I have written the code as below. here problem is that dt remain null. how to solve thst please tell me. public partial class Form1 : Form { private DataTable DTable; private DataRow drow; public Form1() { InitializeComponent(); } private OleDbConnection getConnection() { OleDbConnection con=new OleDbConnection (@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Documents and Settings\Administrator\My Documents\Visual Studio 2008\Projects\winApp for Student\winApp for Student\App_Data\SchooMgnSystem.mdb;Persist Security Info=True"); return con; } private void button1_Click(object sender, EventArgs e) { InsertData(); } private void InsertData() { if (DTable==null) { DTable = new DataTable(); DTable.Columns.Add("StudID", typeof(string)); DTable.Columns.Add("StudName", typeof (string)); DTable.Columns.Add("Address", typeof(string)); drow = DTable.NewRow(); drow[0] = txtStudID.Text; drow[1] = txtSTudName.Text; drow[2] = txtAddress.Text; DTable.Rows.Add(drow); grdStudent.DataSource = DTable; } else { drow = DTable.NewRow(); drow[0] = txtStudID.Text; drow[1] = txtSTudName.Text; drow[2] = txtAddress.Text; DTable.Rows.Add(drow); grdStudent.DataSource = DTable; } } private void button2_Click(object sender, EventArgs e) { string cmdstr; OleDbCommand cmd; OleDbConnection con = getConnection(); foreach (DataRow Drow in DTable.Rows) { cmdstr = "Insert into Student values('" + drow[0].ToString() + "','" + drow[1].ToString() + "','"+drow [2].ToString()+"')"; cmd = new OleDbCommand(cmdstr,con); try { con.Open(); cmd.ExecuteNonQuery(); } catch (Exception ex) { MessageBox.Show(ex.Message); } finally { con.Close(); } } }

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[ERROR] [main 11:01:20] (JCLLoggerAdapter.java:error:454) Unsuccessful: alter table user.CEN_USER_MASTER add constraint FKF4EDEDC3D0BAAE75 foreign key (ROLE_ID) references user.CEN_ROLE_MASTER [ERROR] [main 11:01:20] (JCLLoggerAdapter.java:error:454) ORA-02275: such a referential constraint already exists in the table

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