Linq：从DataTable中选择行

Question

我有一个包含3000条记录的DataTable。我想在Android SQLite & MS SQL之间进行复制。我想将数据集转换为JSON。我无法传递这么多的数据。所以我想第一次拿500条记录第二次500条记录。同样想做。所以我使用Linq从DataTable中选择记录。

public String ConverDataSetToJson(DataSet dsDownloadJson,int currentSplit) 
    { 
     StringBuilder Sb = new StringBuilder(); 
     int start = 0; 
     int end =500; 
     int chk = 0; 
     string json = ""; 
     int currentChk = currentSplit; 
     int total =0; 
     DataTable dt1 = new DataTable(); 

     if (dsDownloadJson.Tables.Count > 0) 
     { 
      Sb.Append("{"); 
      foreach (DataTable dt in dsDownloadJson.Tables) 
      { 
       DataTable dtDownloadJson = dt; 
       total = dtDownloadJson.Rows.Count; 
       // If row count less than 500, then take that amount 
       if (dtDownloadJson.Rows.Count < 500) 
       { 
        end = dtDownloadJson.Rows.Count; 
       } 

       //number of split data set 
       if (chk == 0) 
       { 
        if (dtDownloadJson.Rows.Count > 500) 
        { 
         if ((dtDownloadJson.Rows.Count/500) == 0) 
         { 
          chk = dtDownloadJson.Rows.Count/500; 
         } 
         else 
         { 
          chk = dtDownloadJson.Rows.Count/500 + 1; 
         } 
        } 
        else 
        { 
         chk = 1; 
        } 
        currentChk = 1; 
       } 
       else 
       { 
        currentChk = currentChk + 1; 
        start = currentChk * 500; 
        end = start + 500; 
        currentChk = chk; 
       } 

       var AllProducts = dtDownloadJson.AsEnumerable(); 
       if (AllProducts.Count() > 0) 
       { 
        var query1 = (from c in AllProducts select c).Skip(0); 

        query1 = (from c in query1 select c).Take((end - start) + 1); 
        int res = query1.Count(); 
        Console.WriteLine("---------" + res); 
        if (query1.Count() > 0) 
        { 
         dtDownloadJson.Rows.Clear(); 
         dt1 = query1.CopyToDataTable(); 
         int count = dt1.Rows.Count; 
         json = JsonConvert.SerializeObject(dt1, Formatting.Indented); 
        } 
       }      
      } 
     } 

     return json; 
    } 

请帮帮我，这给出了一个错误The Source contain no data source. When Go to CopyToDataTable行。

Answer 1

我相信你的错误实际上

是源不包含任何数据行。

由于@Pranay林蛙提到，查询并没有真正执行，直到调用CopyToDataTable，但那时的表是空的：如果删除调用Rows.Clear()

dtDownloadJson.Rows.Clear(); 
dt1 = query1.CopyToDataTable(); 

，您应该CopyToDataTable()跑。