Source Generators

Source Generators

The Strategos.Generators package transforms fluent DSL definitions into type-safe artifacts at compile time.

Generated Artifacts Overview

Artifact	Purpose
Phase Enum	Type-safe enumeration of workflow phases
Commands	Wolverine message types for step transitions
Events	Marten event types for audit trail
Saga Class	Complete Wolverine saga with handlers
State Reducers	Property merge logic based on attributes
DI Extensions	Service registration helpers

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Phase Enum

Generated enumeration representing all workflow phases.

Generation Pattern

For a workflow named process-order with steps ValidateOrder, ProcessPayment, FulfillOrder:

// Generated
public enum ProcessOrderPhase
{
    NotStarted,
    ValidateOrder,
    ProcessPayment,
    FulfillOrder,
    Completed,
    Failed
}

Special Values

Value	Description
NotStarted	Initial state before workflow begins
Completed	Terminal state after successful completion
Failed	Terminal state after failure

---

Commands

Generated Wolverine command types for triggering step execution.

Generation Pattern

// Generated for each step
public record ExecuteValidateOrderCommand(
    [property: SagaIdentity] Guid WorkflowId);

public record ExecuteProcessPaymentCommand(
    [property: SagaIdentity] Guid WorkflowId);

public record ExecuteFulfillOrderCommand(
    [property: SagaIdentity] Guid WorkflowId);

Attributes

Attribute	Purpose
[SagaIdentity]	Links command to saga instance

---

Events

Generated Marten event types for audit trail.

Generation Pattern

// Workflow lifecycle events
public record ProcessOrderWorkflowStarted(Guid WorkflowId, DateTimeOffset Timestamp);
public record ProcessOrderWorkflowCompleted(Guid WorkflowId, DateTimeOffset Timestamp);

// Phase transition events
public record ProcessOrderPhaseChanged(
    Guid WorkflowId,
    ProcessOrderPhase FromPhase,
    ProcessOrderPhase ToPhase,
    DateTimeOffset Timestamp);

// Step completion events
public record ValidateOrderStepCompleted(
    Guid WorkflowId,
    DateTimeOffset Timestamp,
    OrderState StateSnapshot);

Event Properties

Property	Type	Description
WorkflowId	Guid	Workflow instance identifier
Timestamp	DateTimeOffset	When the event occurred
FromPhase	Enum	Previous phase (for transitions)
ToPhase	Enum	New phase (for transitions)
StateSnapshot	TState	State at completion (for step events)

---

Saga Class

Generated Wolverine saga containing all handlers.

Generation Pattern

// Generated saga
public partial class ProcessOrderSaga : Saga
{
    public Guid WorkflowId { get; set; }
    public OrderState State { get; set; }
    public ProcessOrderPhase Phase { get; set; }

    // Entry point
    public async Task<ExecuteValidateOrderCommand> Start(
        StartProcessOrderCommand command,
        CancellationToken ct)
    {
        WorkflowId = command.WorkflowId;
        State = command.InitialState;
        Phase = ProcessOrderPhase.ValidateOrder;
        return new ExecuteValidateOrderCommand(WorkflowId);
    }

    // Step handlers
    public async Task<ExecuteProcessPaymentCommand> Handle(
        ExecuteValidateOrderCommand command,
        ValidateOrderStep step,
        CancellationToken ct)
    {
        var result = await step.ExecuteAsync(State, CreateContext(), ct);
        State = ProcessOrderStateReducer.Reduce(State, result.State);
        Phase = ProcessOrderPhase.ProcessPayment;
        return new ExecuteProcessPaymentCommand(WorkflowId);
    }

    // Additional handlers...
}

Saga Properties

Property	Type	Description
WorkflowId	Guid	Saga identity
State	TState	Current workflow state
Phase	Enum	Current workflow phase

---

State Reducers

Generated logic for merging state updates based on attributes.

Generation Pattern

// For state with [Append] and [Merge] attributes
public static class ProcessOrderStateReducer
{
    public static OrderState Reduce(OrderState current, OrderState update)
    {
        return current with
        {
            // Regular properties: take update value
            Status = update.Status ?? current.Status,
            TotalAmount = update.TotalAmount,

            // [Append] properties: combine lists
            AuditLog = current.AuditLog
                .Concat(update.AuditLog ?? Enumerable.Empty<string>())
                .ToList(),

            // [Merge] properties: combine dictionaries
            Metadata = current.Metadata
                .Concat(update.Metadata ?? new())
                .GroupBy(kv => kv.Key)
                .ToDictionary(g => g.Key, g => g.Last().Value)
        };
    }
}

Merge Behaviors

Attribute	Behavior
(none)	Update replaces current
[Append]	Lists are concatenated
[Merge]	Dictionaries are combined, newer wins

---

DI Extensions

Generated service registration helpers.

Generation Pattern

// Generated extension method
public static class ProcessOrderWorkflowExtensions
{
    public static IServiceCollection AddProcessOrderWorkflow(
        this IServiceCollection services)
    {
        // Register step implementations
        services.AddScoped<ValidateOrderStep>();
        services.AddScoped<ProcessPaymentStep>();
        services.AddScoped<FulfillOrderStep>();

        // Register saga
        services.AddScoped<ProcessOrderSaga>();

        return services;
    }
}

Usage

services.AddStrategos()
    .AddProcessOrderWorkflow();

// Or add all workflows in assembly
services.AddStrategos()
    .AddWorkflowsFromAssembly(typeof(ProcessOrderWorkflow).Assembly);

---

Triggering Generation

Generation is triggered by the [Workflow] attribute on a class containing a workflow definition.

Required Pattern

using Strategos;

namespace MyApp.Workflows;

[Workflow("process-order")]
public static partial class ProcessOrderWorkflow
{
    public static WorkflowDefinition<OrderState> Definition =>
        Workflow<OrderState>.Create("process-order")
            .StartWith<ValidateOrderStep>()
            .Then<ProcessPaymentStep>()
            .Finally<FulfillOrderStep>();
}

Requirements

Requirement	Description
[Workflow] attribute	Triggers source generation
partial modifier	Allows generator to extend class
static modifier	Workflow definitions are static
Namespace	Cannot be in global namespace

---

Generated File Location

Generated files appear in the obj directory and are visible in IDE under Dependencies > Analyzers:

obj/
  Debug/
    net8.0/
      generated/
        Strategos.Generators/
          ProcessOrderWorkflow.g.cs
          ProcessOrderSaga.g.cs
          ProcessOrderStateReducer.g.cs

::: tip Viewing Generated Code In Visual Studio, expand Dependencies > Analyzers > Strategos.Generators to see generated files. In Rider, use Navigate > Generated Code. :::