Question

I’m trying to put together a ViewModel that will have a list of users and each user will have a list of locations.
The User table and Location table are joined together through another table that holds each respective ID and some other information. This table is essentially a many to many join table.
I’ve tried a few different viewModel approaches and they we’re severely lacking… What would be the best approach for displaying this type of information?

Answer 1

I assume that the issue is that you want to be able to access the collection by either User or Location. One approach could be to use ILookup<> classes. You’d start with the many-to-many collection and produce the lookups like this:

var lookupByUser = userLocations.ToLookup(ul => ul.User);
var lookupByLocation = userLocations.ToLookup(ul => ul.Location);

Update:

Per your description, it seems like you don’t really need to have a full many-to-many relationship in your ViewModel. Rather, your ViewModel could have a structure like this:

public class YourViewModel
{
    public IEnumerable<UserViewModel> Users { get; set; }
}

public class UserViewModel
{
    // User-related stuff

    public IEnumerable<LocationViewModel> Locations { get; set; }
}

If you wanted to avoid redundant LocationViewModel objects, you could pre-build a mapping between your Model and ViewModel objects:

var locationViewModels = myLocations.ToDictionary(
    loc => loc, loc => CreateLocationViewModel(loc));

And then reuse these objects when populating your page’s ViewModel.