Mongoose Connection

问题:

I read the quick start from the Mongoose website and I almost copy the code, but I cannot connect the MongoDB using Node.js.

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/test');

exports.test = function(req, res) {
  var db = mongoose.connection;
  db.on('error', console.error.bind(console, 'connection error:'));
  console.log("h1");
  db.once('open', function callback () {
    console.log("h");
  });
  res.render('test');
};

This is my code. The console only prints h1, not h. Where am I wrong?

回答1:

When you call mongoose.connect, it will set up a connection with the database.

However, you attach the event listener for open at a much later point in time (when a request is being handled), meaning that the connection is probably already active and the open event has already been called (you just weren't yet listening for it).

You should rearrange your code so that the event handler is as close (in time) to the connect call as possible:

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/test');
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function callback () {
  console.log("h");
});

exports.test = function(req,res) {
  res.render('test');
};

回答2:

The safest way to do this, it to "listen for the connect event". This way you don't care how long it takes for the DB to give you a connection.

Once that is done - you should start the server. Also.. config.MONGOOSE is exposed across your app, so you only have one DB connection.

If you want to use mongoose's connection, simply require config in your module, and call config.Mongoose. Hope this helps out someone!

Here's the code.

var mongoURI;

mongoose.connection.on("open", function(ref) {
  console.log("Connected to mongo server.");
  return start_up();
});

mongoose.connection.on("error", function(err) {
  console.log("Could not connect to mongo server!");
  return console.log(err);
});

mongoURI = "mongodb://localhost/dbanme";

config.MONGOOSE = mongoose.connect(mongoURI);

回答3:

I had the same error popping up. Then I found out that I didn't have a mongod running and listening for connections. To do that you just need to open another command prompt (cmd) and run mongod

回答4:

Mongoose's default connection logic is deprecated as of 4.11.0. It is recommended to use the new connection logic:

• useMongoClient option
• native promise library

---

Here is the example from npm module: mongoose-connect-db

// Connection options
const defaultOptions = {
  // Use native promises (in driver)
  promiseLibrary: global.Promise,
  useMongoClient: true,
  // Write concern (Journal Acknowledged)
  w: 1,
  j: true
};

function connect (mongoose, dbURI, options = {}) {
  // Merge options with defaults
  const driverOptions = Object.assign(defaultOptions, options);

  // Use Promise from options (mongoose)
  mongoose.Promise = driverOptions.promiseLibrary;

  // Connect
  mongoose.connect(dbURI, driverOptions);

  // If the Node process ends, close the Mongoose connection
  process.on('SIGINT', () => {
    mongoose.connection.close(() => {
      process.exit(0);
    });
  });

  return mongoose.connection;
}