Java Data Objects (JDO) Make Persistence Easier

by David Wall

March 5, 2002 —

As a part of the javax.jdo package, Java Data Objects (JDO)
persistently store programmers' objects without worrying about a couple
of traditionally worrisome details:

* Translating your object model into a form that's compatible with
your database schema.
* Actually writing SQL statements that store data.

Its standard has just been finalized.

In an Enterprise JavaBeans environment, JDO gives you a new way to
implement bean-managed persistence in your entity beans. Rather than
requiring you to write JDBC code with its attendant SQL sentences, JDO
allows you to use a simpler, more Java-like syntax called Java Data
Objects Query Language (JDOQL) to manage the objects you've stored (and
want to store) under JDO control.

An SQL query for extracting a group of products with list prices in
excess of $25 would look like this:

SELECT * FROM ProductRoster WHERE listPrice > 25

The same query, expressed in the object-oriented terms of JDO, would
require this class:

class Product {
String name;
Float listPrice;
}

Then, you can query the set of existing products by using an instance
of the PersistenceManager class.

Class prodClass = Product.class;
Extent clnProduct = pm.getExtent (prodClass, false);
String filter = "listPrice > 25";
Query q = pm.newQuery (empClass, clnProduct, filter);
Collection products = q.execute ();

At the conclusion, products contains the JDO-managed persistent Product
objects that match your query.

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