Multiple databases and connections in Nodejs and MongoDB

There is a strategy in some projects that your program must read data from a database, do some processes on it, and write it in another database.
Let me give you an example, you are implementing a program that is supposed to be the “Logger” service. It collects logs from the logs database and obtains a report of them. This report will be saved in the reports database. You should separate databases because of the huge amount of data.

Implementation

So, let’s get started with setting up the project.

$ mkdir logger && cd logger

Setting up the NPM

$ npm init

Creating the entry point

$ touch app.js

Installing dependencies

$ npm i express mongoose nodemon

app.js

I don’t want to get into Architectural issues. So I want to talk about two things:

Models

Create a directory called Models

$ mkdir Models

Log.js and Report.js are the project models

Models/
  ├── Log.js
  ├── Report.js

We usually make a connection in models when we using mongoose
but this case is a little bit different

connections.js

At the root of the project create a module to handle the database connections there

connections.js has a makeNewConnection function that receives database URI and returns a connection object of that database.
We can use these connections objects in the related models

Log.js

Report.js

Each of these models is connected to the different database

That’s it. we can create layers and services around these models.
we can import Log model and read data from it, do the magic then use the Report model and save it in the Report database.
This approach is very clean and helps you to manage your database connections and not to generate spaghetti codes.

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