OfType预制件而不是过滤器

Question

Let's say in my database I have 2 classes: Class FooBar and Class BarFoo. I perform a query on my database which returns class FooBos which contains a list of FooBar BUT the list can contain instances of BarFoo(don't ask me why , this how i got the database and i can't edit it).

Anyway to build my Domain object I do a check to see which class is which using following code

if(FooBos.FooBars.OfType<BarFoo>().Count() != 0)
  //Do things for FooBar here
else
  //Do Things for BarFoo here

So the problem is after the OfType the entire list is of the Type BarFoo and i can't seem to figure out why.

Anyone knows why this happens ?

Answer 1

Generally, OfType<> is employed whenever an inheritance relation exists. In your case, I suspect that FooBar is a child of BarFoo.

If this is the case then it means all of your objects in the list is either inherit BarFoo or they are just BarFoo objects; so OfType<BarFoo> returns all objects.

Answer 2

If you don't mind iterating twice (using Linq), you can use two separate statements:

foreach (BarFoo barfoo in FooBos.FooBars.OfType<BarFoo>()
    // Do something with barfoo

foreach (FooBar foobar in FooBos.Foobars.OfType<FooBar>()
    // Do something with foobar

Otherwise you'll have to do it in a single loop the long way:

foreach (var entry in FooBos.FooBars)
{
    BarFoo barfoo = entry as BarFoo;

    if (barfoo != null)
    {
        // Do something with barfoo
    }
    else
    {
        FooBar foobar = entry as FooBar;

        if (foobar != null)
        {
            // Do something with foobar
        }
    }
}