No matter what I try callback of MongoClient.connect() is never called. Have tried several alternatives but nothing seems to make the callback function invoked. I am using node.js mongodb driver 2.1.6 and Express routes. Below is the directory structure:
/
node_modules/
exampleServers/
routes/
mongo.js
notes.js
Below is the code for mongo.js which am trying to invoke from notes.js for getting DB connections
var MongoClient = require('mongodb').MongoClient
var state = {
db: null,
}
exports.connect = function(url, done) {
if (state.db) return done()
console.log("***REACHES UPTO HERE");
MongoClient.connect(url, function(err, db) {
console.log("***NEVER REACHES HERE");
if (err) return done(err)
state.db = db
done()
})
}
exports.get = function() {
console.log("state.db" + state.db);
return state.db
}
exports.close = function(done) {
if (state.db) {
state.db.close(function(err, result) {
state.db = null
state.mode = null
done(err)
})
}
}
Related
I have written the following code in Nodejs which is saving data in MongoDB:
function insertDoc(db,data){
return new Promise(resolve => {
callback=db.collection('AnalysisCollection').insertOne(data).then(function(response,obj){
console.log("Inserted record");
resolve(obj);
//console.log(obj);
// response.on('end',function(){
// resolve(obj);
// });
//return resolve(obj);
}).then(() => { return obj }
).catch(function(error){
throw new Error(error);
});
})
}
I am calling the above function from the main function like this:
async function cosmosDBConnect(nluResultJSON){
try{
//console.log("Inserting to cosmos DB");
console.log(nluResultJSON);
var url = config.cosmos_endpoint;
var result="";
var data = JSON.parse(JSON.stringify(nluResultJSON));
MongoClient.connect(url, function(err, client) {
assert.equal(null, err);
var db = client.db('NLUAnalysisDB');
// insertDoc(db, data, function() {
result=insertDoc(db, data, function() {
console.log(result);
client.close();
//return data._id;
});
});
}
catch (e) {
console.log(e);
}
}
module.exports = { cosmosDBConnect };
But in cosmosDBConnect, I am getting 'undefined' for the result, though in insertDoc I am getting the output for'obj' with _id for the inserted record.
Please help me to return this _id to cosmosDBConnect.
You are use callbacks inside of async function, which creates internal scopes. So your return aplies to them instead of whole function. You should use Promise-based methods inside of async function using await (without callbacks) or wrap whole function into own Promise otherwise.
Example:
function cosmosDBConnect(nluResultJSON) {
return new Promise((resolve, reject) => {
var url = config.cosmos_endpoint;
var result = '';
var data = JSON.parse(JSON.stringify(nluResultJSON));
MongoClient.connect(url, function(err, client) {
if (err) return reject(err);
assert.equal(null, err);
var db = client.db('NLUAnalysisDB');
insertDoc(db, data).then(obj => {
console.log(obj);
client.close();
return resolve(data._id);
});
});
});
}
Also you need to understand that your insertDoc return Promise and do not accept callback you tried to pass.
Ref: async function
result = insertDoc(db, data).then((data) => {
console.log(data);
}).catch(err => console.error(err));
I am separating the connect function of MongoDB to a separate module, so that the mongoDB connection is reusable. The issue is, I could not get the client/DB variable outside the connect function. It shows undefined.
var MongoClient = require('mongodb').MongoClient;
var _client;
var mongoURL = "mongodb://localhost:27017/";
module.exports = {
connectToMongoServer: (callback) => {
MongoClient.connect(mongoURL,{ useNewUrlParser: true },function(err,client){
_client = client;
return callback(err);
});
},
getClient: () => {
return _client;
}
};
Within the connect function, the _client details contains the information, but if I return it using getClient, it shows undefined.
MongoDB - v3.6.5
Node - v9.9.0
I've made up a snippet which should work the same ad your code, and it works.
So I think the problem is how you are calling your function getClient(); are you sure you are calling it after it get connected?
var _client;
function someAsyncFunc(callback) {
setTimeout(() => callback(false, 'client'), 500);
}
const file = {
connectToMongoServer: (callback) => {
someAsyncFunc(function(err, client) {
_client = client;
return callback(err);
});
},
getClient: () => {
return _client;
}
};
console.log('display one :', file.getClient());
file.connectToMongoServer((err) => {
console.log('display error :', err);
console.log('display two :', file.getClient());
});
I am using node js express and calling model from the controller.When I call model form controller and getting a result in result variable and print it in console.log(result) it's undefined.
