Dotnet Project Structure

.NET Project Structure and Build Configuration

When to Use This Skill

Use this skill when:

• Setting up a new .NET solution with modern best practices
• Configuring centralized build properties across multiple projects
• Implementing central package version management
• Setting up SourceLink for debugging and NuGet packages
• Automating version management with release notes
• Pinning SDK versions for consistent builds

Related Skills

• `dotnet-local-tools` - Managing local .NET tools with dotnet-tools.json
• `microsoft-extensions-configuration` - Configuration validation patterns

Solution File Format (.slnx)

The .slnx format is the modern XML-based solution file format introduced in .NET 9. It replaces the traditional .sln format.

Benefits Over Traditional .sln

Version Requirements

Note: Starting with .NET 10, dotnet new sln creates .slnx files by default. In .NET 9, you must explicitly migrate or specify the format.

Example .slnx File

<Solution>
  <Folder Name="/build/">
    <File Path="Directory.Build.props" />
    <File Path="Directory.Packages.props" />
    <File Path="global.json" />
    <File Path="NuGet.Config" />
    <File Path="README.md" />
  </Folder>
  <Folder Name="/src/">
    <Project Path="src/MyApp/MyApp.csproj" />
    <Project Path="src/MyApp.Core/MyApp.Core.csproj" />
  </Folder>
  <Folder Name="/tests/">
    <Project Path="tests/MyApp.Tests/MyApp.Tests.csproj" />
  </Folder>
</Solution>

Migrating from .sln to .slnx

Use the dotnet sln migrate command to convert existing solutions:

# Migrate a specific solution file
dotnet sln MySolution.sln migrate

# Or if only one .sln exists in the directory, just run:
dotnet sln migrate

Important: Do not keep both .sln and .slnx files in the same repository. This causes issues with automatic solution detection and can lead to sync problems. After migration, delete the old .sln file.

You can also migrate in Visual Studio:

1. Open the solution
2. Select the Solution in Solution Explorer
3. Go to File > Save Solution As...
4. Change "Save as type" to *Xml Solution File (.slnx)**

Creating a New .slnx Solution

# .NET 10+: Creates .slnx by default
dotnet new sln --name MySolution

# .NET 9: Specify the format explicitly
dotnet new sln --name MySolution --format slnx

# Add projects (works the same for both formats)
dotnet sln add src/MyApp/MyApp.csproj

Recommendation

If you're using .NET 9.0.200 or later, migrate your solutions to .slnx. The benefits are significant:

• Dramatically fewer merge conflicts (no random GUIDs changing)
• Human-readable and editable in any text editor
• Consistent with modern .csproj format
• Better diff/review experience in pull requests

Directory.Build.props

Directory.Build.props provides centralized build configuration that applies to all projects in a directory tree. Place it at the solution root.

Complete Example

<Project>
  <!-- Metadata -->
  <PropertyGroup>
    <Authors>Your Team</Authors>
    <Company>Your Company</Company>
    <!-- Dynamic copyright year - updates automatically -->
    <Copyright>Copyright © 2020-$([System.DateTime]::Now.Year) Your Company</Copyright>
    <Product>Your Product</Product>
    <PackageProjectUrl>https://github.com/yourorg/yourrepo</PackageProjectUrl>
    <RepositoryUrl>https://github.com/yourorg/yourrepo</RepositoryUrl>
    <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
    <PackageTags>your;tags;here</PackageTags>
  </PropertyGroup>

  <!-- C# Language Settings -->
  <PropertyGroup>
    <LangVersion>latest</LangVersion>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <NoWarn>$(NoWarn);CS1591</NoWarn> <!-- Missing XML comments -->
  </PropertyGroup>

  <!-- Version Management -->
  <PropertyGroup>
    <VersionPrefix>1.0.0</VersionPrefix>
    <PackageReleaseNotes>See RELEASE_NOTES.md</PackageReleaseNotes>
  </PropertyGroup>

