Oracle C++ Call Interface Programmer's Guide

Working with Collections
Prefetching Complex Objects
After specifying and fetching a complex object, subsequent fetches of objects
contained in the complex object do not incur the cost of a network round-trip,
because these objects have already been prefetched and are in the object cache. Keep
in mind that excessive prefetching of objects can lead to a flooding of the object
cache. This flooding, in turn, may force out other objects that the application had
already pinned leading to a performance degradation instead of performance
improvement.
The SELECT privilege is needed for all prefetched objects. Objects in the complex
object for which the application does not have SELECT privilege will not be
prefetched.
Working with Collections
Oracle supports two kinds of collections - variable length arrays (ordered
collections) and nested tables (unordered collections). OCCI maps both of them to a
Standard Template Library (STL) vector container, giving you the full power,
flexibility, and speed of an STL vector to access and manipulate the collection
elements. The following is the SQL DDL to create a VARRAY and an object that
contains an attribute of type VARRAY.
CREATE TYPE ADDR_LIST AS VARRAY(3) OF REF ADDRESS;
CREATE TYPE PERSON AS OBJECT (name VARCHAR2(20), addr_l ADDR_LIST);
Here is the C++ class declaration generated by OTT:
class PERSON : public PObject
{
protected:
string name;
vector< Ref< ADDRESS > > addr_1;
public:
void *operator new(size_t size);
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Note: If there is insufficient memory in the object cache to hold all
prefetched objects, some objects may not be prefetched. The
application will then incur a network round-trip when those objects
are accessed later.