Oracle C++ Call Interface Programmer's Guide

Using Object References
Nullness
WHERE name=’BEAR BYTE DATA MANAGEMENT’
This statement would return an embedded address object from the clients
table. The application could then use the values in the attributes of this object for
other processing. The application should execute the statement and fetch the object
in the same way as described in the section "Overview of Associative Access" on
page 3-13.
If a column in a row of a database table has no value, then that column is said to be
NULL, or to contain a NULL. Two different types of NULLs can apply to objects:
■ Any attribute of an object can have a NULL value. This indicates that the value
of that attribute of the object is not known.
■ An object may be atomically NULL. This means that the value of the entire
object is unknown.
Atomic nullness is not the same thing as nonexistence. An atomically NULL object
still exists, its value is just not known. It may be thought of as an existing object
with no data.
For every type of object attribute, OCCI provides a corresponding class. For
instance, NUMBER attribute type maps to the Number class, REF maps to RefAny,
and so on. Each and every OCCI class that represents a data type provides two
methods:
■ isNull — returns whether the object is null
■ setNull — sets the object to null
Similarly, these methods are inherited from the PObject class by all the objects and
can be used to access and set atomically null information about them.
Using Object References
OCCI provides the application with the flexibility to access the contents of the
objects using their pointers or their references. OCCI provides the
PObject::getRef method to return a reference to a persistent object. This call is
valid for persistent objects only.
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