How to Append to an expression

Question

Based on my question from yesterday:

if I had to append to my existing \'where\' expression, how would i append?

Expression

        

Answer 1

This is a complex scenario. You are almost building your own query engine on top of LINQ. JaredPar's solution (where did it go?) is great if you want a logical AND between all of your criteria, but that may not always be the case.

When I was wrangling with this in one of my project recently, I created two Lists:

List> andCriteria;
List> orCriteria;

(In this case, T is Client, for you)

I would populate the Lists with predicates that I want to be true. For instance,

decimal salRequirement = 50000.00;
andCriteria.Add(c => c.Salary > salRequirement);
orCriteria.Add(c => c.IsMarried);

Then, I would check against all the criteria in the Lists in my Where clause. For instance:

Expression> clientWhere =
    c => andCriteria.All(pred => pred(c) ) && orCriteria.Any(pred => pred(c) );

This could also be done with a for-loop for readability's sake. Remember to use the correct order of operations when applying your OR and AND clauses.