ASP.NET service template

dotnet new trellis-asp · NuGet package Trellis.AspTemplate

A single, well-structured ASP.NET Core service built on the Trellis framework, using Domain-Driven Design and Railway-Oriented Programming. Reach for this when you're building one focused service rather than a fleet of them.

Solution structure

The template follows a strict, inward-pointing dependency flow:

MyService/
├── Domain/        # Aggregates, entities, value objects, domain events, specifications
├── Application/   # Commands, queries, handlers, repository interfaces
├── Acl/           # DbContext, EF Core configuration, repository implementations (the Anti-Corruption Layer)
├── Api/           # Controllers, DTOs, Program.cs, the composition root
└── *.slnx         # Solution file

Layer	May depend on	Never depends on
Domain	Trellis primitives only	EF Core, ASP.NET, Mediator
Application	Domain, Mediator	ASP.NET, EF providers
Acl	Application, EF Core	Api
Api	Application, Acl	Domain persistence details

Why "Acl"? It's the Anti-Corruption Layer — it adapts external systems (SQL Server, queues, other services) to your domain model, instead of the vaguer "Infrastructure".

What's wired up

Out of the box the service has every cross-cutting capability: date-based API versioning, Service Level Indicators, idempotent writes, RFC 9457 ProblemDetails, an OpenAPI document with a Scalar UI, OpenTelemetry, actor-based authorization, the mediator pipeline, and health checks. EF Core is configured with Trellis conventions and interceptors.

API versioning by namespace

Controllers live in date-stamped folders and namespaces — one folder per version:

Api/src/2026-03-26/Controllers/TodosController.cs   →  namespace MyService.Api.v2026_03_26.Controllers
Api/src/2026-12-01/Controllers/TodosController.cs   →  namespace MyService.Api.v2026_12_01.Controllers

The version is derived from the namespace — no [ApiVersion] attributes to maintain. To add a version, copy the latest folder, rename the namespace, and evolve it independently. Older versions stay frozen.

The reference implementation

A small Todo domain ships as a worked example of every pattern: scalar and composite value objects, a RequiredEnum smart enum, an aggregate with a lazy state machine, always-valid commands with TryCreate, resource-based authorization, repositories returning Maybe<T>, ETag concurrency, and version-mapped controllers. Read it before replacing it — it's the fastest way to learn the conventions.

Build and test

dotnet build MyService.slnx -c Release        # Release enforces code-style as errors
dotnet test  --solution MyService.slnx -c Release --filter-not-trait "Category=Integration"