How to check for nulls in a deep lambda expression? [duplicate]

You could do this with a generic helper extension method, something like:

public static class Get {
    public static T IfNotNull<T, U>(this U item, Func<U, T> lambda) where U: class {
        if (item == null) {
            return default(T);
        }
        return lambda(item);
    }
}

var one = new One();
string fooIfNotNull = one.IfNotNull(x => x.Two).IfNotNull(x => x.Three).IfNotNull(x => x.Four).IfNotNull(x => x.Foo);

You can't do that in a concise way. You can either make the lambda multiple lines, or use nested ternary operators:

var result = GetValue(one, x => x.Two == null ? null :
                                x.Two.Three == null ? null :
                                x.Two.Three.Four == null ? null :
                                x.Two.Three.Four.Foo;

Ugly, I know.

Doing this concisely requires an as-yet-unimplemented operator. We considered adding an operator ".?" to C# 4.0 which would have your desired semantics, but unfortunately it did not fit into our budget. We'll consider it for a hypothetical future version of the language.

You can now do using the Maybe project on codeplex.

Syntax is:

string result = One.Maybe(o => o.Two.Three.Four.Foo);

string cityName = Employee.Maybe(e => e.Person.Address.CityName);