c# Linq操作DataTable

最新推荐文章于 2025-02-12 17:57:06 发布

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最新推荐文章于 2025-02-12 17:57:06 发布

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分类专栏： c#+linq 文章标签： linq C# datatable linq datatable wpf+datagrid

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本文介绍如何使用LINQ查询处理DataTable中的数据，包括筛选特定位置的记录并进行排序等操作。同时探讨了不同数据绑定方法对结果的影响。

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在平时的工作中，可能有很多情况下要对DataTable的里面的数据进行处理，最简单的例子如：对DataTable中的某个字段进行排序，根据条件筛选DataTable中的数据。。。，例子很多，下面我们看看如何处理的：

这是我最初写的代码：

代码

public static IEnumerable getEnumerable()
{
  DataTable dt = getDatatable();
   try
  {
   var query = from q in dt.AsEnumerable()
    where q.Field < string > ( " IPLocation " ) == " 北京 "
   select new
   {
   IPid = q.Field < int > ( " IPid " ),
   IPFrom = q.Field < string > ( " IPFrom " ),
   IPTo = q.Field < string > ( " IPTo " ),
   IPCity = q.Field < string > ( " IPCity " ),
   IPToNumber = q.Field < string > ( " IPToNumber " ),
   IPFromNumber = q.Field < string > ( " IPFromNumber " )
   };
    return query;
   }
    catch
   {
       return null ;
            }
}

然后我在最后做数据源绑定的时候，总是报System.InvalidCastException: 指定的转换无效的错误，无论用Gridview的自动生成列，还是Reapter的手动添加列，都有问题，最后我查出生成的结果集就含有异常的存在，也就说再取结果集的时候，要慎重用如下写法：

IPid = q.Field<int>("IPid"),

IPFrom = q.Field<string>("IPFrom"),

IPTo = q.Field<string>("IPTo"),

IPCity = q.Field<string>("IPCity"),

IPToNumber = q.Field<string>("IPToNumber"),

IPFromNumber = q.Field<string>("IPFromNumber")

我后来尝试了另一种写法：

IPid = q["IPid"].ToString(),

IPFrom = q["IPFrom"].ToString(),

IPTo = q["IPTo"].ToString(),

IPLocation = q["IPLocation"].ToString(),

IPCity = q["IPCity"].ToString(),

IPToNumber = q["IPToNumber"].ToString(),

IPFromNumber = q["IPFromNumber"].ToString()

一开始我调试也还是报System.InvalidCastException: 指定的转换无效这个错误，我调试了一段时间，也还是有问题，我在想是不是数据绑定控件的问题，后来我将原来的Gridview自动生成列换成了手动输入列：

代码

< table  align = " center " width = " 100% " cellpadding = " 0 " cellspacing = " 0 " style = " border: Gray 1px solid; margin-top:5px; margin-bottom:10px " >
         < asp:Repeater ID = " rpTest " runat = " server " >
         < HeaderTemplate >
           < tr >
              < th style = " background-color:Gray; color:White;border: Gray 1px solid;text-align:center " > ID </ th >
              < th style = " background-color:Black; color:White;border: Gray 1px solid;text-align:center " > IPFrom </ th >
              < th style = " background-color:Black; color:White;border: Gray 1px solid;text-align:center " > IPTo </ th >
              < th style = " background-color:Black; color:White;border: Gray 1px solid;text-align:center " > IPLocation </ th >
              < th style = " background-color:Black; color:White;border: Gray 1px solid;text-align:center " > City </ th >
              < th style = " background-color:Black; color:White;border: Gray 1px solid;text-align:center " > IPToNumber </ th >
              < th style = " background-color:Black; color:White;border: Gray 1px solid;text-align:center " > IPFromNumber </ th >
           </ tr >
         </ HeaderTemplate >
            < ItemTemplate >
               < tr >
                 < td style = " border: Gray 1px solid;text-align:center; " ><% #Eval( " IPid " ) %></ td >
                 < td style = " border: Gray 1px solid;text-align:center; " ><% #Eval( " IPFrom " ) %></ td >
                 < td style = " border: Gray 1px solid;text-align:center; " ><% #Eval( " IPTo " ) %></ td >
                 < td style = " border: Gray 1px solid;text-align:center; " ><% #Eval( " IPLocation " ) %></ td >
                 < td style = " border: Gray 1px solid;text-align:center; " >
                    <% #Eval( " IPCity " ) %>
                 </ td >
                 < td style = " border: Gray 1px solid;text-align:center; " ><% #Eval( " IPToNumber " ) %></ td >
                 < td style = " border: Gray 1px solid;text-align:center; " ><% #Eval( " IPFromNumber " ) %></ td >

              </ tr >
            </ ItemTemplate >
         </ asp:Repeater >
       </ table >

后来问题就解决了，我现在也不知道这个问题什么原因，为什么不支持自动产生列呢（等待高手帮忙解决）？

知道问题的所在了，然后就可以随心的处理DataTable里面的数据了，如下面一个简单的小例子：

代码

public static IEnumerable getEnumerable()
        {
            DataTable dt = getDatatable();
             try
            {
                var query = from q in dt.AsEnumerable()
                            orderby long .Parse(q[ " IPid " ].ToString()) descending
                             where q[ " IPid " ].ToString() == " 345058 "
                            select new
                            {
                                IPid = q[ " IPid " ].ToString(),
                                IPFrom = q[ " IPFrom " ].ToString(),
                                IPTo = q[ " IPTo " ].ToString(),
                                IPLocation = q[ " IPLocation " ].ToString(),
                                IPCity = q[ " IPCity " ].ToString(),
                                IPToNumber = q[ " IPToNumber " ].ToString(),
                                IPFromNumber = q[ " IPFromNumber " ].ToString()
                            };
                 return query;
                 // List<IPInfo> list = new List<IPInfo>();
                 // foreach (var q in query)
                 // {
                 //     IPInfo model = new IPInfo();
                 //     model.IPCity = q.IPCity;
                 //     model.IPFrom = q.IPFrom;
                 //     model.IPFromNumber = q.IPFromNumber;
                 //     model.IPid = long.Parse(q.IPid);
                 //     model.IPLocation = q.IPLocation;
                 //     model.IPTo = q.IPTo;
                 //     model.IPToNumber = q.IPToNumber;
                 //     list.Add(model);
                 // }
                 // return list;
            }
             catch
            {
                 return null ;
            }
        }

当然更复杂的对DataTable的操作这里就不在敖述了，在这里我只是说明一下困扰我的问题。