Question

I like the idea of Command Query Separation but can’t see how to use it within an MVC Controller action which is adding an entity, and needs the new entity’s ID after adding it.

For example, in the simplified example below a service is used to create a new item:

public ActionResult Assign(AssignViewModel viewModel)
{
     var newItem = _AssignItemService.AssignItem(viewModel.ItemName, viewModel.ItemValue);

     return RedirectToAction("ListItem", new {id = newItem.Id);
}

But when I redirect to the action which is going to display the new item, I need to know the ID of the newly created item, in order that it can be retrieved from the database. So I have to ask the service to return the newly created item (or at least, its ID).

In pure CQS, a command has no return value, so the pattern above would be invalid.

Any advice gratefully received.

Answer 1

You should pass to AssignItem method an instance of “Item” (or whatever your entity’s name is) that is created from the viewmodel’s values, then the method doesnt have to return anything, instead it will just update entity’s Id property making it a Command method.

You can then use entity.Id for anything you want