Why is there separate mongo.Server and mongo.Db in mongodb-native driver?

Question

I am just learning mongodb-native driver for nodejs.

I connect like this.

var mongo=require("mongodb")

var serv=mongo.Server("localhost", 27017)
var dbase=mongo.Db("MyDatabase", serv)

And that works. But if I try to create a new database connection using the same server I get an error.

var dbase2=mongo.Db("MyDatabase2", serv)

"Error: A Server or ReplSet instance cannot be shared across multiple Db instances"

But it works if a make a new server connection first.

var serv2=mongo.Server("localhost", 27017)
var dbase2=mongo.Db("MyDatabase2", serv2)

So my question is why there are 2 connection functions, one for Server and one for Db, when it seems like they must always be used together?

Why doesn't it go like this.

var dbase=mongo.Db("localhost", 27017, "MyDatabase")

I want to make my own function that does this, but I wonder if there is some other reason they are separate.

Thanks.

Answer 1

For what it's worth, you can do what you want to do by using Db#db(), which doesn't seem to appear in the official documentation but is listed in the source code of db.js as being a public API:

/**
* Create a new Db instance sharing the current socket connections.
*
* @param {String} dbName the name of the database we want to use.
* @return {Db} a db instance using the new database.
* @api public
*/

so you could do

var serv=mongo.Server("localhost", 27017);
var dbase=mongo.Db("MyDatabase", serv);
var dbase2=dbase.db("MyDatabase2");

Answer 2

Here is a link to the solution on the mongo docs, for reference. (seems like the same solution the other poster mentioned)

http://mongodb.github.com/node-mongodb-native/markdown-docs/database.html#sharing-the-connections-over-multiple-dbs

The point of separating the connection to the mongo server, and then the DB is for cases like when you want to connect to a ReplSet server, or other custom params. This way, you have a separate process connecting to a mongodb server.

The database connection call is separate simply because of the case you have here: you dont simply want to connect to a mongo server and a single db, but multiple dbs. This separation of connecting to db and server allows this flexibility.

Another Solution: Use node-mongoskin

Mongoskin does what you want to... it allows connecting to server and db all in one command. Not a solution for mongo-native, but worth considering as an alternative library for your future projects.

var mongo = require('mongoskin');
var db = mongo.db('localhost:27017/testDB');