Expression tree - not contains

Question

I need to create an Expression to search one string not contains another. I was able to create it for contains method:

return Expression.Call(firstOrDefaultCall, typeof(string).GetMethod("Contains"), Expression.Constant(text));

how to convert it to 'not contains'?

Answer 1

How would you normally write it?

var stringValue = "foo"
var result = !stringValue.Contains("o");

Notice the logical negation operator ! before Contains(). That's the only part you are missing. To negate a boolen value when building an expression, use Expression.Not():

return Expression.Not(
    Expression.Call(
        firstOrDefaultCall, 
        typeof(string).GetMethod("Contains"), 
        Expression.Constant(text)));

And don't fall into trap of using Expression.Negate(). That one is for an arithmetic negation operation, example of arithmetic negation:

var negatedPi = Math.PI * -1;