Question

我想优化以下几行代码进行排序。

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));
        }

因为如果我有更多的10个字段来执行排序，这是非常繁琐的方式。

谢谢， Imdadhusen

Answer 1

我的实际目标有点模糊，但对于切换部分，您可以使用扩展方法，如下所示。

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));
    }
}

它将对排序顺序进行非常简化的解析。它将责任放在主叫方上，这通常不是你想要做的，因此如果排序顺序字符串不符合要求，你可能需要一些错误处理。

从sortorder字符串中获取一个名称，用于标识可用于获取用于排序的值的属性。

你可以像这样使用它：

db.TabMasters.SortByField(sortOrder)

根据评论编辑：

在没有任何错误处理的情况下，行类型（T）.GetProperty（字段）是脆弱的。它依赖于第一个标记作为类型T的公共属性的名称。如果名称与属性不匹配，它将返回null。包括它是否与Field名称匹配。获得FieldInfo的功能类似 prop.GetField（field）将返回一个fieldinfo对象，其中包含给定名称的公共字段，否则为null。要获取字段的值，只需省略GetValue调用的最后一个参数。

Answer 2

你应该看看Linq.DynamicQuery。此博文http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

中有更多信息

该库允许您编写以下代码：

var query = northwind.Products
                     .Where("CategoryID = 3 AND UnitPrice > 3")
                     .OrderBy("SupplierID");

而不是

var query = from p in northwind.Products
                where p.CategoryID == 3 && p.UnitPrice > 3
                orderby p.SupplierID
                select p;

如果要添加sortdirection：

var query = northwind.Products.OrderBy("SupplierID Descending");

如何优化排序代码？

2 个答案: