C#如何将.OrderBy与多列一起使用并将列号解码为列名？

Question

所以我使用 Datatable.net、Asp.net MVC 控制器来提供 Json 数据。
我正在尝试做一些与这些帖子类似的事情：

• LINQ Sort by Multiple Fields
• Multi Column Sort for Datatables.net

从 Javascript Ajax 调用到服务器，我有以下参数：

> int iSortingCols    Number of columns to sort on
> int iSortCol_(int)  Column being sorted on 
>          (you will need to decode this number for your database)
> string  sSortDir_(int)  Direction to be sorted - "desc" or "asc".

这是我的数据集：

var db = new GER_MAPV_Context();
var allTags = db.TrimTables;
filteredTags = db.TrimTables.AsEnumerable();
IEnumerable<TrimTable> filteredTags;

//排序的依赖函数

Func<TrimTable, string> getColumnName = (
    c => getCurrentSortColumn(1) == 1 ? c.TAG :
    sortColumnIndex == 2 ? c.DESCRIPTION :
    sortColumnIndex == 3 ? c.SET_POINT :
    sortColumnIndex == 4 ? c.PRIORITY :
    sortColumnIndex == 5 ? c.LIMIT_TYPE :
    sortColumnIndex == 6 ? c.ALARM_TYPE :
    sortColumnIndex == 7 ? c.AUTOMATED_SYSTEM :
    sortColumnIndex == 8 ? c.COL_POL :
    sortColumnIndex == 9 ? c.PROPERTY :
    sortColumnIndex == 10 ? c.EQUIP_TYPE:
    sortColumnIndex == 11 ? c.P_ID :
    sortColumnIndex == 12 ? c.AREA :
    sortColumnIndex == 13 ? c.COMPLEX :
    sortColumnIndex == 14 ? c.UNIT :  //PI Unit Format Long-text
    sortColumnIndex == 15 ? c.UNIT_ : //Loop Number Format
    sortColumnIndex == 16 ? c.LOOP_TYPE : //Loop Type i.e. PI, FIT, PSV
    sortColumnIndex == 17 ? c.LOOP_ : //Loop Number
    sortColumnIndex == 18 ? c.LOOP_EXT  :
    c.UNIT
    );

然后我需要对这些列中的每一列进行相应的排序，最多 4 种。

filteredTags.OrderBy(getColumnName).ThenByDescending(getColumnName);
//could have 1 - 4 orderby.thenby arrangements

诀窍是我需要输入“sortColumnIndex”
（这是一个数字，分别是 iSortCol_1 或 iSortCol_2 的 JSON 参数）
进入 getColumnName 函数，使其返回正确的列名。

我在这里绞尽脑汁。

问：那么执行此操作的基本步骤是什么？
我在这里尝试构建的 LINQ 表达式的基本要点是什么？

Answer 1

我相信这对你有用。你只需要添加一个 lambda 函数。

var result = filteredTags
.OrderBy(t => getColumnName(t, iSortCol_1))
.ThenBy(t => getColumnName(t, iSortCol_2));

但是你的 getColumnName 需要有两个输入参数（table 和 columnNum）。

更新：

要包括排序列数和降序：

var r = firstDesc ? 
filteredTags
.OrderByDescending(t => getColumnName(iSortCol_1))
: filteredTags
.OrderBy(t => getColumnName(iSortCol_1))



for ( var i =1;  i < colCount; i++)
{
    r = nDesc ? 
    r.ThenByDescending(t => getColumnName(iSortCol_1))
    : r.OrderBy(t => getColumnName(iSortCol_1))
}

