Java Programming with Oracle JDBC

Refs

A java.sql.Ref is an object that holds a reference to a database object. Depending on how you implement your Oracle objects, a Ref may hold a global unique identifier (GUID) or a primary key column, and may also contain a ROWID. But what it contains is moot. It’s how you use a Ref that’s important. A Ref object is simply an address to a database object. With it, you can retrieve, or materialize, an object value. And with Oracle’s implementation, oracle.sql.REF, you can also update a value. But you can’t create a new database reference in your Java program. That simply doesn’t make any sense. Since a reference points to a location of an object in the database, the database has to create a reference when an object is inserted, and then you must retrieve the newly created object’s reference into a Ref object, similar to how we handled a Blob or Clob in Chapter 12.

References can also be stored as attributes in other database objects to establish relationships between objects. In this chapter, we’ll cover how to retrieve a reference into a Ref object, how to use it to materialize an object value, and finally, how to use it to update a database object. So let’s start with retrieving a reference.

Retrieving a Reference

To retrieve a reference from a database, use the ref( ) database function. Do you remember how you used the value( ) function? Well, you use the ref( ) database function the same way. You use it in a SELECT statement, passing it an alias for a table name. For example, ...