April 2003
Beginner to intermediate
380 pages
12h 25m
English
Content preview from Java Data ObjectsBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
Extent Access
An extent provides you with access to all the persistent instances
of a class and, optionally, its subclasses. You can iterate over the
elements of the extent or perform a query on the extent. The JDO
Extent interface represents the
extent of a class. Later in this chapter, we will discuss the IgnoreCache flag, which controls whether
instances made persistent or deleted during the current transaction are
contained in the extent.
You control whether an extent is maintained for a class in the
metadata. You use the metadata class
element’s requires-extent
attribute to indicate whether the persistent class has an extent. It has
a default value of "true“.
If your application does not need to iterate over the instances of
a class or perform a query on the extent, you can set the requires-extent attribute to "false" explicitly. Even if a class does not
have an extent, you can still make instances persistent, establish
references to them, and navigate to them in your application and
queries.
JDO 1.0.1 requires that if a class has a requires-extent set to "true“, none of its subclasses can set requires-extent to "false“. If your application specifies the
subclass’s parameter to be true when
calling the getExtent( ) method for a
base class, all subclass instances are included in the iteration of the
extent.
Accessing an Extent
You access the Extent
associated with a class by calling the following PersistenceManager method:
Extent getExtent(Class persistentClass, boolean subclasses); ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.