Question

I want to know if a type is IQueryable.

var t = typeof(IQueryable<int>);
bool isQueryable = (t is IQueryable); // false
bool isAssignableFrom = t.IsAssignableFrom(typeof(IQueryable)); // false
bool nameStartsWithIQueryable = t.Name.StartsWith("IQueryable"); // true

The third way – looking at the beginning of the type name – works but feels like a hack.

Is there another way to accomplish this?

Answer 1

Use GetGenericTypeDefinition:

bool isQueryable = t.GetGenericTypeDefinition() == typeof(IQueryable<>);

If you need to handle deeper ancestries (where you are checking aganist the base type), you can write a helper method:

public static bool IsType(Type type, Type ancestor)
{
    while (type != null)
    {
        if (type.IsGenericType)
            type = type.GetGenericTypeDefinition();
        if (type == ancestor)
            return true;
        type = type.BaseType;
    }
    return false;
}

Calling it like so:

bool isQueryable = IsType(typeof(IQueryable<int>), typeof(IQueryable<>));

(Note that this won’t help with base types that implement other interfaces, since checking against that would require a lot more code using Type.GetInterfaces recursively.)