18 OCI Navigational and Type Functions

This chapter describes the OCI navigational functions which are used to navigate through objects retrieved from an Oracle database server. It also contains the descriptions of the functions which 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. The OCI provides a navigational interface to objects in the Oracle server. Those calls are described in this chapter.

The OCI object environment is initialized when the application calls OCIInitialize() 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. See Figure 18-1. 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 which 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 which 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 which 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 in-line attribute in an object. such as number or nested object, or an in-line element in a collection.

All values are considered to be transient by OCI, which means that OCI does not support automatic flushing a value to the database, and the client has to explicitly execute a SQL statement to store a value into the database. For embedded values, they are flushed when their containing instance are flushed.

Figure 18-1 shows how instances can be classified according to their type and lifetime:

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 illustrated by the following table:

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

In the remainder of this chapter, the following terms will be used:

An object can be 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), or marked updated or deleted.

See Also:
For a further discussion of the terms used to refer to different types of objects, please see "Persistent Objects, Transient Objects, and Values".

Conventions for OCI Functions

The entries for each function contain the following information:

Purpose

A brief description of what the function does.

Syntax

The function declaration.

Comments

Detailed information about the function if available. This may include restrictions on the use of the function, or other information that might be useful when using the function in an application.

Parameters

A description of each of the function's parameters. This includes the parameter's mode. The mode of a parameter has three possible values, as described next:

Table 18-2 Mode of a Parameter

Mode	Description
IN	A parameter that passes data to the OCI
OUT	A parameter that receives data from the OCI on this call
IN/OUT	A parameter that passes data on the call and receives data on the return from this or a subsequent call.

Returns

A description of what value is returned by the function if the function returns something other than the standard return codes listed in Table 19-2, "Function Return Values".

Related Functions

A list of related calls which may provide additional useful information.

Navigational Function Return Values

The OCI navigational functions typically return one of the following values:

Table 18-3 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, refer to Appendix C, "OCI Function Server Round Trips".

Navigational Function Error Codes

Table 18-4 lists the external Oracle error codes which can be returned by each of the OCI navigational functions. The list following the table identifies what each error represents.

Table 18-4 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
`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
`OCIOjectGetObjectRef()`	24350, 21560, 21710

The ORA errors in Table 18-4 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 - 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