Which is the right place to call service in MVVM pattern, View Model or Model? I am planning to invoke service from ViewModel, get the JSON and convert it to corresponding model. The reason I am not invoking service from Model to keep the Model decoupled from service.
Is this approach right or I should call service from Model?
Typically VM is responsible for making service calls. A sample call stack can be:
UI Event (View) => ICommand Execute (VM) => Service Call (VM).
It's advisable to have a re-usable Service Tier utilising the same domain objects as your app - as it allows the service-calling logic to be shared by multiple VMs (added from comments).
I think that the right place for calling a service is in Model.
The reason I am not invoking service from Model to keep the Model decoupled from service
So in this case you have your ViewModel which should handle presentation logic coupled with Service calls that probably involve data validation or manipulation. According to
5: Implementing the MVVM Pattern Using the Prism Library 5.0 for WPF
The View Model Class:
It encapsulates the presentation logic required to support a use case or user task in the application. The view model is testable independently of the view and the model. The view model typically does not directly reference the view. It implements properties and commands to which the view can data bind. The view model coordinates the view's interaction with the model. It may convert or manipulate data so that it can be easily consumed by the view and may implement additional properties that may not be present on the model.
The Model Class
Model classes are non-visual classes that encapsulate the application's data and business logic. They are responsible for managing the application's data and for ensuring its consistency and validity by encapsulating the required business rules and data validation logic. The model classes are typically used in conjunction with a service or repository that encapsulates data access and caching.
And as the previous answer showed something like this:
UI Event (View) => ICommand Execute (VM) => Service Call (VM).
I think it should be more like this
UI Event (View) => ICommand Execute (VM) => Handle Command/Action (VM) => Execute business/data logic that VM Command should have triggered (M) => Service Call (M).
You can create some kind of service helper that can be called from various models if you want to reuse service access code.
