This question already has an answer here:
NodeJS Can't Access Variable Inside Callback
(1 answer)
Closed 7 years ago.
I have the following code:
var db;
MongoClient.connect("mongodb://localhost:27017/mobregserver", function(err, database) {
if(!err) {
console.log("We are connected");
}
db = database;
});
db.collection('bbr').insert({fields: "fields", files: "files"}, {upsert:true}, function(err, result) {
if(!err){
console.log("written");
}
});
And I get the following output:
We are connected
TypeError: Cannot call method 'collection' of undefined
var db;
MongoClient.connect("mongodb://localhost:27017/mobregserver", function(err, database) {
if(!err) {
console.log("We are connected");
db = database;
db.collection('bbr').insert({fields: "fields", files: "files"}, {upsert:true}, function(err, result) {
if(!err){
console.log("written");
}
});
}
});
Connect method is asyncrone, so your db variable will be initialized much later, then you start using it. Try this code:
MongoClient.connect("mongodb://localhost:27017/mobregserver", function(err, database) {
if(err) {
// Here, it may be better to interrupt further work in case of error
console.log('fail', err);
return;
}
var db = database;
db.collection('bbr').insert({fields: "fields", files: "files"}, {upsert:true}, function(err, result) {
if(!err){
console.log("written");
}
});
});
EDIT
A full example of nodejs server, taken from here
var express = require('express');
var mongodb = require('mongodb');
var app = express();
var MongoClient = require('mongodb').MongoClient;
var db;
// Initialize connection once
MongoClient.connect("mongodb://localhost:27017/integration_test", function(err, database) {
if(err) throw err;
db = database;
// Start the application after the database connection is ready
app.listen(3000);
console.log("Listening on port 3000");
});
// Reuse database object in request handlers
app.get("/", function(req, res) {
db.collection("replicaset_mongo_client_collection").find({}, function(err, docs) {
docs.each(function(err, doc) {
if(doc) {
console.log(doc);
}
else {
res.end();
}
});
});
});
Related
I am using MongoDB to insert a record into the database, every time the post method is called. I know I do not want to connect to the db inside of the post function every time, but this is giving me errors? How can I correct this?
var mongo = require('mongodb');
var url = 'mongodb://localhost:27017/Wedding'
var db = function() {
mongo.connect(url, function(err, db){
if (!err){
return db;
}
});
}
app.post('/rsvp', function (req, res) {
var item ={
name: req.body.name,
attending: req.body.attending,
};
insertItem(item);
res.sendFile(path.join(__dirname + '/confirm.html'));
})
function insertItem(item){
db.collection('rsvpList').insertOne(item, function(err, result){
assert.equal(null, err);
})
}
I am getting this error:
TypeError: Object function () {
mongo.connect(url, function(err, db){
if (!err){
return db;
}
});
} has no method 'collection'
at insertItem (C:\Users\A587092\Documents\weddingWebsite\server.js:53:8)
at app.listen.host (C:\Users\A587092\Documents\weddingWebsite\server.js:38:4)
at Layer.handle [as handle_request] (C:\Users\A587092\Documents\weddingWebsite\node_modules\express\lib\router\layer.js:95:5)
The problem is your db does not point to the Mongo instance rather to a function!
Try this -
var mongo = require('mongodb');
var url = 'mongodb://localhost:27017/Wedding'
var db;
mongo.connect(url, function(err, connectedDB){
if (!err){
db = connectedDB;
}
});
You couldn't simply return a value from an asynchronous method:
You should use a callback function:
var connectDb = function(url, cb) {
mongo.connect(url, function(err, db){
if ( err ) {
cb( err );
}
cb(null, db);
});
};
Usage:
function insertItem(item) {
connectDb(url, function(error, db) {
if ( error ) {
throw error;
}
db.collection('rsvpList').insertOne(item, function(err, result) {
assert.equal(null, err);
});
});
}
Or a promise:
var connectDb = function(url) {
return new Promise(function(resolve, reject) {
mongo.connect(url, function(err, db){
if ( err ) {
reject(err);
}
resolve(db);
});
});
};
Usage:
function insertItem(item) {
connectDb(url)
.then(function(db) {
db.collection('rsvpList').insertOne(item, function(err, result) {
assert.equal(null, err);
});
}, function(err) {
throw err;
});
}
I change the function name from db to connectDb because we want to connect to db and then doing something after connecting. and this way your code reads well.
Also note that here also your insertItem function doing an asynchronous task so if you need the result outside of this function you should implement a similar approach, i leave it to you ;)
Here is my code
// Retrieve
var MongoClient = require('mongodb').MongoClient;
// Connect to the db
MongoClient.connect("mongodb://localhost:27017/exampleDb", function(err, db) {
if(!err) {
console.log('we are connected');
}
var k ='testt';
var collection = db.collection(k);
var doc1 = {'hello':'doc1'};
var doc2 = {'hello':'doc2'};
var lotsOfDocs = [{'hello':'doc3'}, {'hello':'doc4'}];
collection.insert(doc1);
collection.insert(doc2, {w:1}, function(err, result) {});
collection.insert(lotsOfDocs, {w:1}, function(err, result) {});
});
and it is is showing this error "Cannot read property 'collection' of null".