  <!-- Target Framework Definitions (reusable properties) -->
  <PropertyGroup>
    <NetStandardLibVersion>netstandard2.0</NetStandardLibVersion>
    <NetLibVersion>net8.0</NetLibVersion>
    <NetTestVersion>net9.0</NetTestVersion>
  </PropertyGroup>

  <!-- SourceLink Configuration -->
  <PropertyGroup>
    <PublishRepositoryUrl>true</PublishRepositoryUrl>
    <EmbedUntrackedSources>true</EmbedUntrackedSources>
    <IncludeSymbols>true</IncludeSymbols>
    <SymbolPackageFormat>snupkg</SymbolPackageFormat>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.SourceLink.GitHub" PrivateAssets="All" />
  </ItemGroup>

  <!-- NuGet Package Assets -->
  <ItemGroup>
    <None Include="$(MSBuildThisFileDirectory)logo.png" Pack="true" PackagePath="\" />
    <None Include="$(MSBuildThisFileDirectory)README.md" Pack="true" PackagePath="\" />
  </ItemGroup>

  <PropertyGroup>
    <PackageIcon>logo.png</PackageIcon>
    <PackageReadmeFile>README.md</PackageReadmeFile>
  </PropertyGroup>

  <!-- Global Using Statements -->
  <ItemGroup>
    <Using Include="System.Collections.Immutable" />
  </ItemGroup>
</Project>

Key Patterns

Dynamic Copyright Year

<Copyright>Copyright © 2020-$([System.DateTime]::Now.Year) Your Company</Copyright>

Uses MSBuild property functions to insert current year at build time. No manual updates needed.

Reusable Target Framework Properties

Define target frameworks once, reference everywhere:

<!-- In Directory.Build.props -->
<PropertyGroup>
  <NetLibVersion>net8.0</NetLibVersion>
  <NetTestVersion>net9.0</NetTestVersion>
</PropertyGroup>

<!-- In MyApp.csproj -->
<PropertyGroup>
  <TargetFramework>$(NetLibVersion)</TargetFramework>
</PropertyGroup>

<!-- In MyApp.Tests.csproj -->
<PropertyGroup>
  <TargetFramework>$(NetTestVersion)</TargetFramework>
</PropertyGroup>

SourceLink for NuGet Packages

SourceLink enables step-through debugging of NuGet packages:

<PropertyGroup>
  <PublishRepositoryUrl>true</PublishRepositoryUrl>
  <EmbedUntrackedSources>true</EmbedUntrackedSources>
  <IncludeSymbols>true</IncludeSymbols>
  <SymbolPackageFormat>snupkg</SymbolPackageFormat>
</PropertyGroup>

<ItemGroup>
  <!-- Choose the right provider for your source control -->
  <PackageReference Include="Microsoft.SourceLink.GitHub" PrivateAssets="All" />
  <!-- Or: Microsoft.SourceLink.AzureRepos.Git -->
  <!-- Or: Microsoft.SourceLink.GitLab -->
  <!-- Or: Microsoft.SourceLink.Bitbucket.Git -->
</ItemGroup>

Directory.Packages.props - Central Package Management

Central Package Management (CPM) provides a single source of truth for all NuGet package versions.

Setup

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

  <!-- Define version variables for related packages -->
  <PropertyGroup>
    <AkkaVersion>1.5.35</AkkaVersion>
    <AspireVersion>9.1.0</AspireVersion>
  </PropertyGroup>

  <!-- Application Dependencies -->
  <ItemGroup Label="App Dependencies">
    <PackageVersion Include="Akka" Version="$(AkkaVersion)" />
    <PackageVersion Include="Akka.Cluster" Version="$(AkkaVersion)" />
    <PackageVersion Include="Akka.Persistence" Version="$(AkkaVersion)" />
    <PackageVersion Include="Microsoft.Extensions.Hosting" Version="9.0.0" />
  </ItemGroup>

  <!-- Build/Tooling Dependencies -->
  <ItemGroup Label="Build Dependencies">