Answer 2

好的，如果有人好奇，这是我的最终代码： 我还发现这两个网站很有帮助：

• Multiple Field Sorting

• Farm Fresh Code MVC, DataTables

      //Dependent function for Sorting
      //This Functions Retrieves the Database Field Name to be used by the Orderby("Tag") function 
      // i.e. OrderBy(t => t.Area);
      // t = TrimTable
      // iSortCol = Column Number to Sort By
      Func<TrimTable, Int32, string> getColName =(
      (t, iSortCol) => iSortCol == 1 ? t.TAG :
                      iSortCol == 2 ? t.DESCRIPTION :
                      iSortCol == 3 ? t.SET_POINT :
                      iSortCol == 4 ? t.PRIORITY :
                      iSortCol == 5 ? t.LIMIT_TYPE :
                      iSortCol == 6 ? t.ALARM_TYPE :
                      iSortCol == 7 ? t.AUTOMATED_SYSTEM :
                      iSortCol == 8 ? t.COL_POL :
                      iSortCol == 9 ? t.PROPERTY :
                      iSortCol == 10 ? t.EQUIP_TYPE:
                      iSortCol == 11 ? t.P_ID :
                      iSortCol == 12 ? t.AREA :
                      iSortCol == 13 ? t.COMPLEX :
                      iSortCol == 14 ? t.UNIT :  //PI Unit Format Long-text
                      iSortCol == 15 ? t.UNIT_ : //Loop Number Format
                      iSortCol == 16 ? t.LOOP_TYPE : //Loop Type i.e. PI, FIT, PSV
                      iSortCol == 17 ? t.LOOP_ : //Loop Number
                      iSortCol == 18 ? t.LOOP_EXT  :
                      t.UNIT_
          );
  
  
     //Help Info: 
      //http://stackoverflow.com/questions/958220/how-can-i-use-linq-to-sort-by-multiple-fields
      //http://stackoverflow.com/questions/21582725/c-sharp-how-to-use-orderby-with-multiple-columns-and-decode-column-number-to-co#21583371
      //http://activeengine.net/2011/02/09/datatablepager-now-has-multi-column-sort-capability-for-datatables-net/
      //http://msdn.microsoft.com/en-us/library/bb534852(v=vs.110).aspx
  
  
      //Number of Columns to Sort
      int iSortCols = Convert.ToInt32(param.iSortingCols);
      Debug.WriteLine("Count of Sortable Columns" + iSortCols);
      //int   iSortCol_(int)  Column being sorted on (you will need to decode this number for your database)
      //string    sSortDir_(int)  Direction to be sorted - "desc" or "asc".
  
      //If Sort Expression Exists
      if (iSortCols > 0)
      {
          //Sorting
          string[] sSortDirection = new string[iSortCols]; // asc or desc
          Int32[] iSortColNum = new Int32[iSortCols]; //number
  
          //Get Sorting Parameters from MVC Controller
          for (int h = 0; h < iSortCols; h++)
          {
              //Get Sort Direction
              var s1 = "sSortDir_" + h;
              sSortDirection[h] = Convert.ToString(Request[s1]);
  
              //Get Sort Column Number
              var s2 = "iSortCol_" + h;
              iSortColNum[h] = Convert.ToInt32(Request[s2]);
  
          }
  
          //Build Orderby Statement
          for (int i = 0; i < iSortCols; i++)
          {
              // We need to keep the loop index, not sure why it is altered by the Linq.
              var index = i;
  
              //If Current Column is Ascending/Descending
              if (sSortDirection[index] == "asc")
              {
                  //Orderby / Thenby
                  orderedTags = (index == 0) ? filteredTags.OrderBy(t => getColName(t, iSortColNum[index]))
                                          : orderedTags.ThenBy(t => getColName(t, iSortColNum[index]));
  
              }
              else
              {
                  orderedTags = (index == 0) ? filteredTags.OrderByDescending(t => getColName(t, iSortColNum[index]))
                                         : orderedTags.ThenByDescending(t => getColName(t, iSortColNum[index]));
              }
  
          }
  
          //Return Orderby LINQ to Original Result Variable
          filteredTags = orderedTags;
      }
      else
      {
          //Default Sort if None is Selected
          filteredTags = filteredTags.OrderBy(t => t.TAG);
      }