId("5c312200508c979b46d21866"), "artistname" : "The
Tea Party" }
When I change artistname with the following in mongo shell it works
db.simplecollection2.update(
{"_id":ObjectId("5c312200508c979b46d21866")},{"artistname":"new"})
However in javascript I get an Error: SyntaxError: Unexpected token O in JSON at position 7 at JSON.parse (), although I parse a string to object and not object to object.. why is that?
MongoClient.connect(url, function(err, db) {
if (err) throw err;
var dbo = db.db("simpledb");
var myquery = JSON.parse("{\"_id\":ObjectId(\"5c31184bdb14729aa4806882\")}");
var newvalues = { $set: {"artistname":"cool"} };
dbo.collection("simplecollection2").updateOne(myquery, newvalues, function(err, res) {
if (err) throw err;
console.log("1 document updated");
db.close();
});
Update using ObjectID():
let id = new mongo.ObjectID("5c312200508c979b46d21866");
db.simplecollection2.update({ "_id" : id }, { "artistname" : "new" });
Read More
The line where you call JSON.parse fails because the argument is not a JSON. If you do JSON.stringify({"_id":ObjectId("5c312200508c979b46d21866")}) you'll see that it can't turn that into a string either. The reason being that JSONs can contain strings, booleans, numbers, and arrays. ObjectId("5c312200508c979b46d21866") doesn't resolve to something the browser knows, even though it makes sense in the shell. However, I think if you pass it as a string, it should work as a query for the db.
MongoClient.connect(url, function(err, db) {
if (err) throw err;
var dbo = db.db("simpledb");
var myqueryObj = {
_id: 'ObjectId("5c312200508c979b46d21866")'
};
var myquery = JSON.parse(JSON.stringify(myqueryObj));
var newvalues = { $set: {"artistname":"cool"} };
dbo.collection("simplecollection2").updateOne(myquery, newvalues, function(err, res) {
if (err) throw err;
console.log("1 document updated");
db.close();
});
I am using protractor cucumber framework.I need to write some data into a file and read that data also.But it is not working as expected.The code i have tried is given below.
const fs = require('fs');
After(function(){
var content = ["kerala","asam"];
var str=content.toString();
var content1 = ["india","usa","uk"];
var str1=content1.toString();
if(str){
fs.writeFile('test.txt', str, (err) => {
if (err) {
console.error(err);
return
}
});
}
if(str1){
fs.writeFile('test.txt', str1, (err) => {
if (err) {
console.error(err);
return
}
});
}
});
AfterAll(function(callback){
console.log("afterall");
fs.readFile('test.txt', 'utf-8', function(err, buf) {
console.log(buf.toString());
});
callback();
});
some time the arrays may be empty(depending on the test execution).so if the array having data, i need to write that data into a file and read also.But the after writing into the file the, the file having data as given below
india,usa,uk
it should be
kerala,asam
india,usa,uk
How can i do this .Thanks in advance.
I am using NodeJs and MongoDb as a back-end service.In my collection i have several documents having fields named _id and Name but Node is returning only first document and showing error in console.I want to fetch only Name field of a document.
Error:
Here is my code:
var express = require('express');
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/";
var bodyParser = require('body-parser');
var app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended:true}));
app.post('/offers',(req, res) => {
MongoClient.connect(url, (err, db) => {
if(err) throw err;
var dbo = db.db('Tiffino_db');
dbo.collection("Offers")
.find({},{ projection: { _id: 0 } })
.toArray((err, result) => {
if (err) {
console.log("Error:", +err);
}
else {
for(var i = 0;i<result.length;i++){
res.send(result[i].Name);
}
db.close();
}
});
});
});
Please let me know what I did wrong in above code.
THANKS
It looks like you're trying to send multiple responses in a loop using Response.Send() as a response is only sent once.
This won't work, you'll need to create an array of names, and then use Response.Send() to do this once.
