On-Demand Channel Override

Sometimes you need to send to a raw address without having a Notifiable:

• An admin alert to a Slack channel or email address not tied to a user.
• A signup confirmation to an email that doesn't yet have a user record.
• An ad-hoc "send this to myself" from a CLI tool.

For that, use OnDemand:

notifier.SendOnDemand(ctx,
    notification.OnDemand{
        "mail":     "admin@example.com",
        "slack":    "#ops-alerts",
        "whatsapp": "+628123456789",
    },
    IncidentStarted{Severity: "sev-1", Service: "checkout"},
)

How it works

OnDemand is a map[string]any — keys are channel names, values are whatever RouteNotificationFor(channel) would normally return. Internally, go-notification wraps it in an anonymous Notifiable and dispatches exactly like Send().

Picking channels

The notification's Via() is still called and still decides which channels to use. OnDemand only provides routing for those channels. If the notification returns []string{"mail", "database"} but your OnDemand map only has "mail", the database dispatch is skipped (no target).

Per-channel override with existing user

You can also override routing for a single channel while using a regular user:

notifier.SendTo(ctx, user, OnDemand{
    "mail": "custom@example.com", // overrides user.Email for this one send
}, OrderShipped{})

This is less common — most teams find it clearer to model the override explicitly in the user type (e.g. user.NotificationEmail vs user.LoginEmail).

Routes that take complex types

RouteNotificationFor can return any type — []string (FCM token list), numeric IDs (Telegram chat IDs), structs. Same in OnDemand:

notifier.SendOnDemand(ctx,
    OnDemand{
        "push": []string{token1, token2},
        "telegram": int64(123456789),
    },
    Alert{},
)

Use cases that are a bad fit

• High-volume fan-out to dynamic addresses — SendOnDemand works, but creating a real Notifiable will be cleaner and more maintainable.
• Anything you'll call from three or more places — define a proper type once.

Tests

OnDemand is the nicest way to test notifications in isolation — you can assert what Via() and the To*() methods produce without wiring a fake user:

func TestOrderShippedRendering(t *testing.T) {
    notifier, captured := newTestNotifier() // test channel that records calls

    notifier.SendOnDemand(ctx,
        OnDemand{"mail": "test@example.com"},
        OrderShipped{OrderID: "A-1"},
    )

    require.Equal(t, "Your order shipped", captured.Subject)
}