Controller
var user_model=require('../models/user');
exports.get_user = function(req, res) {
var result = user_model.get_users();
console.log(result);
}
Model
var connection=require('../config/connection');
exports.get_users = function() {
connection.query('SELECT * FROM users', function(err, rows) {
if(err) {
retrun err;
}
return rows;
});
}
This is happening because you are consoling the result before the query has finished. Node is asynchronous. Unlike php node doesn't wait for the query to finish before going to the next line.
Use promise to handle async calls
// **Controller**
var user_model = require('../models/user');
exports.get_user = function (req, res) {
user_model.get_users().then((result) => {
console.log(result);
}).catch(err => console.log(err));
}
// **Model**
var connection = require('../config/connection');
exports.get_users = function () {
return new Promise((resolve, reject) => {
connection.query('SELECT * FROM users', function (err, rows) {
if (err) {
reject(err);
}
resolve(rows);
});
}
})
}
I am creating a 'refresh data' function in Node and I cannot figure out where to place the callbacks and returns. The function continues to run. Below is a list of things the function should do. Could someone help out?
Check if a user has an api id in the local MongoDB
Call REST api with POST to receive token
Store token results in a MongoDB
Terminate function
./routes/index.js
router.post('/refresh', function(req, res) {
var refresh = require('../api/refresh');
refresh(req, function() { return console.log('Done'); });
});
../api/refresh.js
var callToken = require('./calltoken');
var User = require('../models/user'); // Mongoose Schema
module.exports = function(req, callback) {
User.findOne( {'username':req.body.username}, function(err, user) {
if(err) { console.log(err) }
if (user.api_id == 0) {
callToken.postToken(req.body.username, callback);
} else { // Do something else }
});
};
./calltoken.js
var request = require('request');
var Token = require('../models/token'); // Mongoose Schema
module.exports = {
postToken: function(user, callback) {
var send = {method:'POST', url:'address', formData:{name:user} };
request(send, function(err, res, body) {
if(err) { console.log(err) }
if (res.statusCode == 201) {
var newToken = new Token();
newToken.token = JSON.parse(body).access_token['token'];
newToken.save(function(err) {
if(err) { console.log(err) }
return callback();
});
}
});
}
};
I'm not an expert in Express but everywhere in you code in lines with if(err) { console.log(err) } you should stop execution (maybe of course not - up to you app) and return 400 or 500 to client. So it can be something like
if(err) {
console.log(err);
return callback(err); // NOTICE return here
}
On successful execution you should call return callback(null, result). Notice null as a first argument - it is according nodejs convention (error always goes as first argument).
I am trying to connect to mongodb from node and I am getting below error
node_modules\mongodb\lib\mongo_client.js:458
throw err
^
ReferenceError: connect is not defined
I am using the mongodb module version
2.0.48
I am trying to run a simple test code
(function (dbase) {
var mdb = require('mongodb');
var mongoUrl = "mongodb://localhost:27017/theBoard";
var connection;
dbase.dbConnection = function (next) {
if (connection) {
next(null, connection);
} else {
mdb.MongoClient.connect(mongoUrl, function(err, db) {
if (err) {
next(err, null);
} else {
console.log("connected");
connection = { db: db , notes: db.collection("notes")};
next(null, connection);
}
});
}
}
Can someone please help me understand this issue.
---Additional information
data module -
(function (data) {
var mdb = require('./db.js');
data.GetCategory = function() {
mdb.dbConnection(function(err, db) {
if (err)
console.log("Error connecting to mango");
if (connect) {
db.notes.count(function(err, count) {
if (err)
console.log("Failed to retreive collection");
else
console.log("Count - "+count);
});
console.log("Connected");
}
});
}})(module.exports);
db.js
(function (dbase) {
var mdb = require('mongodb');
var mongoUrl = "mongodb://localhost:27017/theBoard";
var connection;
dbase.dbConnection = function (next) {
if (connection) {
next(null, connection);
} else {
mdb.MongoClient.connect(mongoUrl, function(err, db) {
if (err) {
next(err, null);
} else {
console.log("connected");
connection = { db: db , notes: db.collection("notes") };
next(null, connection);
}
});
}
} })(module.exports);
Controller -
(function (controller) {
var data = require('.././data');
controller.init = function (app) {
app.get("/", handleRequest);
}
var handleRequest = function (req, res) {
data.GetCategory();
var a = {};
a.send = "Mamma is coming home";
res.send(a);
}
})(module.exports);
Just in case some one runs into an issue like this due to bad coding practice even if it for test purpose is to never have function names which are the same as the function names in the API. In db.js I had an undefined variable named connect which trowing and error when it was accessed and since it was called through the API function called "connect" the error was thrown by the API leading me to believe that the API function had an issue