在c#中向Datatable添加行

本文关键字：添加行 Datatable 中向 | 更新日期: 2023-09-27 18:09:33

我正在一个项目上工作，我想添加行到数据表和正在发生的事情是，如果我从数据库中获取两行，只有其中一个被添加到数据表中，但我希望两者都被添加到数据表中，即数据表不能保存第一行的数据，数据正在被第二行数据覆盖。该方法的代码为。这是我的通话记录。

    DataTable dttable = new DataTable();
    dttable = gettable(dtgreater, dtcurrentdate);
    public DataTable gettable(List<DateTime> objct1, DateTime objct2)
    {
    DataTable data=null;
    for (int j = 0; j < dtgreater.Count; j++)
    {
        sql = "select library_issue.STUDENTCODE,library_issue.studentname,library_book.bookname,library_issue.issuedate,library_issue.returndate from library_issue             join library_book on library_book.book_id = library_issue.book_id where library_issue.returndate ='" + objct1[j].ToString("dd/MM/yyyy") + "'";
        ds = obj.openDataset(sql, Session["SCHOOLCODE"].ToString());
        Label1.Text = (ds.Tables[0].Rows.Count).ToString();
        data = new DataTable();
        data.Columns.Add("STUDENTCODE", typeof(int));
        data.Columns.Add("Studentname", typeof(string));
        data.Columns.Add("Bookname", typeof(string));
        data.Columns.Add("Issuedate", typeof(string));
        data.Columns.Add("Returndate", typeof(string));
        data.Columns.Add("NO of Days Exceeded", typeof(string));
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            TimeSpan ts = objct1[j] - objct2;
            Label1.Text = ts.ToString("dd");
            data.Rows.Add(ds.Tables[0].Rows[i]["STUDENTCODE"], ds.Tables[0].Rows[i]["studentname"], ds.Tables[0].Rows[i]["bookname"], ds.Tables[0].Rows[i]["issuedate"], ds.Tables[0].Rows[i]["returndate"], ts.ToString("dd"));
        }
    }
     return data;
}

更新:

   public DataTable gettable(List<DateTime> objct1, DateTime objct2)
    {
        DataTable data = new DataTable();
        data.Columns.Add("STUDENTCODE", typeof(int));
        data.Columns.Add("Studentname", typeof(string));
        data.Columns.Add("Bookname", typeof(string));
        data.Columns.Add("Issuedate", typeof(string));
        data.Columns.Add("Returndate", typeof(string));
        data.Columns.Add("NO of Days Exceeded", typeof(string));
    for (int j = 0; j < dtgreater.Count; j++)
    {
        sql = "select library_issue.STUDENTCODE,library_issue.studentname,library_book.bookname,library_issue.issuedate,library_issue.returndate from library_issue             join library_book on library_book.book_id = library_issue.book_id where library_issue.returndate ='" + objct1[j].ToString("dd/MM/yyyy") + "'";
        ds = obj.openDataset(sql, Session["SCHOOLCODE"].ToString());
        Label1.Text = (ds.Tables[0].Rows.Count).ToString();
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            TimeSpan ts = objct1[j] - objct2;
            Label1.Text = ts.ToString("dd");
            data.Rows.Add(ds.Tables[0].Rows[i]["STUDENTCODE"], ds.Tables[0].Rows[i]["studentname"], ds.Tables[0].Rows[i]["bookname"], ds.Tables[0].Rows[i]["issuedate"], ds.Tables[0].Rows[i]["returndate"], ts.ToString("dd"));
        }
    }
     return data;
}

description:当我在for循环中初始化数据表时，每次都会导致创建新的数据表实例。作为结果，我每次只得到一行。

在c#中向Datatable添加行

您在循环中创建数据表，因此在第二次迭代中，它将丢弃包含第一个项目的第一个数据表，并为第二个项目创建一个新的空数据表。

创建数据表，并在循环前添加列:

DataTable dttable = new DataTable();
dttable = gettable(dtgreater, dtcurrentdate);
public DataTable gettable(List<DateTime> objct1, DateTime objct2)
{
  DataTable data = new DataTable();
  data.Columns.Add("STUDENTCODE", typeof(int));
  data.Columns.Add("Studentname", typeof(string));
  data.Columns.Add("Bookname", typeof(string));
  data.Columns.Add("Issuedate", typeof(string));
  data.Columns.Add("Returndate", typeof(string));
  data.Columns.Add("NO of Days Exceeded", typeof(string));
  for (int j = 0; j < dtgreater.Count; j++) {
    sql = "select library_issue.STUDENTCODE,library_issue.studentname,library_book.bookname,library_issue.issuedate,library_issue.returndate from library_issue             join library_book on library_book.book_id = library_issue.book_id where library_issue.returndate ='" + objct1[j].ToString("dd/MM/yyyy") + "'";
    ds = obj.openDataset(sql, Session["SCHOOLCODE"].ToString());
    Label1.Text = (ds.Tables[0].Rows.Count).ToString();
    for (int i = 0; i < ds.Tables[0].Rows.Count; i++) {
        TimeSpan ts = objct1[j] - objct2;
        Label1.Text = ts.ToString("dd");
        data.Rows.Add(ds.Tables[0].Rows[i]["STUDENTCODE"], ds.Tables[0].Rows[i]["studentname"], ds.Tables[0].Rows[i]["bookname"], ds.Tables[0].Rows[i]["issuedate"], ds.Tables[0].Rows[i]["returndate"], ts.ToString("dd"));
    }
  }
  return data;
}

