Search and filter in MVC3 Razor using Linq

Question

This code works fine, but I just don't like all the if else. If I keep adding field to filter, it's going to get messy.

I am not using EF and cannot on this.

Controller code:

var books = bookRepository.GetDogs();    
if (!String.IsNullOrEmpty(searchString))
{

    if (!String.IsNullOrWhiteSpace(searchString) && searchGender != String.Empty && searchHand != String.Empty)
    {
        books = books.Where(b => b.Name.ToUpper().Contains(searchString.ToUpper())
                                 && b.Gender == searchGender && b.Handedness == searchHand);
    }
    else if (!String.IsNullOrWhiteSpace(searchGender) && searchString == String.Empty && searchHand == String.Empty)
    {
        books = books.Where(b => b.Gender == searchGender);
    }
    else if (String.IsNullOrWhiteSpace(searchGender) && searchString != String.Empty && searchHand == String.Empty)
    {
        books = books.Where(b => b.Name.ToUpper().Contains(searchString.ToUpper()));
    }
}

return View(books);

My view:

<p>Find by Name : @Html.TextBox("searchString", ViewBag.CurrentFilter as string)


@Html.DropDownList("searchGender", new SelectList(ViewBag.BookNames), "-- Select All --")
@Html.DropDownList("searchHand", new SelectList(ViewBag.HandNames), "---Select All--")

Answer 1

Just put if, not else if so you can have a cumulative multi criteria search, and one condition in every if.

So every condition is easy to read, and if more than one criteria is filled, they will cumulate fine.

if (!String.IsNullOrWhiteSpace(searchString))
   books = books.Where(b => b.Name.ToUpper().Contains(searchString.ToUpper());       

if (!String.IsNullOrWhiteSpace(searchGender))
   books = books.Where(b => b.Gender == searchGender);

if (String.IsNullOrWhiteSpace(searchHand))
   books = books.Where(b => b.Handedness == searchHand);

Answer 2

Ok, so I just recently arrived at a way of doing this sort of thing that I actually like so let me share.

In my opinion, the if statements aren't really the problem, its more that they are not really pertinent to controller code. Actions should strive to contain code only about major decisions of what code path will be executed.

Solution: You take advantage of the fact that a Linq query returns an IQueryable to store the query logic along with the model and an extension method to give it a nice DSL like interface. Similar to the pipes and filters pattern.

This is what the action is going to look like:

public ViewResult Index(SearchModel searchQuery) 
{
  var books = entities.Get<Book>()
                .Where(b=>b.IsInPrint)
                .FilterBy(searchQuery);
  return View(books);
}

And this is what my model looks like:

public class SearchModel 
{
   public string Text { get; set; }
   public bool InStockOnly { get; set; }
}
public static class SearchModelFilterQueryEx
{
  public static IQueryable<Book> FilterBy(this IQueryable<Book> query,  SearchModel search)
  {
    if(search == null)
      return query;
    if(!String.IsNullOrWhiteSpace(search.Text)) 
      query = query.Where(b=>b.Name.Contains(search.Text));
    if(String.InStockOnly)
      query = query.Where(b=>b.NumberInStock > 0);
    return query;
  }
}