updating a database [* Resolved *]

[steve_rm]

Hello,

I am developing a library system. I have 2 tables, book and student. The relationship is 1 student can have many books. I am having updating the book table when the student returns the book, the studentID (foreign key) will be cleared from the book table. I think this is the problem l am having. My code is listed below with the error description.

try
			{
				cnnReturnBook.ConnectionString = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\IBS Library System\LibrarySystem.mdb;Persist Security Info=False";
			
				//Find the book that have to be returned
				OleDbCommand cmdReturnBook = cnnReturnBook.CreateCommand();
				cmdReturnBook.CommandText = @"SELECT * FROM BOOK
											  WHERE RefNumber = '" + txtBookRef.Text + "' ";

				OleDbDataAdapter daReturnBook = new OleDbDataAdapter(cmdReturnBook);
				OleDbCommandBuilder cbReturnBook = new OleDbCommandBuilder(daReturnBook);

				if ( daReturnBook.Fill(dtReturnBook) == 1 )//Book has been found, there should be only one 1 record in the datatable
				{
					//Clear the text boxes
					txtDateOut.Text = "";
					txtDateDue.Text = "";
					txtStatus.Text = "Available"; //Show that the book is now available
					txtIDNumber.Text = ""; //ID number of the student who has this book.
					txtName.Text = "";
					txtSurname.Text = "";

					//Insert into the datatable row the new values
					dtReturnBook.Rows[0]["Status"] = txtStatus.Text;
					dtReturnBook.Rows[0]["DateOut"] = txtDateOut.Text;
					dtReturnBook.Rows[0]["Remarks"] = txtRemarks.Text;
					dtReturnBook.Rows[0]["StudentID"] = txtIDNumber.Text;
					dtReturnBook.Rows[0]["DateDue"] = txtDateDue.Text;

					daReturnBook.Update(dtReturnBook);//Error here
				}
			}
			catch ( OleDbException ex )
			{
				MessageBox.Show(ex.ToString(),"Exeception has occurred",MessageBoxButtons.OK,MessageBoxIcon.Warning);
			}
			catch ( Exception ex )
			{
				MessageBox.Show(ex.ToString(),"Exeception has occurred",MessageBoxButtons.OK, MessageBoxIcon.Warning);
			}
			finally 
			{
				cnnReturnBook.Dispose();
			}
		}

Error description
System.Data.OleDb.OleDbException: You cannot add or change a record because a related record is required in table 'Student'.
At System.Data.Common.DbDataAdapter.Update(DataRow[] dataRows, DataTableMapping tableMapping)
At System.Data.Common.DbDataAdapter.Update(DataTable dataTable)

Thanks in advance,

Steve