Event Sourcing With NestJS Example

Overview

This sample code serves as a comprehensive example for establishing a Write Model within an event-sourced IoT platform. By leveraging the Event-sourcing data-persistence pattern and integrating the CQRS approach, this solution distinctly separates the Read-Model from the Write-Model. It also emphasizes the principles of Domain-Driven Development, making this a strong example for developers interested in modern software architecture.

The scope of this sample focuses on the essential functionality required to connect a new device to the platform. Built using Node.js, NestJS, and TypeScript, it showcases the integration with an Event Store implementation based on the robust framework from eventstore.org.

Features

• Event-sourced Architecture: Utilizes event-sourcing to maintain a history of state changes, providing a reliable and traceable system for IoT applications.
• CQRS Implementation: Separates the Read-Model from the Write-Model, which optimizes performance and simplifies queries while enhancing scalability.
• Domain-Driven Development: Applies DDD principles to ensure that the software model reflects the real-world use cases and business logic of IoT devices.
• Command Handler: Validates incoming commands from devices, ensuring that only correctly formatted requests trigger changes in the Domain Model.
• Event Creation and Storage: Generates corresponding events reflecting state changes, which are then stored in the Event Store for later retrieval and analysis.
• Messaging Bus Functionality: The Event Store not only persists events but also acts as a messaging bus, effectively communicating changes to the Read Model.
• Subscriber Mechanism: Implements a subscriber system for propagating events to a denormalized data store, enabling efficient data retrieval and displaying updated information to users.