Use IObserver<BrokerMessage>

[grahamehorner]

@ianrufus nice article and example IMHO I would have passed an IObserver<BrokerMessage> to the ServiceListener instead of the Action<BrokerMessage> as this would allow greater flexibility and the Observering/receiving code to perform linq queries on the message streams.

[jeans-lijian]

When there are more warehouses in a project, the unit of work file becomes very large,How to deal with ？