Develop the Code for the Delete Button Click Event Handler – Insert, Update and Delete Data from Databases

7.6.3.2  Develop the Code for the Delete Button Click Event Handler
Open the Design View of our project, OracleCallableDelete, and double-click on the Delete button in the CourseFrame form window to open its event handler and enter the code shown in Figure 7.42 into this handler. Let’s have a close look at this piece of code to see how it works.

A. An if block is used to distinguish whether the Java Callable Method has been selected.

B. If it is, a new CallableStatement instance is declared.

FIGURE 7.42  The code for the Delete button click event handler.

C. A try-catch block is used to perform the data delete action using the CallableStatement method. The CallableStatement query string is created. Refer to Section 6.3.7.5.1 in Chapter 6 to get more detailed information about the structure and protocol of a CallableStatement query string. This is a dynamic query string with one positional parameter related to a new course; therefore, a question mark is used as the position holder for this parameter.

D. A new CallableStatement instance is created by calling the prepareCall() method that is defined in the Connection class.

E. The dynamic query string is initialized with a positional parameter, and the value of the parameter is selected by the user from the CourseList Listbox.

F. The CallableStatement instance is executed to call the stored procedure we built in the last section to delete the selected course record in the Course Table from our sample database.
G. The catch block is used to track and collect any possible exception for the data delete.
H. The deleted course _ id is removed from the Course ID field to indicate this delete action.

Let’s build and run the project to test the data delete function. Click on the Clean and Build Main Project button to build the project, and click on the Run Main Project button to run the project.

Enter a suitable username and password, such as jhenry and test, to the LogIn frame form and select the Course Information from the SelectFrame window to open the CourseFrame form window. Make sure that the Java Callable Method has been selected from the Query Method combo box. Then click on the Select button to query the default course information for the selected faculty member, Ying Bai.

Now select course CSE-549 from the CourseList Listbox and click on the Delete button to try to delete this course from the Course Table in our sample database.

To confirm and validate this data deletion action, click on the Select button again to try to retrieve all courses taught by the default faculty member, Ying Bai. It can be seen that there is no CSE-549 course in the CourseList Listbox, and this means that course CSE-549 has been deleted from the Course Table. You can also confirm this data delete action by opening the Course Table using the Services window in the Apache NetBeans IDE.

At this point, we have finished developing and building a data manipulation project using the CallableStatement object method. A complete project, OracleCallableDelete, can be found in the folder Class DB Projects\Chapter 7 in the Students folder at the CRC Press ftp site (refer to Figure 1.2 in Chapter 1).