Mongoose saving

So, the output of mongoose.model() is a model, and a given model is always tied to one connection.

By default, most folks just use the connection and connection pooling available from mongoose.connect(). Once you call that, the cached mongoose module is using a singleton connection object under the hood. So for example, if I'm calling your model, I'd do this:

const mongoose = require('mongoose');const User = require('./models/user');mongoose.connect(); // or pass in a custom URL// from here, User will default to the mongoose-internal connection created in the previous line

If I want to use multiple connections, I cannot use the mongoose internal singleton, so I would have to do the operations with the created connection. For example:

// ./schemas/user.js// You now export the Schema rather than the module in your file//module.exports = mongoose.model('User', User);module.exports = User;

Then in the calling code:

const config = require('./config'); // presumably this has a couple mongo URLsconst mongoose = require('mongoose');const UserSchema = require('./schemas/user');const conn1 = mongoose.createConnection(config.url1);const conn2 = mongoose.createConnection(config.url2);const User1 = conn1.model('User', UserSchema);const User2 = conn2.model('User', UserSchema);// now any users created with User1 will save to the first db, users created with User2 will save to the second.