Show ow to configure a doctrine transaction middleware

Author: Nyholm

messenger/working-with-doctrine.rst

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+.. index::
+    single: Messenger; Working with Doctrine
+
+Working with Doctrine
+=====================
+
+If your message handlers writes to a database it is a good idea to wrap all those
+writes in a single Doctrine transaction. This make sure that if one of your database
+query fails, then all queries are rolled back and give you a change to handle the
+exception knowing that your database was not changed by your message handler.
+
+To make sure your message bus wraps the handler in one transaction you must first
+register the middleware as a service.
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # config/services.yaml
+        services:
+            app.messenger.middleware_factory.transaction:
+                class: Symfony\Bridge\Doctrine\Messenger\DoctrineTransactionMiddlewareFactory
+                arguments: ['@doctrine']
+
+            app.doctrine_transaction_middleware:
+                class: Symfony\Bridge\Doctrine\Messenger\DoctrineTransactionMiddleware
+                factory: ['@app.messenger.middleware_factory.transaction', 'createMiddleware']
+                abstract: true
+                arguments: ['default']
+
+Next thing you need to do is to add the middleware to your bus configuration.
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # config/packages/messenger.yaml
+        framework:
+            # ...
+            default_bus: messenger.bus.command
+            buses:
+                messenger.bus.command:
+                    middleware:
+                        - messenger.middleware.validation
+                        - app.doctrine_transaction_middleware: ['default']