Jul 4, 2018 · Jul 4, 2018 · Dec 8, 2018 · Nov 7, 2018
diff --git a/messenger/multiple-buses.rst b/messenger/multiple-buses.rst
 .. index::
    single: Messenger; Multiple buses

 Multiple Buses
 ==============

 A common architecture when building application is to separate commands from
 queries. Commands are actions that do something and queries fetches data. This
 is called CQRS (Command Query Responsibility Segregation). See Martin Fowler's
 `article about CQRS`_ to learn more. This architecture could be used together
 with the messenger component by defining multiple buses.

 A **command bus** is a little different form a **query bus**. As example,
 command buses must not return anything and query buses are rarely asynchronous.
 You can configure these buses and their rules by using middlewares.

 It might also be a good idea to separate actions from reactions by introducing
 an **event bus**. The event bus could have zero or more subscribers.

 .. configuration-block::

    .. code-block:: yaml

        framework:
            messenger:
                default_bus: messenger.bus.command
                buses:
                    messenger.bus.command:
                        middleware:
                            - messenger.middleware.validation
                            - messenger.middleware.handles_recorded_messages: ['@messenger.bus.event']
                            - doctrine_transaction_middleware: ['default']
                    messenger.bus.query:
                        middleware:
                            - messenger.middleware.validation
                    messenger.bus.event:
                        middleware:
                            - messenger.middleware.allow_no_handler
                            - messenger.middleware.validation

 .. _article about CQRS: https://martinfowler.com/bliki/CQRS.html
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,41 @@
		.. index::
		single: Messenger; Multiple buses

		Multiple Buses
		==============

		A common architecture when building application is to separate commands from
		queries. Commands are actions that do something and queries fetches data. This
		is called CQRS (Command Query Responsibility Segregation). See Martin Fowler's
		`article about CQRS`_ to learn more. This architecture could be used together
		with the messenger component by defining multiple buses.

		A command bus is a little different form a query bus. As example,
		command buses must not return anything and query buses are rarely asynchronous.
		You can configure these buses and their rules by using middlewares.

		It might also be a good idea to separate actions from reactions by introducing
		an event bus. The event bus could have zero or more subscribers.
Copy link Contributor magnusnordlanderDec 8, 2018 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. If we're mentioning that events have zero or more subscribers, we should probably mention that commands and queries have exactly one handler.

		.. configuration-block::

		.. code-block:: yaml

		framework:
		messenger:
		default_bus: messenger.bus.command
		buses:
		messenger.bus.command:
		middleware:
		- messenger.middleware.validation
		- messenger.middleware.handles_recorded_messages: ['@messenger.bus.event']
		- doctrine_transaction_middleware: ['default']
		messenger.bus.query:
		middleware:
		- messenger.middleware.validation
		messenger.bus.event:
		middleware:
		- messenger.middleware.allow_no_handler
Copy link Contributor ogizanagiNov 7, 2018 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. In 4.2,`default_middleware: allow_no_handlers` must be used instead. (https://github.com/symfony/symfony/blob/master/UPGRADE-4.2.md#frameworkbundle)
		- messenger.middleware.validation

		.. _article about CQRS: https://martinfowler.com/bliki/CQRS.html