Question

In my mvc site I use EF 4.1 for data access . Now I develop product search functionality. The method signature for getting filtered products is:

PagedList<Dress> GetDressesPage<TKey>(int page, int dressesPerPage, Func<Dress, bool> selection, Func<Dress, TKey> order, SortDirection direction);

and the way in which I get the products is:

dresses = _context.Dresses.Where(selection).OrderBy(order).Skip(page * dressesPerPage).Take(dressesPerPage).ToList();

The problem is with the function selection. I would like to be able to construct that by appending different conditions. Now I am constructing that using some if clauses for each combination of parameters … but that gets too complex.

Do you know a simpler way in which I could pass a filter as a parameter?

Answer 1

Use the Predicate Builder. Replace the Func<Dress, bool> with Expression<Func<Dress, bool>>. Otherwise the queries will turn into LINQ-to-Objects.

  var predicate = PredicateBuilder.True<Dress>();
  if (!string.IsNullOrEmpty(name))
  {
       predicate = predicate.And(d => d.Name.Contains(name));
  }

  dresses = _context.Dresses.Where(predicate).OrderBy(order)
      .Skip(page * dressesPerPage).Take(dressesPerPage).ToList();