Using res.send(result.map(r => r.name)) would probably work
You should aggregate the results into a variable and then call res.send() only once:
let resultString;
for(var i = 0;i<result.length;i++){
resultString += result[i].Name + '\n';
}
res.send(resultString);
If you want to stream the results, you can use res.write() and when done call res.end()
You can not use res.send() multiple time in a for loop, try somthing like this
var data=[];
for(var i = 0;i<result.length;i++){
data.push(result[i].Name);
}
res.send(data);
app.post('/offers',(req, res) => {
MongoClient.connect(url, (err, db) => {
if(err) throw err;
var dbo = db.db('Tiffino_db');
dbo.collection("Offers")
.find({},{ projection: { _id: 0 } })
.toArray((err, results) => {
if (err) {
console.log("Error:", +err);
}
else {
response = results.map(result => result.Name);
//res.send(response);
// in json format
res.json(response);
db.close();
}
});
});
});
...
...
else {
output = result.map(offer => offer.name);
res.send({output});
db.close();
}
This should work as you can only send response once on a single response object and you are calling that for results.length times.
I'm pretty sure you're not supposed to be calling res.send(...) multiple times. Since you're calling it inside a loop, it will send the first document and fail in the next as expected.
Background:
I must create or update an document based on post request that I have zero control over. I'm calling the function updateOrCreate()
Question:
How can I properly find a document by an field called nuid without using _id in mongo/mongoose
example payload:
curl -H "Content-Type: application/json" -X POST -d '{"participant":{"nuid":"98ASDF988SDF89SDF89989SDF9898"}}' http://localhost:9000/api/things
thing.controller:
exports.updateOrCreate = function(req, res) {
//Thing.findByNuid() will not work but it will explain what i'm trying to accomplish
/**
Thing.findByNuid(req.body.participant.nuid, function (err, thing) {
if (err) { return handleError(res, err); }
if(!thing) {
Thing.create(req.body.participant, function(err, thing) {
if(err) { return handleError(res, err); }
});
}
var updated = _.merge(thing, req.body.participant);
updated.save(function (err) {
if (err) { return handleError(res, err); }
});
});
**/
//this block will fetch all the things that have nuids but that seems really heavy and awful practice
Thing.find({'nuid':req.body.participant.nuid}, function(err, thing){
console.log(thing);
});
// This block is here to communicate this will create a new thing as expected.
Thing.create(req.body.participant, function(err, thing) {
if(err) { return handleError(res, err); }
});
}
Schema
var ThingSchema = new Schema({
nuid: String
});
UPDATE:
var query = {"nuid": req.body.participant.nuid};
var update = {nuid: 'heyyy'};
Thing.findOneAndUpdate(
query,
update,
{upsert: true},
function(err, thing){
console.log(thing, "thing");
console.log(err, "err");
}
);
I would use findOneAndUpdate first and then based on the result do an insert. findOneAndUpdate use mongoDB findAndModify command.
You should also look at new & upsert options of it which would create a document if not found.
I can connect to my database from node.js using the MongoClient. I amb able to write, update and remove docs from a collection. But I am not able to retrieve data from it. This is my code:
var mongoClient=require('mongodb').MongoClient;
var mongoDbObj;
mongoClient.connect('mongodb://127.0.0.1:27017/trendoa', function(err, db){
if(err){
console.log(err);
}else{
global.db = db;
};
var col = global.db.collection('twitter_accounts_mon');
// create
var doc1 = {'hola':'sushi'};
col.insert(doc1, function(err, result) {
callback(err);
});
// update
col.update({hola:'jordi'}, {$set:{hola:'joan'}}, {w:1}, function(err, result) {});
// delete
col.remove({hola:'jordi'}, function(err, result) {
callback(err);
});
// read
col.find().toArray(function(err, docs) {
console.log(docs);
});
What I'm trying to do in the last lines of code is to get all the documents using find() but it doesn't return any results.
Through the mongo shell, using this command I get data on screen:
db.twitter_accounts_mon.find()
I don't know what I'm doing wrong. Thanks!
the nodejs callbacks must nest, ie only search the collection once the db is open
mongoClient.connect('mongodb://127.0.0.1:27017/trendoa', function(err, db){
var col = db.collection('twitter_accounts_mon');
coll.find({}, function(err, cursor) {
cursor.toArray(function(err, data) {
// process the data array
}
}
}
According to the MongoDB documentation on the Node.js driver, the find method does not execute the actual query, it builds an instance of a cursor that you then use to retrieve data. thus, you need to handle the result of the query.
var entireCollectionArray = col.find().toArray(function(err, items) {});
entireCollectionArray.forEach(function (element) {
console.log(element);
});