如何在ASP.NET C＃中动态更改数据列的数据类型？ [英] How to change datatype of datacolumn dynamically in ASP.NET C#?

问题描述

我正在动态创建数据表。我正在从DB添加数据类型和列名称。但是在创建数据表时动态地从DB获取Int32 / double数据类型时，我遇到问题一旦列有数据就无法更改列的数据类型



我尝试过：

 StreamReader Rep001Stream =  new  StreamReader（filePath）; 
 尝试 
 {
  if （dsStdRep001SchemaDetails.Tables [ 0 ]。Rows.Count >   0 ） 
 {
  string  [] words; 
 DataRow row =  null ; 
 尝试 
 {
  string  Rep001Record =  ; 
  while （！Rep001Stream.EndOfStream）
 {
 Rep001Record = Rep001Stream.ReadLine（）; 
  for （ int  i =  0 ; i <  dsStdRep001SchemaDetails.Tables [ 0 ]。Rows.Count; i ++）
 {
  int  temp = i; 
 System.Data.DataTable dtTemp1 =  new  System.Data.DataTable（）; 
 dtTemp1.Columns.Add（ new  DataColumn（ 列 + i））; 
 dtRep001.Columns [i] .DataType = System.Type.GetType（  System。 + dsStdRep001SchemaDetails.Tables [ 0 ]。行[i] [  ColumnType]的ToString（））; 
 dtRep001.Columns [i] .ColumnName = dsStdRep001SchemaDetails.Tables [ 0 ]。行[i] [   ColumnName]。ToString（）; 
  string  ColumnId = dtRep001.Columns [i] .ColumnName.ToString（）; 
 words = Rep001Record.Split（' ，'）; 
  if （字[ 0 ]！= STR_RPT_END）
 {
  if （i ==  0 ）
 {
 row = dtRep001.NewRow （）; 
 dtRep001.Rows.Add（row）; 
} 
  //   row [ColumnId] = words [i] .Trim（）;  
} 
} 
} 
} 
  catch （例外情况）
 {
} 
} 
 Rep001Stream.Close（）; 
 Rep001Stream.Dispose（）; 
} 
  catch （例外情况）
 {
 objFileDetails.Status =   E; 
 objFileDetails.ErrorDescription = ex.Message; 
  bool  Succeeded = SaveFile（objFileDetails）; 
 Common.WriteLogService（ 错误： + ex.Message，ex.StackTrace，< span class =code-keyword> true ）; 
 Rep001Stream.Close（）; 
 Rep001Stream.Dispose（）; 
} 

解决方案

这是如何使用C＃动态更改数据类型到ASP.NET中的动态数据表？ [ ^ ]



无论如何，

首先尝试将所有数据CAST到单个数据类型从数据库中提取。 
 
示例：< pre>从表中选择强制转换（columnName as int）columnName 

参考：< a href =http://stackoverflow.com/questions/9028029/how-to-change-datatype-of-a-datacolumn-in-a-datatable> c＃ - 如何更改DataTable中DataColumn的DataType？ - 堆栈溢出 [ datatype-of-a-datacolumn-in-a-datatabletarget =_ blanktitle =新窗口> ^ ]

在此自定义数据类型

 Temp1.Columns.Add（new DataColumn（Column+ i））; 

喜欢这个

 Temp1.Columns.Add（new DataColumn（Column+ i），typeof（int））; 

I am creating a datatable dynamically. I am adding the datatype and column name from DB. but I am getting issue "cannot change datatype of column once a column has data" on fetching Int32 /double datatype from DB while creating a data table dynamically

What I have tried:

StreamReader Rep001Stream = new StreamReader(filePath);
try
{
  if (dsStdRep001SchemaDetails.Tables[0].Rows.Count > 0)
  {
    string[] words;
    DataRow row=null;
    try
    {
      string Rep001Record = "";
      while (!Rep001Stream.EndOfStream)
      {
        Rep001Record = Rep001Stream.ReadLine();
        for (int i = 0; i < dsStdRep001SchemaDetails.Tables[0].Rows.Count; i++)
        {
          int temp = i;
          System.Data.DataTable dtTemp1 = new System.Data.DataTable();
          dtTemp1.Columns.Add(new DataColumn("Column" + i));
          dtRep001.Columns[i].DataType = System.Type.GetType("System." + dsStdRep001SchemaDetails.Tables[0].Rows[i]["ColumnType"].ToString());
          dtRep001.Columns[i].ColumnName = dsStdRep001SchemaDetails.Tables[0].Rows[i]["ColumnName"].ToString();
          string ColumnId = dtRep001.Columns[i].ColumnName.ToString();
          words = Rep001Record.Split(',');
          if (words[0] != STR_RPT_END)
          {
            if (i == 0)
            {
              row = dtRep001.NewRow();
              dtRep001.Rows.Add(row);
            }
            // row[ColumnId] = words[i].Trim();
          }
        }
      }
    }
    catch (Exception ex)
    {
    }
  }
  Rep001Stream.Close();
  Rep001Stream.Dispose();
}
catch (Exception ex)
{
  objFileDetails.Status = "E";
  objFileDetails.ErrorDescription = ex.Message;
  bool Succeeded = SaveFile(objFileDetails);
  Common.WriteLogService("Error : " + ex.Message, ex.StackTrace, true);
  Rep001Stream.Close();
  Rep001Stream.Dispose();
}

解决方案

This is a duplicate of How to change datatype dynamically to a dynamic data table in ASP.NET with C#?[^]

Anyway,

Try CAST all your data to a single datatype first when extracting from database.

Example: <pre>select cast(columnName as int) columnName from table

Reference: c# - How To Change DataType of a DataColumn in a DataTable? - Stack Overflow[^]

Define datatype here itself

Temp1.Columns.Add(new DataColumn("Column" + i));

like this

Temp1.Columns.Add(new DataColumn("Column" + i), typeof(int));

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