How to optimize code for Sorting? - linq

Question

I would like to optimize following lines of code for Sorting.
public ViewResult Index(string sortorder, int? pagesize, int? page)
{
int pageSize = pagesize ?? 10;
if (Request.HttpMethod != "GET")
{
page = 1;
pageSize = 10;
}
ViewBag.SelectedPageSize = pageSize;
ViewBag.CurrentSort = sortorder;
ViewBag.FirstNameSortParm = String.IsNullOrEmpty(sortorder) ? "FirstName desc" : "";
ViewBag.LastNameSortParm = sortorder == "LastName" ? "LastName desc" : "LastName";
ViewBag.DepNameSortParm = sortorder == "depName" ? "depName desc" : "depName";
var joined = from tm in db.TabMasters select tm;
switch (sortorder)
{
case "FirstName":
joined = joined.OrderBy(m => m.FirstName);
break;
case "FirstName desc":
joined = joined.OrderByDescending(m => m.FirstName);
break;
case "LastName":
joined = joined.OrderBy(m => m.LastName);
break;
case "LastName desc":
joined = joined.OrderByDescending(m => m.LastName);
break;
case "depName":
joined = joined.OrderBy(m => m.depName);
break;
case "depName desc":
joined = joined.OrderByDescending(m => m.depName);
break;
default:
joined = joined.OrderBy(m => m.FirstName);
break;
}
int pageIndex = (page ?? 1) - 1;
int start = (pageIndex * pageSize);
ViewBag.TotalRecord = joined.Count();
ViewBag.StartRecord = start + 1;
ViewBag.EndRecord = ((start + pageSize) >= ViewBag.TotalRecord) ? ViewBag.TotalRecord : (start + pageSize);
return View(joined.ToPagedList(pageIndex, pageSize));
}
Because this is very tedious way if i have more the 10 fields to perform sort.
Thanks,
Imdadhusen

Answer 1

It's a bit vague to me what your actual goal is but for the switch part you could use an extension method as the below.
public static class SortExtensions
{
public static IEnumerable<T> SortByField<T>(this IEnumerable<T> sequence, string sortOrder)
{
var tokens = sortOrder.Trim().Split(' ');
var field = tokens[0];
var direction = tokens.Skip(1).Single().ToLower();
var prop = typeof(T).GetProperty(field);
return direction == "desc"
? sequence.OrderByDescending(m => prop.GetValue(m, null))
: sequence.OrderBy(m => prop.GetValue(m, null));
}
}
It will make a very simplified parsing of the sort order. It puts the responsibility on the calling party which is generally not what you want to do, so you might want some error handling in case the sortorder string does not fulfill the requirements.
from the sortorder string it fetches a name used to identify a property which can be used to fetch the value used for sorting.
you can use it like this:
db.TabMasters.SortByField(sortOrder)
EDIT based on comment:
The line typeof(T).GetProperty(field) is fragile in the absence of any error handling. It relies on the first token to be a name of a public property of the type T. It will return null if the name doesn't match a property. Including if it matches a Field name. A similar function exist for getting a FieldInfo
prop.GetField(field) will return a fieldinfo object of there's a public field with the given name otherwise null. To get the value of a field simply omit the last parameter to the GetValue call.

Answer 2

You should take a look at Linq.DynamicQuery.
There's more info in this blogpost http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx
The library lets you write following code:
var query = northwind.Products
.Where("CategoryID = 3 AND UnitPrice > 3")
.OrderBy("SupplierID");
instead of
var query = from p in northwind.Products
where p.CategoryID == 3 && p.UnitPrice > 3
orderby p.SupplierID
select p;
If you want to add the sortdirection:
var query = northwind.Products.OrderBy("SupplierID Descending");