我正在使用EF从db获取数据。当我提取然后我也过滤和排序数据。这样我按列名排序。我必须写出一条看起来不太好的巨行。
switch (SortColumn)
{
case "CompanyName":
ViewBag.OldSort = "CompanyName";
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(m => m.CompanyName);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(m => m.CompanyName);
ViewBag.SortOrder = "asc";
}
break;
case "ContactName":
ViewBag.OldSort = "ContactName";
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(m => m.ContactName);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(m => m.ContactName);
ViewBag.SortOrder = "asc";
}
break;
case "ContactTitle":
ViewBag.OldSort = "ContactTitle";
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(m => m.ContactTitle);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(m => m.ContactTitle);
ViewBag.SortOrder = "asc";
}
break;
case "Address":
ViewBag.OldSort = "Address";
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(m => m.Address);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(m => m.Address);
ViewBag.SortOrder = "asc";
}
break;
case "Default":
ViewBag.OldSort = "CompanyName";
customer = customer.OrderBy(m => m.CompanyName);
ViewBag.SortOrder = "asc";
break;
}
请参阅4列我必须编写这么多行代码。假设我需要使用40列，那么我需要写多少行。所以告诉我在使用EF时最小化排序代码的最佳选择。
看看我的完整工作代码，其中给出了完整的代码，以了解我使用过滤器对数据进行排序和获取的方法。现在告诉我如何最小化排序代码，使用提取数据进行过滤。
private CustomersEntities db = new CustomersEntities();
public int recordcount = 0;
// GET: Customers
public ActionResult Index(int? page, string SortColumn, string CurrentSort, String SearchText)
{
var customer = (from s in db.Customers
// select s;
select new CustomerDTO
{
CustomerID = s.CustomerID,
CompanyName = s.CompanyName,
ContactName = s.ContactName,
ContactTitle = s.ContactTitle,
Address = s.Address
});
int pageSize = 5;
int pageNumber = (page ?? 1);
ViewBag.CurrentPage = pageNumber;
SortColumn = String.IsNullOrEmpty(SortColumn) ? "CompanyName" : SortColumn;
ViewBag.CurrentSort = SortColumn;
//ViewBag.OldSort = CurrentSort;
ViewBag.SearchText = SearchText;
if (!String.IsNullOrEmpty(SearchText))
{
customer = customer.Where(s => s.CompanyName.ToUpper().Contains(SearchText.ToUpper())
|| s.ContactName.ToUpper().Contains(SearchText.ToUpper())
|| s.ContactTitle.ToUpper().Contains(SearchText.ToUpper())
|| s.Address.ToUpper().Contains(SearchText.ToUpper()));
}
switch (SortColumn)
{
case "CompanyName":
ViewBag.OldSort = "CompanyName";
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(m => m.CompanyName);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(m => m.CompanyName);
ViewBag.SortOrder = "asc";
}
break;
case "ContactName":
ViewBag.OldSort = "ContactName";
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(m => m.ContactName);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(m => m.ContactName);
ViewBag.SortOrder = "asc";
}
break;
case "ContactTitle":
ViewBag.OldSort = "ContactTitle";
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(m => m.ContactTitle);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(m => m.ContactTitle);
ViewBag.SortOrder = "asc";
}
break;
case "Address":
ViewBag.OldSort = "Address";
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(m => m.Address);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(m => m.Address);
ViewBag.SortOrder = "asc";
}
break;
case "Default":
ViewBag.OldSort = "CompanyName";
customer = customer.OrderBy(m => m.CompanyName);
ViewBag.SortOrder = "asc";
break;
}
IPagedList<CustomerDTO> oCustomer = customer.ToPagedList(pageNumber, pageSize);
return View(oCustomer);
}
ViewBag.OldSort = SortColumn;
var arg = Expression.Parameter(typeof(Customer), "x");
var exprProp = Expression.Property(arg, SortColumn);
var projection = Expression.Lambda<Func<Customer, string>>(exprProp, arg);
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(projection);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(projection);
ViewBag.SortOrder = "asc";
}
假设您的所有可排序列都是字符串：
private static readonly IReadOnlyDictionary<string, Expression<Func<Customer, string>>> SortColumns = new Dictionary<string, Expression<Func<Customer, string>>>
{
["CompanyName"] = c => c.CompanyName,
["ContactName"] = c => c.ContactName,
["ContactTitle"] = c => c.ContactTitle,
["Address"] = c => c.Address,
};
...
if (SortColumns.TryGetValue(SortColumn, out var sortProperty))
{
ViewBag.OldSort = SortColumn;
if (SortColumn.Equals(CurrentSort))
{
customer = customer.OrderByDescending(sortProperty);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = customer.OrderBy(sortProperty);
ViewBag.SortOrder = "asc";
}
}
else
{
customer = customer.OrderBy(c => c.CompanyName);
ViewBag.OldSort = "CompanyName";
ViewBag.SortOrder = "asc";
}
这稍微复杂一些。
首先添加必要的using指令：
using System.Linq;
using System.Linq.Expressions;
接下来，您需要一个基于LambdaExpression进行排序的方法：
private static IOrderedQueryable<TSource> OrderBy<TSource>(IQueryable<TSource> source, LambdaExpression keySelector, bool descending)
{
string methodName = descending ? "OrderByDescending" : "OrderBy";
Type[] typeArguments = { typeof(TSource), keySelector.ReturnType };
var query = Expression.Call(typeof(Queryable), methodName, typeArguments, source.Expression, keySelector);
return (IOrderedQueryable<TSource>)source.Provider.CreateQuery<TSource>(query);
}
然后，您需要更新字典以存储LambdaExpression值。要干净利落地完成这项工作，您需要一个帮助方法将匿名委托转换为LambdaExpression：
private static LambdaExpression Expr<TProperty>(Expression<Func<Customer, TProperty>> fn) => fn;
private static readonly IReadOnlyDictionary<string, LambdaExpression> SortColumns = new Dictionary<string, LambdaExpression>
{
["CompanyName"] = Expr(c => c.CompanyName),
["ContactName"] = Expr(c => c.ContactName),
["ContactTitle"] = Expr(c => c.ContactTitle),
["Address"] = Expr(c => c.Address),
};
最后，更新您的排序代码以使用新方法：
if (SortColumns.TryGetValue(SortColumn, out var keySelector))
{
ViewBag.OldSort = SortColumn;
if (SortColumn.Equals(CurrentSort))
{
customer = OrderBy(customer, keySelector, true);
ViewBag.CurrentSort = "";
ViewBag.SortOrder = "desc";
}
else
{
customer = OrderBy(customer, keySelector, false);
ViewBag.SortOrder = "asc";
}
}
else
{
customer = customer.OrderBy(c => c.CompanyName);
ViewBag.OldSort = "CompanyName";
ViewBag.SortOrder = "asc";
}
现在我们可以按任何属性类型排序。