如何動態添加降序到orderby？

Question

我可以排序依據語句動態地構建LINQ查詢象下面這樣：

var Query = from q in Db.TblUsers select q; 

switch (Order) 
{ 
    case "Name": Query = from q in Query orderby q.Name select q; break; 
    case "DOB": Query = from q in Query orderby q.DOB select q; break; 
    // ... and more cases 
} 

var Result = Query.ToList(); 

但是，如果有必要，責令降序（取決於用戶選擇在UI），我將不得不構造另一個switch語句複製所有的情況只是爲了在orderby之後添加「降序」關鍵字。

例如：

if (ascending) 
{ 
    switch (Order) 
    { 
     case "Name": Query = from q in Query orderby q.Name select q; break; 
     // .... 
    } 
} 
else 
{ 
    switch (Order) 
    { 
     case "Name": Query = from q in Query orderby q.Name descending select q; break; 
     // .... 
    } 
} 

有沒有辦法對我來說，動態地添加只是下降關鍵字查詢？

Answer 1

這不是很大，但它不是是不好：

var Query = Db.TblUsers.AsQueryable(); 

switch (Order) 
{ 
    case "Name": Query = ascending ? 
        Query.OrderBy(q=>q.Name) : 
        Query.OrderByDescending(q=>q.Name); 
     break; 
    case "DOB": Query = ascending ? 
        Query.OrderBy(q=>q.DOB) : 
        Query.OrderByDescending(q=>q.DOB); 
     break; 
    // ... and more cases 
} 

var Result = Query.ToList(); 

見

• OrderBy
• OrderByDescending

Answer 2

儘量考慮動態的LINQ我覺得它更容易爲你的解決方案重刑 http://weblogs.asp.net/scottgu/dynamic-linq-part-1-using-the-linq-dynamic-query-library

Answer 3

考慮：

public static class OrderByEx 
{ 
    public static IOrderedQueryable<TSource> OrderBy<TSource, TKey>(this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, bool ascending) 
    { 
     if (ascending) 
     { 
      return source.OrderBy(keySelector); 
     } 

     return source.OrderByDescending(keySelector); 
    } 
} 

您可以：

var Query = Db.TblUsers.AsQueryable(); 

switch (Order) 
{ 
    case "Name": 
     Query = Query.OrderBy(q=>q.Name, ascending); 
     break; 
    case "DOB": 
     Query = Query.OrderBy(q=>q.DOB, ascending); 
     break; 
    // ... and more cases 
}