c# - How to change DataTable columns order

Change the order of the columns in a DataTable
The DataTable class represents one table of in-memory data. The DataTable objects are conditionally case-sensitive. To create a DataTable programmatically the asp.net developers must first define its schema by adding DataColumn objects to the DataColumnCollection. To add rows to a DataTable, the developers must first use the NewRow() method to return a new DataRow object. The DataTable also contains a collection of Constraint objects that can be used to ensure the integrity of the data.

The following asp.net c# tutorial code demonstrates how we can change the order of the columns within a DataTable. So we have to change a specified DataColumn object’s order/position in a DataTable instance.

Here we used the DataTable class Columns property to get its columns collection as a DataColumnCollection object. Then we used DataColumnCollection’s Item[Int32] property to get the specified DataColumn instance.

After getting the DataColumn by index we can change this column’s order within the DataTable instance. The DataColumn class SetOrdinal(Int32) method changes the ordinal or position of the DataColumn to the specified ordinal or position.

The DataColumn class SetOrdinal(int ordinal) has a parameter named ordinal. The ordinal parameter is an Int32 which specified the column’s ordinal.

The DataColumn class SetOrdinal() method throws ArgumentException when the asp.net developers set the ordinal to less than 0 or greater than the ordinal of the last column.

When the asp.net c# developers change a column's ordinal, the DataColumn is moved to the new position in the collection of columns. Any columns between the previous and new ordinal will be renumbered, to adjust for a column's new ordinal.
DataColumnSetOrdinal.aspx

<%@ Page Language="C#" AutoEventWireup="true" %>
<%@ Import Namespace="System.Data" %>

<!DOCTYPE html>
<script runat="server">
    void Button1_Click(object sender, System.EventArgs e)
    {
        DataTable dt = new DataTable();
        dt.TableName = "Books";

        DataColumn dc1 = new DataColumn();
        dc1.ColumnName = "BookID";
        dc1.DataType = typeof(int);
        dc1.AllowDBNull = false;

        DataColumn dc2 = new DataColumn();
        dc2.ColumnName = "BookName";
        dc2.DataType = typeof(string);

        DataColumn dc3 = new DataColumn();
        dc3.ColumnName = "Author";
        dc3.DataType = typeof(string);
        
        dt.Columns.AddRange(new DataColumn[] { dc1,dc2,dc3 });

        dt.Rows.Add(new object[] { 1, "Learning Flash CS4 Professional", "Rich Shupe" });
        dt.Rows.Add(new object[] { 2, "Search Engine Optimization for Flash", "Todd Perkins" });
        dt.Rows.Add(new object[] { 3, "Dreamweaver CS4: The Missing Manual", "David Sawyer McFarland" });
        
        GridView1.DataSource = dt;
        GridView1.DataBind();

        Label1.Text = "<b><u>Columns with Ordinal....</u></b><br />";
        for (int i=0; i< dt.Columns.Count; i++)
        {
            Label1.Text += dt.Columns[i].ColumnName + " || ";
            Label1.Text += dt.Columns[i].Ordinal + "<br/ >";
        }

        dt.Columns[1].SetOrdinal(2);
        Label1.Text += "after Ordinal change......";
        GridView2.DataSource = dt;
        GridView2.DataBind();
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>Using SetOrdinal() method - How to set change DataColumn Ordinal in DataTable in ado.net</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:DarkBlue; font-style:italic;">
            Using SetOrdinal() method - How to set
            <br /> change DataColumn Ordinal in DataTable in ado.net
        </h2>
        <hr width="525" align="left" color="CornFlowerBlue" />
        <asp:GridView 
            ID="GridView1"
            runat="server"
            BorderColor="Snow"
            ForeColor="Snow"
            Width="550"
            >
            <HeaderStyle BackColor="DarkBlue" Height="35" />
            <RowStyle BackColor="DodgerBlue" />
            <AlternatingRowStyle BackColor="SkyBlue" />
        </asp:GridView>
        <asp:Label
             ID="Label1"
             runat="server"
             Font-Size="Medium"
             ForeColor="HotPink"
             >
        </asp:Label>
        <asp:GridView 
            ID="GridView2"
            runat="server"
            BorderColor="Snow"
            ForeColor="Snow"
            Width="550"
            >
            <HeaderStyle BackColor="DarkBlue" Height="35" />
            <RowStyle BackColor="DodgerBlue" />
            <AlternatingRowStyle BackColor="SkyBlue" />
        </asp:GridView>
        <asp:Button 
            ID="Button1"
            runat="server"
            OnClick="Button1_Click"
            Text="Populate GridView"
            Height="45"
            Font-Bold="true"
            ForeColor="DarkBlue"
            />
    </div>
    </form>
</body>
</html>
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