Dispatch Module¶

The Dispatch module generates strongly-typed command and query dispatch methods from decorated handler methods — zero indirection, method overload resolution IS the dispatch. The generator emits one typed overload per handler, so the C# compiler picks the right one at the call site. Full type safety, no runtime lookup, no mediator pattern.

Quick Start¶

Define command/query records, write handler methods, and mark a static partial class as the dispatch entry point:

using Deepstaging.Dispatch;
using LanguageExt;

// 1. Define a command
public record CreateOrder(string Name, int Quantity) : ICommand;
public record OrderCreated(string Id);

// 2. Write a handler
public static class OrderCommands
{
    [CommandHandler]
    public static Eff<AppRuntime, OrderCreated> Handle(CreateOrder cmd) =>
        from _ in OrderStore.SaveAsync<AppRuntime>(new Order(cmd.Name, cmd.Quantity))
        select new OrderCreated("123");
}

// 3. Mark the dispatch module
[DispatchModule]
public static partial class AppDispatch;

The generator produces typed dispatch methods on AppDispatch:

// Dispatch via the command record
var result = await AppDispatch.Dispatch(new CreateOrder("Widget", 5))
    .RunAsync(runtime);

// Or use the convenience overload
var result = await AppDispatch.CreateOrder("Widget", 5)
    .RunAsync(runtime);

Features¶

Feature	Description
Typed dispatch	One overload per handler — C# compiler resolves the route
Commands & Queries	`ICommand` / `IQuery` marker interfaces
Auto-commit	`IAutoCommittable.CommitAsync()` called after command handlers (configurable)
Validation	Applicative validation with `FieldError` and structured 422 responses
Authorization	`[Authorize]` on handlers with `[AuthPolicies]` integration
Idempotency	`[Idempotent]` enforces unique processing per idempotency key
Rate limiting	`[RateLimit("policy")]` applies named rate limit policies to handlers
Convenience overloads	`AppDispatch.CreateOrder(name, qty)` alongside `Dispatch(cmd)`
Tracing	OpenTelemetry activity per dispatch

What's Next¶

Page	Description
Attributes	`[DispatchModule]`, `[CommandHandler]`, `[QueryHandler]`, `[Authorize]`, marker interfaces
Generated Code	Pipeline steps, result types, convenience overloads, tracing, auditing
Effects Composition	How handlers return `Eff<RT, T>`, runtime constraints, composing with `[Runtime]` and `[Uses]`
Validation	Applicative validation with `FieldError`, `ValidatorType`, and structured 422 responses
Authorization	`[AuthPolicies]`, `[AuthPolicy]`, RBAC with `[Permissions]`/`[Roles]`/`[Require]`, ASP.NET integration

Diagnostics¶

ID	Severity	Description
DSDSP01	Error	DispatchModule class must be partial
DSDSP02	Error	DispatchModule class must be static
DSDSP03	Error	CommandHandler method must be static
DSDSP04	Error	QueryHandler method must be static
DSDSP05	Warning	CommandHandler has invalid signature (must return `Eff<RT, T>` with ≥1 parameter)
DSDSP06	Warning	QueryHandler has invalid signature (must return `Eff<RT, T>` with ≥1 parameter)
DSDSP07	Error	ValidatorType is missing a `Validate` method with the correct signature
DSDSP08	Error	AuthPolicies class must be `static partial`
DSDSP09	Error	AuthPolicy method must be `static bool (ClaimsPrincipal)`
DSDSP10	Error	`Validated = true` and `ValidatorType` are mutually exclusive
DSDSP11	Warning	`Validated = true` but input type has no DataAnnotations or `Validate` methods
DSDSP12	Error	Custom `Validate{Field}` method returns wrong type
DSDSP13	Info	Input type has validated fields without custom validators
DSDSP14	Warning	Handler has no `[Require]`, `[Authorize]`, or `[Public]` attribute