Project Structure

Core Principles

1. Central package management — Use Directory.Packages.props to manage NuGet package versions in one place. No version numbers in individual .csproj files.
2. Shared build properties — Use Directory.Build.props for common settings (target framework, nullable, implicit usings). Don't repeat in every project.
3. .slnx for solutions — The new XML-based solution format is cleaner and more merge-friendly than the legacy .sln format.
4. src/tests separation — Source projects in src/, test projects in tests/. Clear boundary.

Patterns

Solution Layout

MyApp/
├── MyApp.slnx                       # Solution file
├── Directory.Build.props             # Shared MSBuild properties
├── Directory.Packages.props          # Central package management
├── .editorconfig                     # Code style rules
├── .gitignore
├── global.json                       # SDK version pinning
├── src/
│   ├── MyApp.Api/                    # Web API (entry point)
│   │   ├── MyApp.Api.csproj
│   │   ├── Program.cs
│   │   └── Features/
│   ├── MyApp.Domain/                 # Domain entities, value objects (optional)
│   │   └── MyApp.Domain.csproj
│   └── MyApp.Infrastructure/         # EF Core, external services (optional)
│       └── MyApp.Infrastructure.csproj
└── tests/
    └── MyApp.Api.Tests/
        └── MyApp.Api.Tests.csproj

Directory.Build.props

<Project>
  <PropertyGroup>
    <TargetFramework>net10.0</TargetFramework>
    <LangVersion>14</LangVersion>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>
  </PropertyGroup>
</Project>

Directory.Packages.props (Central Package Management)

<Project>
  <PropertyGroup>
    <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
  </PropertyGroup>

  <ItemGroup>
    <!-- Versions below are illustrative — resolve the current stable versions
         with `dotnet add package <name>` (no --version flag); see the packages rule -->
    <!-- ASP.NET Core -->
    <PackageVersion Include="Mediator.Abstractions" Version="3.0.0" />
    <PackageVersion Include="Mediator.SourceGenerator" Version="3.0.0" />
    <PackageVersion Include="FluentValidation.DependencyInjectionExtensions" Version="12.0.0" />

    <!-- Data -->
    <PackageVersion Include="Microsoft.EntityFrameworkCore" Version="10.0.10" />
    <PackageVersion Include="Npgsql.EntityFrameworkCore.PostgreSQL" Version="10.0.10" />

    <!-- Observability -->
    <PackageVersion Include="Serilog.AspNetCore" Version="10.0.0" />
    <PackageVersion Include="OpenTelemetry.Extensions.Hosting" Version="1.17.0" />

    <!-- Testing -->
    <PackageVersion Include="xunit.v3" Version="3.2.2" />
    <PackageVersion Include="Microsoft.AspNetCore.Mvc.Testing" Version="10.0.10" />
    <PackageVersion Include="Testcontainers.PostgreSql" Version="4.13.0" />
  </ItemGroup>
</Project>

Project File (.csproj) with Central Package Management

<Project Sdk="Microsoft.NET.Sdk.Web">
  <!-- No TargetFramework here — inherited from Directory.Build.props -->

  <ItemGroup>
    <!-- No Version attribute — managed centrally -->
    <PackageReference Include="Mediator.Abstractions" />
    <PackageReference Include="Mediator.SourceGenerator" />
    <PackageReference Include="FluentValidation.DependencyInjectionExtensions" />
    <PackageReference Include="Microsoft.EntityFrameworkCore" />
    <PackageReference Include="Npgsql.EntityFrameworkCore.PostgreSQL" />
    <PackageReference Include="Serilog.AspNetCore" />
  </ItemGroup>

  <ItemGroup>
    <ProjectReference Include="..\MyApp.Domain\MyApp.Domain.csproj" />
    <ProjectReference Include="..\MyApp.Infrastructure\MyApp.Infrastructure.csproj" />
  </ItemGroup>
</Project>

global.json (SDK Pinning)

{
  "sdk": {
    "version": "10.0.100",
    "rollForward": "latestFeature"
  }
}

.slnx Solution Format

<Solution>
  <Folder Name="/src/">
    <Project Path="src/MyApp.Api/MyApp.Api.csproj" />
    <Project Path="src/MyApp.Domain/MyApp.Domain.csproj" />
    <Project Path="src/MyApp.Infrastructure/MyApp.Infrastructure.csproj" />
  </Folder>
  <Folder Name="/tests/">
    <Project Path="tests/MyApp.Api.Tests/MyApp.Api.Tests.csproj" />
  </Folder>
</Solution>

Naming Conventions

Anti-patterns

Don't Scatter Package Versions

<!-- BAD — version in every .csproj, version drift -->
<PackageReference Include="Mediator.Abstractions" Version="2.0.0" />  <!-- in Project A -->
<PackageReference Include="Mediator.Abstractions" Version="3.0.0" />  <!-- in Project B -->

<!-- GOOD — central management, one version -->
<!-- Directory.Packages.props: <PackageVersion Include="Mediator.Abstractions" Version="3.0.0" /> -->
<!-- .csproj: <PackageReference Include="Mediator.Abstractions" /> -->

Don't Repeat Build Properties

<!-- BAD — same properties in every .csproj -->
<PropertyGroup>
  <TargetFramework>net10.0</TargetFramework>
  <Nullable>enable</Nullable>
  <ImplicitUsings>enable</ImplicitUsings>
</PropertyGroup>

<!-- GOOD — once in Directory.Build.props, inherited everywhere -->

Don't Mix Source and Test Projects

# BAD — tests mixed with source
src/
  MyApp.Api/
  MyApp.Api.Tests/    # test project in src/

# GOOD — clear separation
src/
  MyApp.Api/
tests/
  MyApp.Api.Tests/

Decision Guide