TaskHub.Shared

Pipeline Lifecycle: Pre, Trans, and Post

The TaskHub.Shared command pipeline defines three distinct stages for behaviors. Understanding the lifecycle is crucial for implementing cross-cutting concerns correctly.

1. IPreBehavior<TCommand, TResult>

Pre-behaviors are executed before the handler. They follow the classic middleware pattern.

Interface

public interface IPreBehavior<TCommand, TResult>
    where TCommand : ICommand
    where TResult : Result
{
    Task<TResult> HandleAsync(
        TCommand command, 
        Func<TCommand, CancellationToken, Task<TResult>> next, 
        CancellationToken ct);
}

Responsibility

• Validation: Check if the command is valid before reaching the handler.
• Logging/Tracing: Start a log context or add tags to the current activity.
• Security: Verify if the user has permission to execute the command.
• Caching: Check if a cached result exists and return it immediately (short-circuiting).

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2. IPostTransformer<TCommand, TResult>

Post-transformers are executed after the handler and all pre-behaviors have completed, but before the result is returned to the caller.

Interface

public interface IPostTransformer<TCommand, TResult>
    where TCommand : ICommand
    where TResult : Result
{
    Task<TResult> HandleAsync(
        TCommand command,
        TResult current,
        Func<TCommand, TResult, CancellationToken, Task<TResult>> next,
        CancellationToken ct);
}

Responsibility

• Result Enveloping: Wrap the handler’s result in a specific DTO format.
• Data Masking: Remove sensitive information from the result based on user permissions.
• Error Mapping: Transform internal error codes into public-facing ones.

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3. IPostBehavior<TCommand, TResult>

Post-behaviors are executed after the final result has been determined (including transformations). They are intended for side-effects.

Interface

public interface IPostBehavior<in TCommand, in TResult>
    where TCommand : ICommand
    where TResult : Result
{
    Task<Result> HandleAsync(TCommand command, TResult result, CancellationToken ct);
}

Responsibility

• Auditing: Record the command and its result in an audit log.
• Event Publishing: Dispatch domain events or integration events.
• Notifications: Trigger emails or push notifications based on the result.

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Summary Table

Stage	Can Short-circuit?	Can Modify Result?	Execution Order
Pre	Yes	Yes (by returning own result)	Outer to Inner (Low Order to High)
Trans	No (next is mandatory)	Yes	Inner to Outer (Low Order to High)
Post	No	No	Sequential (Low Order to High)

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