The issue is you are directly calling db.collection irrespective of whether db connection is successful or not. You need to check whether there is an error in db connection. db.collection works only when the DB connection is successful. Check below example for better understanding
MongoClient.connect('mongodb://localhost:27017/test',function(err,db){
if(err)
{
console.log(err);
}
else
{
console.log("Connected to db");
db.collection('testt').insert({"doc1":"hello"},function(err,data){
if(err)
{
throw(err);
}
else
{
console.log("sucessfuly inserted");
}
})
How to manage mongodb connections in a nodejs webapp?
The answer of that question is superb. I would like code however to show this. I've tried the following but since it connects async the connection is not ready by the time I want to do my database query. I'm wondering how do others do this?
'use strict';
// database stuff
var mongodb = require('mongodb'); // mongodb drivers
var MongoClient = mongodb.MongoClient; // interface
var url = 'mongodb://127.0.0.1:27017/self';
// generator flow control
var co = require('co');
// database connect function
var dbConnect = function (url) {
// get the db object
MongoClient.connect(url, {
safe: true
}, function (err, db) {
if (err) throw err;
console.log('mongodb connection successful');
return db;
});
};
var db = dbConnect(url);
// generator function with flow control
co(function* () {
console.log('starting db query');
// count documents in collection
var result =
yield new Promise(function (resolve, reject) {
if (err) reject(err);
db.collection('test').count(function (err, res) {
if (err) reject(err);
resolve(res);
});
});
// output number of documents in collection
console.log(result);
});
// more code....
I would like to use the variable db anywhere in my app.
Here maybe one way to reuse the connection.
var myDb;
//reuse connection if already created
function connect(callback) {
if (myDb === undefined) {
MongoClient.connect('mongodb://127.0.0.1:27017/test', function(err, db) {
if(err) { return callback(err)};
myDb = db;
callback(null, db);
});
} else {
callback(null, myDb);
}
function doDBOperation(err, db) {
// your mongodb operation through db is here
co(function* () { ...
}
connect(doDBOperation);
You can wrap your database connection into promise and wait it in generator
function connect() {
return new Promise((resolve, reject) => {
MongoClient.connect(url, {safe: true}, (err, db) => {
if (err) return reject(err);
resolve(db);
});
});
}
var dbConnection = connect();
co(function* () {
var db = yield dbConnection;
// your code
});
I am trying to connect to MongoDB with user/password , this is what I did so far:
var MongoClient = require('mongodb').MongoClient;
// Connect to the db
MongoClient.connect("mongodb://${host}:27017/${db}", function(err, db) {
if(!err) {
console.log("successfully connected to the database");
}else{
console.log("Error on connecting... aborting and exiting");
return console.dir(err);
throw err;
}
db.authenticate('username', 'password', function(err, res) {
console.log("reached here");
});
});
Now I am trying to login inside the data base in order to be able to get inside Mongo Database's collections, how can I do that?
Thanks!
You can perform CURD operations like following:
var MongoClient = require('mongodb').MongoClient;
// Connect to the db
MongoClient.connect("mongodb://${host}:27017/${db}", function(err, db) {
if(!err) {
console.log("successfully connected to the database");
//here you can perform operation
var collection = db.collection('test');
var doc1 = {'hello':'doc1'};
var doc2 = {'hello':'doc2'};
collection.insert(doc1);
}else{
console.log("Error on connecting... aborting and exiting");
return console.dir(err);
throw err;
}
db.authenticate('username', 'password', function(err, res) {
console.log("reached here");
});
});
If I run this using node it prints "Connected to Database":
var MongoClient = require("mongodb").MongoClient;
MongoClient.connect("mongodb://localhost/db1", function(err, db) {
if (err) {
throw err;
}
console.log("Connected to Database");
db.close();
});
However if I try to run it with a Grunt task it does nothing and silently.
module.exports = function(grunt) {
return grunt.registerTask("task", "subtask", function() {
var MongoClient = require("mongodb").MongoClient;
return MongoClient.connect("mongodb://localhost/db1", function(err, db) {
if (err) {
throw err;
}
console.log("Connected to Database");
db.close();
});
});
};
Can anyone tell me why this should be and perhaps provide a workaround?
Everything works as it should be.
Database connections are async and therefore grunt "kills off" you task before the connection is ever established.
You task should look like this:
module.exports = function(grunt) {
return grunt.registerTask("task", "subtask", function() {
var done = this.async();
var MongoClient = require("mongodb").MongoClient;
MongoClient.connect("mongodb://localhost/db1", function(err, db) {
if (err) {
done(false);
}
console.log("Connected to Database");
db.close();
done();
});
});
};
There is an entire section in the grunt documentation about this: Why doesn't my asynchronous task complete?