how to Shim Enumerable Cast In Unit Test

Question

I used in EF Expression Like this,

query
    .Select(item => new
    {
        DoubleValue =
            new List<string>() { item.AdmissionTicketCode }
                .Cast<double>()
                .FirstOrDefault()
    })
    .ToList();

but, run at Unit Test it thorw an error "Specified Cast Is Not Valid".

how do I deal this problem

System.Linq.Enumerable ScreenShot

I tried to add System.Linq.Fakes、and wanted use ShimEnumerable to resolve it, but it does not exist in System.Linq.Fakes.

Answer 1

.Cast<double>() is a NOP on a double and will throw on any other type. Also, keep in mind, that a cast is not a conversion. If item.AdmissionTicketCode is a string then you need to parse it, not cast it.

So let's break down what you might need to do.

Your current code is equivalent to:

query
    .Select(item => new
    {
        DoubleValue = (double)item.AdmissionTicketCode
    })
    .ToList();

Assuming that item.AdmissionTicketCode is a string then the compiler lets us know it's a bad cast right now.

So it should be like this:

query
    .Select(item => new
    {
        DoubleValue = double.Parse(item.AdmissionTicketCode)
    })
    .ToList();

It's a bit pointless having a single property in an anonymous type, so you could go one step further:

query
    .Select(item => double.Parse(item.AdmissionTicketCode))
    .ToList();

---

If EF doesn't support double.Parse then do this:

query
    .Select(item => item.AdmissionTicketCode)
    .ToList()
    .Select(x => double.Parse(x))
    .ToList();