Evolution of C# Software Architecture: From 3-Layer Monoliths to Vertical Slicing

Building software in C#: part 1 - history

Miroslav Thompson examines the historical trajectory of C# development starting in 2010. The evolution spans from basic layered architectures to complex DDD and Event Sourcing paradigms.

Why This Matters

There is a persistent gap between theoretical architectural ideals and practical implementation. While models like Onion Architecture or DDD/ES/CQRS promise purity, they often introduce extreme complexity—such as difficulties in enforcing simple uniqueness constraints—resulting in developers spending more time on ‘engineering a starship’ than shipping production features.

Key Insights

• The dominant trend in 2010 was the 3-layer monolithic architecture, consisting of presentation, business, and database layers.
• Domain-Driven Design (DDD) prioritizes the ‘domain’ as the core business logic, requiring a ‘domain expert’ to maintain a ubiquitous language.
• The combination of DDD, Event Sourcing (ES), and CQRS creates high overhead due to requirements for snapshots, versioning, and handling eventual consistency.
• MediatR shifted development toward treating the domain as a flat list of distinct units of work via request pipelines.
• Vertical Slicing replaces technical layer organization with feature-based grouping, placing UI, business logic, and data access for a specific feature into a single folder.

Practical Applications

• )Use case: Single-server web applications using Vertical Slicing to group all relevant layers within feature folders for better modularity.
• )Pitfall: Misinterpreting 3-layer architecture as independent components that communicate arbitrarily, leading to UI layers communicating directly with databases.

References:

• https://dev.to/czmirek/building-software-in-c-part-1-history-1p1i