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What is domain layer?

Posted on:July 5, 2022 at 02:05 AM

The Importance of the Domain Layer in Your Application

In the realm of software development, the Domain Layer stands out as the most crucial element, embodying processes, calculations, and business rules. This layer encapsulates the logic that propels a business to generate revenue, granting it a unique identity and a competitive edge.

The Heart of the Application

Visualize the “Domain Layer” as the heart of your application, with other layers dependent on it. Arrows pointing towards these layers signify their reliance, while the absence of arrows highlights the independence of the Domain Layer. This layer is the bedrock upon which the entire application stands.

Business Change Resistance

As the core of the system, the Domain Layer should be designed to withstand changes. This resilience extends beyond code modifications; it is about adapting to shifts in business dynamics.

Consider scenarios in the financial industry where business rules align with legal requirements. Sudden changes in legislation necessitate corresponding adjustments in your rules; failure to do so renders the system obsolete. Similarly, in an evolving business landscape, feedback from customers might trigger alterations in business rules.

The vitality of the system resides with the business. As it grows, so does the domain, making it imperative to craft a domain layer that accommodates these inevitable changes.

Good Practices for a Robust Domain Layer

1. No Dependencies, No Frameworks

The code in the domain layer should remain pristine—a pure model of business objects. Avoid introducing dependencies on frameworks or references to other projects. Infrastructure leaks into the domain compromise maintainability.

2. Ubiquitous Language

Adopt the language used by the business during client meetings. Test names and class names should be comprehensible to a business expert, fostering clear communication between developers and stakeholders.

3. Rich Model Design Over Anemic Model Design

Design entities with both properties and behaviors. Move beyond “Anemic entities” that merely reflect database structures. Enriched entities consolidate business logic in a single, easily modifiable location.

4. High Hermetization

Guard against exposing excessive methods or properties to the public. Overexposure allows other programmers to use domain logic in unintended ways, leading to leaks and duplication of business rules.

5. Persistence Ignorance

The domain layer should be oblivious to its persistence state. Postponing awareness of data or relational status facilitates unit testing and enhances the layer’s adaptability.

Real Example: “Estimation Tool”

Consider the “Estimation Tool,” a project managing pricing services in IT companies. Examining the domain layer structure reveals a focus on pure business logic. The Valuations module, consisting of Valuation, Proposals, Clients, and Employee ID, showcases events for proposals—approval or rejection.

Omitted are technical details like DbContext or Handlers, emphasizing a pure representation of business entities. This intentional separation underscores the clarity and effectiveness of the Domain Layer.