Migration from Activities

Stable Telemetry SourceGenerator Reviewed 2026-09-16 purview-dev/telemetry-sourcegenerator Star on GitHub 36 activity c-sharp distributed-tracing dotnet events high-performance-logging instrumentation logging melt metrics nuget observability open-telemetry open-telemetry-csharp otel roslyn source-generator spans telemetry tracing

Migration from Activities

This guide covers converting hand-written ActivitySource/Activity code to generated telemetry interfaces. For the fastest path, use the IDE refactorings — this page documents the manual fallback.

Before

using System.Diagnostics;

public class OrderService
{
    static readonly ActivitySource _source = new("OrderService");

    public void PlaceOrder(int orderId)
    {
        using var activity = _source.StartActivity("PlaceOrder", ActivityKind.Internal);
        activity?.AddEvent(new ActivityEvent("Validated"));
    }
}

After

using System.Diagnostics;
using Purview.Telemetry;

[ActivitySource]
public interface IOrderServiceTracing
{
    [Activity]
    Activity? PlaceOrder(int orderId);

    [Event]
    void Validated(Activity? activity);
}

public class OrderService(IOrderServiceTracing tracing)
{
    public void PlaceOrder(int orderId)
    {
        using var activity = tracing.PlaceOrder(orderId);
        tracing.Validated(activity);
    }
}

services.AddOrderServiceTracing();

Common conversions

Original code	Generated method signature
`_source.StartActivity("PlaceOrder")`	`[Activity] Activity? PlaceOrder();`
`_source.StartActivity("Order", ActivityKind.Internal)`	`[Activity(ActivityKind.Internal)] Activity? Order();`
`activity.AddEvent(new ActivityEvent("Loaded"))`	`[Event] void Loaded(Activity? activity);`
`activity.SetBaggage("tenant", tenantId)`	`[Context] void SetTenant(Activity? activity, [Baggage] string tenantId);`
`activity.SetTag("tenant", tenantId)`	`[Context] void SetTenant(Activity? activity, [Tag] string tenantId);`

Return types

Activity-starting methods should return Activity? so callers can dispose and reuse the Activity.
Event and Context methods should accept the Activity? as their first parameter and typically return void.

Tags and baggage

Use [Tag] and [Baggage] on parameters to control how values are attached — see Tags, Baggage, and Parameter Attributes.

Naming

The ActivitySource name defaults to the assembly name with casing preserved. Set [ActivitySource("MyApp")] to override. v4+ converts tag/baggage keys to snake_case by default; revert with [assembly: TelemetryGeneration(NamingConvention = NamingConvention.Legacy)].

Checklist

Add the Purview.Telemetry.SourceGenerator package.
Create the [ActivitySource] interface (or run the ActivitySource refactoring).
Replace ActivitySource fields and StartActivity/AddEvent/SetTag/SetBaggage calls with the interface.
Register with services.Add{InterfaceNameWithoutI}().
Rebuild and review the Diagnostics.

Next steps

Refactorings — the shipped IDE conversions
Activities — full attribute reference
Multi-Targeting — combine with Logging and Metrics