将表创建置于循环之外。

DataTable data = new DataTable();

最好使用这样的foreach:

例如:

foreach (var dr in ds.Tables.First().Rows)
{
   string studentCode = dr["STUDENTCODE"].ToString();
}

删除行:data = new DataTable();

在For循环外创建Datatable，如下所示…

    DataTable data = new DataTable();
    data.Columns.Add("STUDENTCODE", typeof(int));
    data.Columns.Add("Studentname", typeof(string));
    data.Columns.Add("Bookname", typeof(string));
    data.Columns.Add("Issuedate", typeof(string));
    data.Columns.Add("Returndate", typeof(string));
    data.Columns.Add("NO of Days Exceeded", typeof(string))
    for (int j = 0; j < dtgreater.Count; j++)
     {

你可以做的是

    DataTable dttable = new DataTable();
    dttable = gettable(dtgreater, dtcurrentdate);
    public DataTable gettable(List<DateTime> objct1, DateTime objct2)
    {
    DataTable data=null;
    for (int j = 0; j < dtgreater.Count; j++)
    {
        sql = "select library_issue.STUDENTCODE,library_issue.studentname,library_book.bookname,library_issue.issuedate,library_issue.returndate from library_issue             join library_book on library_book.book_id = library_issue.book_id where library_issue.returndate ='" + objct1[j].ToString("dd/MM/yyyy") + "'";
        ds = obj.openDataset(sql, Session["SCHOOLCODE"].ToString());
        Label1.Text = (ds.Tables[0].Rows.Count).ToString();
       if(data.Columns.count==0)
        {
        data = new DataTable();
        data.Columns.Add("STUDENTCODE", typeof(int));
        data.Columns.Add("Studentname", typeof(string));
        data.Columns.Add("Bookname", typeof(string));
        data.Columns.Add("Issuedate", typeof(string));
        data.Columns.Add("Returndate", typeof(string));
        data.Columns.Add("NO of Days Exceeded", typeof(string));
        }
        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
        {
            TimeSpan ts = objct1[j] - objct2;
            Label1.Text = ts.ToString("dd");
            data.Rows.Add(ds.Tables[0].Rows[i]["STUDENTCODE"], ds.Tables[0].Rows[i]["studentname"], ds.Tables[0].Rows[i]["bookname"], ds.Tables[0].Rows[i]["issuedate"], ds.Tables[0].Rows[i]["returndate"], ts.ToString("dd"));
        }
    }
     return data;
}

我想这对你会有用

DataTable dttable = new DataTable();
dttable = gettable(dtgreater, dtcurrentdate);
public DataTable gettable(List<DateTime> objct1, DateTime objct2)
{
    DataTable data=null;
    sql = "select library_issue.STUDENTCODE,library_issue.studentname,library_book.bookname,library_issue.issuedate,library_issue.returndate from library_issue             join library_book on library_book.book_id = library_issue.book_id where library_issue.returndate ='" + objct1[j].ToString("dd/MM/yyyy") + "'";
    ds = obj.openDataset(sql, Session["SCHOOLCODE"].ToString());
    Label1.Text = (ds.Tables[0].Rows.Count).ToString();

for (int j = 0; j < dtgreater.Count; j++)
{
   if(data.Columns.count==0)
    {
    data = new DataTable();
    data.Columns.Add("STUDENTCODE", typeof(int));
    data.Columns.Add("Studentname", typeof(string));
    data.Columns.Add("Bookname", typeof(string));
    data.Columns.Add("Issuedate", typeof(string));
    data.Columns.Add("Returndate", typeof(string));
    data.Columns.Add("NO of Days Exceeded", typeof(string));
    }
    for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
    {
        TimeSpan ts = objct1[j] - objct2;
        Label1.Text = ts.ToString("dd");
        data.Rows.Add(ds.Tables[0].Rows[i]["STUDENTCODE"], ds.Tables[0].Rows[i]["studentname"], ds.Tables[0].Rows[i]["bookname"], ds.Tables[0].Rows[i]["issuedate"], ds.Tables[0].Rows[i]["returndate"], ts.ToString("dd"));
}
 return data;
}

Var.GRV.Columns.Add("NAME COLUMN");
            Var.GRV.Columns.Add("NAME COLUMN");
            Var.GRV.Columns.Add("*");
            Var.GRV.Columns.Add("*");
            Var.GRV.Columns.Add("*");
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