snapshot of https://github.com/ThreeDotsLabs/watermill.git (master, 2026-09-15; blobs > 131072B omitted)

UPGRADE-0.4.md

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+# UPGRADE FROM 0.3.x to 0.4
+
+## `watermill/components/cqrs`
+
+### `CommandHandler.HandlerName` and `EventHandler.HandlerName` was added to the interface.
+
+If you are using metrics component, you may want to keep backward capability with handler names. In other cases, you can implement your own method of generating handler name.
+
+Keeping backward capability for **event handlers**:
+
+```
+func (h CommandHandler) HandlerName() string {
+    return fmt.Sprintf("command_processor-%s", h)
+}
+```
+
+Keeping backward capability for **command handlers**:
+
+```
+func (h EventHandler) HandlerName() string {
+    return fmt.Sprintf("event_processor-%s", ObjectName(h))
+}
+```
+
+### Added `CommandsSubscriberConstructor` and `EventsSubscriberConstructor`
+
+From now on, `CommandsSubscriberConstructor` and `EventsSubscriberConstructor` are passed to constructors in CQRS component.
+
+They allow creating customized subscribers for every handler. For usage examples please check [_examples/cqrs-protobuf](_examples/cqrs-protobuf).
+
+
+### Added context to `CommandHandler.Handle`, `CommandBus.Send`, `EventHandler.Handle` and `EventBus.Send`
+
+Added missing context, which is passed to Publish function and handlers.
+
+### Other
+
+- `NewCommandProcessor` and `NewEventProcessor` now return an error instead of panic
+- `DuplicateCommandHandlerError` is returned instead of panic when two handlers are handling the same command
+- `CommandProcessor.routerHandlerFunc` and `EventProcessor.routerHandlerFunc` are now private
+- using `GenerateCommandsTopic` and `GenerateEventsTopic` functions instead of constant topic to allow more flexibility
+
+
+## `watermill/message/infrastructure/amqp`
+
+### `Config.QueueBindConfig.RoutingKey` was replaced with `GenerateRoutingKey`
+
+For backward compatibility, when using the constant value you should use a function:
+
+
+```
+func(topic string) string {
+    return "routing_key"
+}
+```
+
+
+## `message/router/middleware`
+
+- `PoisonQueue` is now `PoisonQueue(pub message.Publisher, topic string) (message.HandlerMiddleware, error)`, not a struct
+
+
+## `message/router.go`
+
+- From now on, when all handlers are stopped, the router will also stop (`TestRouter_stop_when_all_handlers_stopped` test)