Domain layer intro

Domain Layer

05:25

Summary

This lesson introduces the Domain layer as the foundational starting point when implementing Clean Architecture in a Flutter application. Using an analogy of constructing a building, the instructor explains that just as engineers must draw blueprints before workers lay bricks, developers must define the application's core rules and behaviors before writing UI or data fetching code. The Domain layer dictates what the application will do without concerning itself with how those actions are implemented. Consequently, attempting to build UI or State Management first is counterproductive, as those components rely on the predefined business rules established within the Domain layer.

Key Ideas

The Domain layer is the mandatory starting point when implementing Clean Architecture.
It functions as the architectural blueprint or contract for the application, defining exactly what the app will do.
Implementation details (how the app works) are deferred to other layers (like Data or Presentation) after the Domain layer is established.
The Domain layer is completely independent of the UI and State Management.
State Management (e.g., BLoC, Provider) cannot be implemented first because it requires knowing the UseCases and Entities defined in the Domain layer.

Code Snippets

Empty — fill this in later. Open the manifest and add content here.

Architecture Insight

Architecture insight

The Domain layer is the only layer that owes nothing to the others. Entities, repository contracts, and use cases are pure Dart — no Flutter widgets, no http client, no hive boxes. If a file in domain/ imports anything from data/ or presentation/, the dependency rule has already been broken.

That purity is what lets you swap the API tomorrow, the UI next year, and still keep the same use cases running. The instructor's "blueprint vs. builder" analogy is the same idea: the blueprint doesn't change because you swap concrete for brick.

Looking ahead — Every layer that follows points back at this one. The data layer implements its repository contracts; the presentation layer calls its use cases.

My Notes

Analogy: The building construction analogy is a great mental model for why we don't start with the UI or Data layers. You don't lay bricks (Data/UI) without a blueprint (Domain).
Independence: A crucial point for building professional documentation is that the Domain layer is framework-agnostic. It only cares about pure Dart code, Entities, and UseCases, completely ignoring if we eventually use Bloc or Riverpod.
Gotcha avoidance: Many beginners try to build the UI first. A structured study approach shows that defining the business rules and data flow first prevents messy refactoring later when UI-driven models fail to match backend reality.
[Editor's note] Compiling this sequential analysis highlights that in a real-world workflow, UI mockups often inform the design of the Domain layer's UseCases, even if the pure Dart code for the Domain layer is written first.