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c# - How to merge two DataTables

DataTable Merge() Method
.NET framework's DataTable represents one table of in-memory data. DataTable is a central object in the ado.net library. DataSet and DataView both objects use DataTable.

The DataTable Merge() method allows us to merge the specified DataTable with the current DataTable. The Merge() method is used to merge two DataTable objects that have largely similar schemas. Child tables are not affected or merged with the current table. If a table has child tables as part of the relationship, each child table must be merged individually.

DataTable Merge method is overloaded, those are Merge(DataTable), Merge(DataTable, Boolean), and Merge(DataTable, Boolean, MissingSchemaAction).

DataTable Merge(DataTable) overloaded method allows us to merge the specified DataTable with the current DataTable. Merge(DataTable) requires passing a parameter named table. This table parameter value type is System.Data.DataTable which represents the DataTable to be merged with the current DataTable. This method allows a client application to have a refreshed DataTable with the latest data from the data source.

DataTable Merge(DataTable, Boolean) overloaded method allows us to merge the specified DataTable with the current DataTable, including whether to preserve changes in the current DataTable.

Merge(DataTable, Boolean) method requires passing two parameters named 'table' and 'preserveChanges'. this 'preserveChanges' parameter value data type is a Boolean. If we set this parameter value to true, it preserves changes in the current DataTable. The false value does not preserve changes. The preserveChanges parameter value true means, incoming values do not overwrite existing values in the current row version of the existing row.

DataTable Merge(DataTable, Boolean, MissingSchemaAction) overloaded method allows us to merge the specified DataTable with the current DataTable, including whether to preserve changes and how to handle missing schema in the current DataTable.

Merge(DataTable, Boolean, MissingSchemaAction) method has three required parameters named table, preserveChanges, and missingSchemaAction. This missingSchemaAction parameter value type is System.Data.MissingSchemaAction which represents one of the MissiingScemaAction values. MissingSchemaAction enumeration values are Add, AddWithKey, Error, and Ignore.

The following ADO.NET C# example code demonstrates to us how can we merge a specified DataTable with the current DataTable programmatically at run time in an ASP.NET application.
DataTableMergeMethod.aspx

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

<!DOCTYPE html>
<script runat="server">
    protected 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;
        dc1.Unique = 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, "Drupal 6 Social Networking", "Michael Peacock" });
        dt.Rows.Add(new object[] { 2, "Drupal 6 Site Builder Solutions", "Mark Noble" });
        dt.AcceptChanges();

        Label1.Text = "This is 'Books' DataTable with 2 rows";

        GridView1.DataSource = dt;
        GridView1.DataBind();

        DataTable dt2 = dt.Clone();
        dt.TableName = "NewBooks";
        dt2.Rows.Add(new object[] { 1, "Flash with Drupal", "Travis Tidwell" });

        Label2.Text = "This is 'NewBooks' DataTable, clone of 'Books' DataTable";
        Label2.Text += "<br />Here we insert a new row";

        GridView2.DataSource = dt2;
        GridView2.DataBind();

        //this line merge dt2 with dt
        dt.Merge(dt2);

        Label3.Text = "Here we merge 'NewBooks' DataTable with 'Books' DataTable";
        GridView3.DataSource = dt;
        GridView3.DataBind();
    }
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
    <title>How to use DataTable Merge Method in ado.net</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <h2 style="color:DarkBlue; font-style:italic;">
            How to use DataTable Merge Method in ado.net
        </h2>
        <hr width="525" align="left" color="CornFlowerBlue" />
        <asp:Label
             ID="Label1"
             runat="server"
             Font-Size="Large"
             ForeColor="DodgerBlue"
             Font-Italic="true"
             >
        </asp:Label>
        <br />
        <asp:GridView 
            ID="GridView1"
            runat="server"
            BorderColor="Snow"
            ForeColor="Snow"
            Width="525"
            >
            <HeaderStyle BackColor="DarkOrchid" />
            <RowStyle BackColor="Tan" />
            <AlternatingRowStyle BackColor="BurlyWood" />
        </asp:GridView>
        <br />
        <asp:Label
             ID="Label2"
             runat="server"
             Font-Size="Large"
             ForeColor="DodgerBlue"
             Font-Italic="true"
             >
        </asp:Label>
        <br />
        <asp:GridView 
            ID="GridView2"
            runat="server"
            BorderColor="Snow"
            ForeColor="Snow"
            Width="525"
            >
            <HeaderStyle BackColor="DarkOrchid" />
            <RowStyle BackColor="Tan" />
            <AlternatingRowStyle BackColor="BurlyWood" />
        </asp:GridView>
        <br />
        <asp:Label
             ID="Label3"
             runat="server"
             Font-Size="Large"
             ForeColor="DodgerBlue"
             Font-Italic="true"
             >
        </asp:Label>
        <br />
        <asp:GridView 
            ID="GridView3"
            runat="server"
            BorderColor="Snow"
            ForeColor="Snow"
            Width="525"
            >
            <HeaderStyle BackColor="DarkOrchid" />
            <RowStyle BackColor="Tan" />
            <AlternatingRowStyle BackColor="BurlyWood" />
        </asp:GridView>
        <br />
        <asp:Button 
            ID="Button1"
            runat="server"
            OnClick="Button1_Click"
            Text="Populate GridView"
            Height="45"
            Font-Bold="true"
            ForeColor="DodgerBlue"
            />
    </div>
    </form>
</body>
</html>
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