WJb Docs - Intermediate

📤 Fan-out

Fan-out is the pattern where one action starts several independent jobs at the same time.

          ┌─→ Action B
Action A ─┼─→ Action C
          └─→ Action D

The branches run independently and do not wait for each other.

How to Create Fan-out

Return multiple commands from a single action:

return Results.Next(
    JobCommands.Next<LogAction>(
        new LogInput { Message = "Order created" }),
    JobCommands.Next<SendEmailAction>(
        new EmailInput { To = customer.Email }),
    JobCommands.Next<AuditAction>(
        new AuditInput { Event = "order-created" }));

Full Example

[ActionName("create-order")]
public sealed class CreateOrderAction : JobAction<OrderInput>
{
    public override async Task<IActionResult> ExecuteAsync(
        OrderInput input, CancellationToken ct)
    {
        var order = await CreateOrderAsync(input, ct);
return Results.Next(
            JobCommands.Next<SendConfirmationAction>(
                new EmailInput
                {
                    To = order.CustomerEmail,
                    Subject = "Order Confirmation",
                    Body = $"Order {order.Id} received"
                }),
            JobCommands.Next<UpdateInventoryAction>(
                new InventoryInput
                {
                    ProductId = order.ProductId,
                    Quantity = order.Quantity
                }),
            JobCommands.Next<LogAction>(
                new LogInput
                {
                    Message = $"Order {order.Id} created"
                }));
    }
}

Execution Flow

create-order
     ├──→ SendConfirmationAction → Complete
     ├──→ UpdateInventoryAction  → Complete
     └──→ LogAction              → Complete

All three jobs are enqueued at the same time and can run in parallel (subject to available workers).

Important Characteristics

• Order of execution between branches is not guaranteed
• Each branch is a normal independent job
• Failure in one branch does not automatically cancel the others
• Data passed to each branch can be different

When to Use Fan-out

Use fan-out when the follow-up steps are independent:

• Sending notifications through multiple channels
• Logging + auditing
• Updating several systems in parallel
• Starting multiple independent processing pipelines

When Not to Use Fan-out

Avoid fan-out when:

• Steps must run in a specific order
• One step needs the result of another
• You need a single final “all done” signal (use sequential or a joining pattern instead)

Key Point

Fan-out is created simply by returning multiple JobCommands.

It is the explicit way to start parallel work in WJb.