C# 5.0 Programmer's Reference

712 ❘ APPENDIX A Solutions to Exercises
If a program creates a connection at the module level and uses the connection in multiple
methods, each method must be certain that it closes the connection before it exits. You
can use the finally section of a try-catch-finally block to ensure that the connection
is closed.
Alternatively you could use the following code to open the connection.
if (connection.State == ConnectionState.Closed) connection.Open();
6. The InsertThreeRecords example program does this. The following code shows its
InsertInstructorsRecord method.
// Insert an Instructors record.
private void InsertInstructorsRecord(OleDbConnection connection, int
instructorId, string firstName, string lastName, string department)
{
string insert =
"INSERT INTO Instructors (InstructorId, FirstName, LastName, Department)"
+ "VALUES (" + instructorId.ToString() + ", '"
firstName + "', '" + lastName + "', '" + department + "')";
using (OleDbCommand command = new OleDbCommand(insert, connection))
{
// Execute the command.
command.ExecuteNonQuery();
}
}
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If you omit the UPDATE statement’s WHERE clause, it updates all of the records in the table. In
this example, that means every instructor’s first name is changed to Fran.
7. The AdHocQuery example program does this. The following code shows how the program
displays a row’s values.
// Get the values.
object[] values = new object[reader.FieldCount];
reader.GetValues(values);
// Add the values to a string.
string result = "";
for (int i = 0; i < reader.FieldCount; i++)
{
result += values[i].ToString() + " ";
}
// Display the result.
resultsListBox.Items.Add(result);
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