Case In Lambda Expression

Question

I wrote a method which calls a method that returns a linq query. Inside this method, I need to apply a case expression to the linq query I'm receiving from the method I call. I thought that maybe with a lambda expression it would be possible to apply a case expression, but how can I do this?

Answer 1

Well, you can use a statement body lambda expression:

Func<int,string> x = value =>
{
    switch(value)
    {
        case 0: return "hello";
        case 1: return "there";
        default: return "other";
    }
};

However, you won't be able to convert that into an expression tree, as they only support lambda expressions with a single expression. Are you trying to use LINQ to SQL here?

Of course, you could use nested conditionals instead, and that should work with expression trees:

Expression<Func<int,string>> x = value =>
    value == 0 ? "hello"
    : value == 1 ? "there"
    : "other";

It's a sort of switch/case... although not terribly efficient, it might be good enough for you.

Answer 2

You might be able to use the ternary statement.

[boolean expression] ? [result if true] : [result if false]

Answer 3

Can you use a plain old function to accomplish this instead of a lambda?

X.Select( GetY );

or

X.Select( x => GetY(x) );

or

from x in X
select new
{
   y = GetY(x)
};

...

private YType GetY( XType x )
{
    switch( x )
    {
       ...
    }
}