C# negate an expression

Question

I'm seeking for a way to negate an expression used to filter IQueryable sequences.

So, I've got something like:

Expression<Func<T, bool>> expression = (x => true);

Now I wish to create the expression which would result in yielding (x => false) - so I basically want to negate the expression.

The working method I've found myself works like this:

var negatedExpression = 
   Expression.Lambda<Func<T, bool>> (Expression.Not(expression.Body),
                                     expression.Parameters[0])));

But I'm almost sure there is a better way - could you help me? (something like Not(expression), probably).

Answer 1

An easy extension method:

public static Expression<Func<T, bool>> Not<T>(this Expression<Func<T, bool>> one)
{
    var candidateExpr = one.Parameters[0];
    var body = Expression.Not(one.Body);

    return Expression.Lambda<Func<T, bool>>(body, candidateExpr);
}

Usage:

Expression<Func<int, bool>> condition = x => x > 5;
var source = Enumerable.Range(1, 10);
var result1 = source.Where(condition.Compile());   //6,7,8,9,10
var result2 = source.Where(condition.Not().Compile());    //1,2,3,4,5