Messages as Interfaces

Component: NServiceBus

NServiceBus support using interfaces as messages types.

Using interfaces allows "multiple inheritance" where one message can inherit from varieties of other messages. This is useful for solving certain "message evolution" scenarios.

Imagine that the business logic represents a state machine with states X and Y. When the system gets into state X, it publishes the message EnteredStateX. When the system gets into state Y, it publishes the message EnteredStateY. (For more information on how to publish a message, see below.)

In the next version of the system, a new state Z is added, which represents the co-existence of both X and Y states. This can be achieved by defining a message EnteredStateZ which would inherits both EnteredStateX and EnteredStateY.

When the system publishes the EnteredStateZ event, the clients that are subscribed to either of EnteredStateX or EnteredStateY are notified.

The following serializers do not support messages defined as interfaces:

Without the ability to inherit a message from other message types, composition techniques would be required, thereby preventing the infrastructure from automatically routing messages to pre-existing subscribers of the composed messages.

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