Linq PredicateBuilder with conditional AND, OR and NOT filters

Question

We have a project using LINQ to SQL, for which I need to rewrite a couple of search pages to allow the client to select whether they wish to perform an and or an or

Answer 1

If you are looking for less lines you can replace the if/else with ternary operator:

query = SearchType == SearchType.And ? PredicateBuilder.True<Job>() : PredicateBuilder.False<Job>();

   foreach (var predicate in predicates)
   {
        query = SearchType == SearchType.And ? query.And(predicate) : query.Or(predicate);
   }

for the 'and not' / 'or not' part the ! operator should do the trick.

PD: Did you test the foreach part is correctly setting the predicates?, as far as i remember you are building the expression that will be executed at later point in time, so you may have a literal reference just to the last set predicate in the final iteration, and that's why you must use a temp variable to save the value of each iteration.

EDIT: If you want to negate a expression programmatic, that's a tricky one, you can try something like:

internal static Expression<Func<Job, bool>> Description(string term, bool invert)
        {
           return NegateExp<Func<Job, bool>>(p => p.Description.Contains(term), invert);
        }

And the NegateExp method will be something like:

public static Expression<TDelegate> NegateExp<TDelegate>(Expression<TDelegate> expression, bool inverse)
        {
            if (inverse)
            {
                return Expression.Lambda<TDelegate>(Expression.Not(expression.Body), expression.Parameters);
            }
            return expression;
        }

You can take a look at this question for more examples Is there any way to negate a Predicate?