Apple WebObjects 3.5 - Manual (Page 84)

Chapter 3 Creating a WebObjects Database Application
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1. Inspect the middle image button.
Its action attribute is bound to the action method saveChanges .
2. Look in the Main.java class to see how saveChanges is implemented.
The method (shown below with comments omitted) simply saves any
changes that have been made to
movieDisplayGroup ’s objects to the database.
public void saveChanges() throws Exception {
try {
this.session().defaultEditingContext().saveChanges();
}
catch (Exception exception) {
System.err.println("Cannot save changes ");
throw exception;
}
}
this.session() returns a Session object that represents a connection to the
application by a single user. A Session object provides access to an
EditingContext object. The expression
this.session().defaultEditingContext().saveChanges();
sends a saveChanges message to the Session’s defaultEditingContext . This default
EditingContext object manages graphs of objects fetched from the
database, and all changes to the database are saved through it. For more
information, see the EditingContext class specification in the Enterprise
Objects Framework Reference.
An EditingContext’s saveChanges method uses other Enterprise Objects
Framework objects to analyze its network of enterprise objects (Movie
objects referenced by the application) for changes and then to perform a set
of corresponding operations in the database. If an error occurs during this
process,
saveChanges throws an exception. Main.java ’s saveChanges method simply
raises the exception, having the effect of returning a diagnostic page. You
could return an error page that explains the reason for the save failure
instead, but the application in this tutorial uses the default behavior.
3. Inspect the first and third image buttons to see what their action attributes are
bound to.
They are bound to movieDisplayGroup.insert and movieDisplayGroup.delete ,
respectively. The DisplayGroup insert method creates a new enterprise
object, then inserts it into the display group’s list of objects just past the
current selection. The DisplayGroup
delete method deletes the display