Question

What do you think about putting Get-logic in the getters of a ViewModel? Something like:

public class DummyViewModel
{
    public int Id { get; set; }

    private DummyObject myObject;

    public DummyObject MyObject
    {
        get
        {
            if (MyObject == null)
            {
                DummyRepository repo = new DummyRepository();
                myObject = repo.Get(Id);
            }
            return myObject;
        }
    }

}

Is this bad practice, or totally fine? I find my controllers getting really bloated by doing all the get-logic there, but I’m really torn as to where I should put it…

My reason for doing it this way, is that I can pass the ViewModel to different types of view, and only the neccessary DB-lookup will be performed based on what property is requested.

Answer 1

There is nothing wrong with putting logic in getters in VMs – the role of a VM is to present data to a view, and it should be as ready to “view” as possible (the View should not be having to do too much (if any) work to shape the data before showing it).

As an example, I use properties called GetAvailableClients in my VM, and that will be one of the properties that the View binds to. The job of that particular getter is to filter data – IOW present a reduced set of data selected from a complete list (which is also held in the VM), that data will usually be filtered using LINQ, which means I have placed some custom logic in the getter.

What I am not a fan of though is the rest of your approach, where if the property hasn’t been filled it goes off to the repository and gets the data itself. To me that is a no-no, the property is totally violating the principle of single responsibility by making the property responsible for too much. Not to mention that is not a good practice to follow once you start binding that property to the UI – suddenly your app will start hanging when the user performs an action because your property getter has been triggered and it has decided to make a call to the database or a webservice, and to make it worse that call has been done on the UI thread…. it just gets ugly.