Question

I am trying to write a Linq expression that checks against property in a derived class, but the list is made up of members from a base class. Example code below. The 2nd line of the Process method starting with ‘var list’ does not compile, but I am not sure what syntax I should use to make it valid?

public class Manager
{
    public void Process()
    {
        Base[] stuff = { new Derived() { Id = "1", Name = "me" } };

        var list = stuff.Where<Derived>(d => d.Name == "me");
    }
}

public class Base
{
    public string Id { get; set; }
}

public class Derived : Base
{
    public string Name { get; set; }
}

Answer 1

If you know the list has only Derived, you can use the Cast<T> method:

var list = stuff.Cast<Derived>().Where(d => d.Name == "me");

If there are only some Derived, you can use OfType<T>:

var list = stuff.OfType<Derived>().Where(d => d.Name == "me");

In that case, the non-Derived objects will be skipped.