C#•3y 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;
        }

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); The error is Can't convert from IQueryable<Entry> to IQueryable<ViewModel>

9 Replies

canton7•3y ago

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

Alex FrostOP•3y ago

🙁 So what's the way to do that

canton7•3y ago

Particularly as this is going up to a database, and the database has no idea how to run your user-defined conversion .Select(x => (EventViewModel)x)? You need something to convert each element to an EventViewModel

Alex FrostOP•3y ago

Right I used Select but wanted to automate it a bit

canton7•3y ago

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))

Alex FrostOP•3y ago

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

canton7•3y ago

Yeah, that'll be neater than an implicit conversion

Tvde1•3y ago

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

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

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

To map from entities to DTOs

Alex FrostOP•3y ago

Perfect, thanks a bunch you guys 🙂

Gaming

Programming

Help with Implicit Explicit operators