Can I Access Models and Services in my Mediators?
To promote loose coupling your mediators can listen for system events that will be dispatched by Service and Model classes. By listening for events, your mediators do not need to be interested in where these events originate from, they just make use of the strongly typed payload the event carries with it. For this purpose, multiple mediators can be listening for the same event, adjusting their state according to the data that they have received.
Directly accessing services through a mediator can provide convenience, without serious risk of coupling. A service is not storing data, simply providing an API for making requests to an external service and receiving the response. Being able to access this API directly can save your application from unnecessary command classes to achieve the same goal. If the service API is repeatedly accessed in the same way from many mediators, it can be beneficial to encapsulate this behavior in a command to keep the behavior consistent and reduce the repetition of injecting the service and accessing it directly in your mediators.
Reference MVCS Implementation