18 OCI Navigational and Type Functions

This chapter describes the OCI navigational functions that are used to navigate through objects retrieved from an Oracle database. It also contains the descriptions of the functions that are used to obtain type descriptor objects (TDOs).

Introduction to the Navigational and Type Functions

In an object navigational paradigm, data is represented as a graph of objects connected by references. Objects in the graph are reached by following the references. OCI provides a navigational interface to objects in an Oracle database. Those calls are described in this chapter.

The OCI object environment is initialized when the application calls OCIEnvCreate(), OCIEnvNlsCreate(), or OCIInitialize() (deprecated) in OCI_OBJECT mode.

Object Types and Lifetimes

An object instance is an occurrence of a type defined in an Oracle database. This section describes how an object instance can be represented in OCI. In OCI, an object instance can be classified based on the type, the lifetime, and referenceability:

A persistent object is an instance of an object type. A persistent object resides in a row of a table in the server and can exist longer than the duration of a session (connection). Persistent objects can be identified by object references that contain the object identifiers. A persistent object is obtained by pinning its object reference.
A transient object is an instance of an object type. A transient object cannot exist longer than the duration of a session, and it is used to contain temporary computing results. Transient objects can also be identified by references that contain transient object identifiers.
A value is an instance of a user-defined type (object type or collection type) or any built-in Oracle type. Unlike objects, values of object types are identified by memory pointers, rather than by references.

A value can be standalone or embedded. A standalone value is usually obtained by issuing a select statement. OCI also allows the client program to select a row of object table into a value by issuing a SQL statement. A referenceable object in the database can be represented as a value that cannot be identified by a reference. A standalone value can also be an out-of-line attribute in an object, such as VARCHAR or RAW, or an out-of-line element in a collection, such as VARCHAR, RAW, or object.

An embedded value is physically included in a containing instance. An embedded value can be an inline attribute in an object (such as number or nested object), or an inline element in a collection.

All values are considered to be transient by OCI, which means that OCI does not support automatic flushing of a value to the database, and the client must explicitly execute a SQL statement to store a value into the database. Embedded values are flushed when their containing instances are flushed.

Figure 18-1 shows how instances can be classified according to their type and lifetime. The type can be an object or the value of an object. The lifetime can be persistent (can exist longer than the duration of a session) or transient (can exist no long than the duration of the session).

Figure 18-1 Classification of Instances by Type and Lifetime

Description of "Figure 18-1 Classification of Instances by Type and Lifetime"

The distinction between various instances is further described in Table 18-1.

Table 18-1 Type and Lifetime of Instances

Characteristic	Persistent Object	Transient Object	Value
Type	object type	object type	object type, built-in, collection
Maximum Lifetime	until object is deleted	session	session
Referenceable	yes	yes	no
Embeddable	no	no	yes

Terminology

The remainder of this chapter uses the following terms:

An object is generally used to refer to a persistent object, a transient object, a standalone value of object type, or an embedded value of object type.
A referenceable object refers to a persistent object or a transient object.
A standalone object refers to a persistent object, a transient object, or a standalone value of object type.
An embedded object refers to a embedded value of object type.
An object is dirty if it has been created (newed), marked as updated, or marked as deleted.

See Also:
"Persistent Objects, Transient Objects, and Values" for further discussion of the terms used to refer to different types of objects

Conventions for OCI Functions

See the "Conventions for OCI Functions" for the conventions used in describing each function. The entries for each function may also contain the following information:

Return Values

A description of what value is returned by the function if the function returns something other then the standard codes listed in Table 18-3.

Navigational Function Return Values

Table 18-2 lists the values that OCI navigational functions typically return.

Table 18-2 Return Values of Navigational Functions

Return Value	Meaning
`OCI_SUCCESS`	The operation succeeded.
`OCI_ERROR`	The operation failed. The specific error can be retrieved by calling `OCIErrorGet()` on the error handle passed to the function.
`OCI_INVALID_HANDLE`	The OCI handle passed to the function is invalid.

Function-specific return information follows the description of each function in this chapter. Information about specific error codes returned by each function is presented in the following section.

Server Round-Trips for Cache and Object Functions

For a table showing the number of server round-trips required for individual OCI cache and object functions, see Table C-3.

Navigational Function Error Codes

Table 18-3 lists the external Oracle error codes that can be returned by each of the OCI navigational functions. The list following the table identifies what each error represents.

Table 18-3 OCI Navigational Functions Error Codes

Function	Possible ORA Errors
`OCICacheFlush()`	24350, 21560, 21705
`OCICacheFree()`	24350, 21560, 21705
`OCICacheRefresh()`	24350, 21560, 21705
`OCICacheUnmark()`	24350, 21560, 21705
`OCICacheUnpin()`	24350, 21560, 21705
`OCIObjectArrayPin()`	24350, 21560
`OCIObjectCopy()`	24350, 21560, 21705, 21710
`OCIObjectExists()`	24350, 21560, 21710
`OCIObjectFlush()`	24350, 21560, 21701, 21703, 21708, 21710
`OCIObjectFree()`	24350, 21560, 21603, 21710
`OCIObjectGetAttr()`	21560, 21600, 22305
`OCIObjectGetInd()`	24350, 21560, 21710
`OCIObjectGetObjectRef()`	24350, 21560, 21710
`OCIObjectGetTypeRef()`	24350, 21560, 21710
`OCIObjectIsDirty()`	24350, 21560, 21710
`OCIObjectIsLocked()`	24350, 21560, 21710
`OCIObjectLock()`	24350, 21560, 21701, 21708, 21710
`OCIObjectLockNoWait()`	24350, 21560, 21701, 21708, 21710
`OCIObjectMarkDelete()`	24350, 21560, 21700, 21701, 21702, 21710
`OCIObjectMarkDeleteByRef()`	24350, 21560
`OCIObjectMarkUpdate()`	24350, 21560, 21700, 21701, 21710
`OCIObjectNew()`	24350, 21560, 21705, 21710
`OCIObjectPin()`	24350, 21560, 21700, 21702
`OCIObjectPinCountReset()`	24350, 21560, 21710
`OCIObjectPinTable()`	24350, 21560, 21705
`OCIObjectRefresh()`	24350, 21560, 21709, 21710
`OCIObjectSetAttr()`	21560, 21600, 22305, 22279, 21601
`OCIObjectUnmark()`	24350, 21560, 21710
`OCIObjectUnmarkByRef()`	24350, 21560
`OCIObjectUnpin()`	24350, 21560, 21710

The ORA errors in Table 18-3 have the following meanings.

ORA-21560 - name argument should not be NULL
ORA-21600 - path expression too long
ORA-21601 - attribute is not an instance of user-defined type
ORA-21603 - cannot free a dirtied persistent object
ORA-21700 - object does not exist or has been deleted
ORA-21701 - invalid object
ORA-21702 - object is not instantiated in the cache
ORA-21703 - cannot flush an object that is not modified
ORA-21704 - cannot terminate cache or connection without flushing
ORA-21705 - service context is invalid
ORA-21708 - operations cannot be performed on a transient object
ORA-21709 - operations can only be performed on a current object
ORA-21710 - invalid pointer or value passed to the function
ORA-22279 - cannot perform operation with LOB buffering enabled
ORA-22305 - name argument is invalid
ORA-24350 - this OCI call is not allowed from external subroutines