Demystifying CQRS, Event Sourcing and Domain-Driven Design — Part 1

In the API Economy world, Microservice has brought a huge breakthrough to design complex business models into small domain level business models which are maintainable, robust and supports quick deployment methodology.

So moving one step ahead and diving deep into the microservice architecture, each service in microservice serve the purpose of driving business APIs. In the continued development of the service is getting expanded and at some point in time, while scaling the service, it becomes unmaintainable.

What is CQRS and how it helps to design microservices?

CQRS stands for Command Query Responsibility Segregation which allows you to separate the current actions of the application with commands and queries and make them loosely coupled. It would look like we are deciding a different route for accessing the application data and manipulating the application data.

We can design read APIs when we need to access application data as single responsibility and write APIs when we need to update the application data. With CQRS we can separate these and make the states of the application more maintainable.

CQRS, Event Sourcing and Domain-Driven Design Architecture is shown below. We will discuss this architecture in the next part.

What is Event Sourcing?

In an application, the transaction is a significant part of service designing and it has to be reliable and atomic. In addition, a transaction made by a user impacts another part of the application, and the application has to act upon it which needs to be taken care of while making the transaction.

Event sourcing helps to decouple the transaction and its impact on the application using an event-based approach. The event-based approach works on an observer pattern where one party can subscribe to events of another party.

The event producer will create an event and publish that event into the Event Bus. on the other side subscriber of the event will subscribe to the published event from the Event Bus.

Domain-Driven Design

DDD is an approach to design the Domain Layer(Business Layer) of the application, it eases the creation of complex business models into a connected piece of domain models. It comes with its own principle as given below.

• While design the domain model, focus on the core part of the domain and domain logic only.
• Build the complex business model on connected domain models. In addition it should be able to add/remove domain model without impacting other domain models.
• In order to improve the complex business model, keep in touch with domain experts and solves any domain-related queries.

So I have covered the initial part of the CQRS, Event Sourcing and Domain-Driven Design. In the next part, we will be diving deep into the architecture of Domain-Driven Design.

One last word

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