C#•4y ago

Help with Implicit Explicit operators

This is my operator definition

public static implicit operator EventViewModel(Entry e)
        {
            EventViewModel viewModel = new EventViewModel();
            viewModel.Id = e.Id;
            viewModel.Title = e.Title;
            viewModel.StartDate = e.DateStart;
            viewModel.EndDate = e.DateEnd;
            return viewModel;
        }

public static implicit operator EventViewModel(Entry e)
        {
            EventViewModel viewModel = new EventViewModel();
            viewModel.Id = e.Id;
            viewModel.Title = e.Title;
            viewModel.StartDate = e.DateStart;
            viewModel.EndDate = e.DateEnd;
            return viewModel;
        }

public static implicit operator EventViewModel(Entry e)
        {
            EventViewModel viewModel = new EventViewModel();
            viewModel.Id = e.Id;
            viewModel.Title = e.Title;
            viewModel.StartDate = e.DateStart;
            viewModel.EndDate = e.DateEnd;
            return viewModel;
        }

public static implicit operator EventViewModel(Entry e)
        {
            EventViewModel viewModel = new EventViewModel();
            viewModel.Id = e.Id;
            viewModel.Title = e.Title;
            viewModel.StartDate = e.DateStart;
            viewModel.EndDate = e.DateEnd;
            return viewModel;
        }

I've not been able to find the exacts. With this definition, will it convert from Entry to ViewModel or ViewModel to Entry? Because, with the said implementation, following conversion doesn't work:

EventData = Context.Entries.Where(e => e.UserId == UserId);

EventData = Context.Entries.Where(e => e.UserId == UserId);

EventData = Context.Entries.Where(e => e.UserId == UserId);

EventData = Context.Entries.Where(e => e.UserId == UserId);
The error is Can't convert from IQueryable<Entry> to IQueryable<ViewModel>

canton7•11/1/22, 2:36 PM

It converts an

Entry

Entry

to a EventViewModelEventViewModel, but that doesn't mean you'll get an automatic conversion from an IQueryable<Entry>IQueryable<Entry> to an IQueryable<EventViewModel>IQueryable<EventViewModel>

Alex FrostOP•11/1/22, 2:36 PM

Alex FrostOP•11/1/22, 2:37 PM

So what's the way to do that

canton7•11/1/22, 2:37 PM

Particularly as this is going up to a database, and the database has no idea how to run your user-defined conversion

canton7•11/1/22, 2:37 PM

.Select(x => (EventViewModel)x).Select(x => (EventViewModel)x)? You need something to convert each element to an EventViewModelEventViewModel

Alex FrostOP•11/1/22, 2:38 PM

Right I used Select but wanted to automate it a bit

canton7•11/1/22, 2:38 PM

Although at that point you might as well drop the operator, as it really is code smell, and just do .Select(x => new EventViewModel(x)).Select(x => new EventViewModel(x))

Alex FrostOP•11/1/22, 2:39 PM

.Select(x => new EventViewModel(x)).Select(x => new EventViewModel(x)) that seems like a constructor, so I'll have to implement a constructor for ViewModel, right?

canton7•11/1/22, 2:39 PM

Yeah, that'll be neater than an implicit conversion

Tvde1•11/1/22, 2:40 PM

In my projects, we make an extension method .ToDto().ToDto() or sorts and then do

query.Select(x => x.ToDto())

query.Select(x => x.ToDto())

To map from entities to DTOs

Alex FrostOP•11/1/22, 2:40 PM

Perfect, thanks a bunch you guys

Help with Implicit Explicit operators

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