Presents your 
JAVA E-NEWSLETTER for February 27, 2003

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USE AN OBJECT RELATIONAL MAPPING API TO WRITE JDBC CODE

Writing database and JDBC code can be tedious and prone to error. Object
Relational Mapping (ORM) tools or APIs can alleviate some of these
problems. Until recently, most of the available ORM tools were commercial and
very expensive. In the past year, however, a handful of open source ORM
tools and API's have become available.

Most of the popular ORM tools work by using a file or files to map Java
objects and relationships to a backend database. Depending on the tool,
you may have to create the files yourself; or the ORM tool may access your
database and automatically generate the files it needs to run against
your database schema.

After the mapping files are created, you can use them to generate source
code, or you can use the ORM tool's API directly and allow it to
generate the code it needs at runtime. After the mappings are set up and you've
decided how you'll interact with the ORM tool, you can begin to replace your
SQL code.

Here's a method that uses an ORM API to fetch a list of review objects
owned by a particular reviewer ID from a database:

public Collection getAllForReviewerId(int reviewerId) throws
              DaoException {
    Criteria criteria = new Criteria();
    criteria.addEqualTo("owner_id", new Integer(reviewerId));

    QueryByCriteria query =
         new QueryByCriteria(Review.class, criteria);

    query.setRequestedAttribute("owner_id");

    try {
        return broker.getCollectionByQuery(query);
    }
    catch (Throwable t) {
        t.printStackTrace();
    }

    return null;
}

All good ORM tools support the database functionality you'll require,
such as transactions, primary keys, foreign keys, and n-to-n relationships.
Examples of ORM tools and API's include the Apache DB Project's
ObJectRelationalBridge (OJB) and the open-source project Hibernate.

Apache DB Project's ObJectRelationalBridge (OJB)
http://db.apache.org/ojb/

Hibernate
http://cl.com.com/Click?q=26-KqRVIiMfeeZEsSnnZHJRZLebQ767 

Writing JDBC code can be a headache, but ORM APIs can lessen your
workload without incurring great expense, thanks to open source development.

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