Umbral Signals

Some reactions don't belong in the code that triggers them. When an order is placed you might want to bust a cache, write an audit line, and ping a channel — but none of that should clutter the "save the order" path. Umbral Signals lets you hang behaviour off events without touching the write code: subscribe to pre/post save/update/delete, or emit your own named events, and react elsewhere. Handlers run outside the registry lock, so a slow subscriber can't throttle every write.

Install

cargo add umbral-signals

Wire it up

use umbral::prelude::*;
use umbral_signals::SignalsPlugin;

let app = App::builder()
    .database("default", pool)
    .plugin(SignalsPlugin)
    .build()?;

Target: react to a domain event

Emit a named event where it happens; subscribe wherever the reaction lives.

use umbral_signals::{emit, subscribe_async};

// at startup:
subscribe_async("order_placed", |payload| async move {
    let order_id = payload["id"].as_i64().unwrap_or(0);
    bust_cache(order_id).await;
});

// in the handler:
emit("order_placed", serde_json::json!({ "id": order.id })).await;

For work that must survive a crash, have the handler enqueue an umbral-tasks job.

What you get

• Pre/post save/update/delete model lifecycle signals
• Emit and subscribe to your own named events
• Handlers run outside the registry lock — slow ones don't block writes
• #[umbral(signal_skip)] keeps secrets / PII out of the payload
• Pair with umbral-tasks for durable, crash-safe reactions