6
Describing Schema
Metadata

This chapter discusses the use of the OCIDescribeAny() function to obtain information about schema elements.

The following topics are covered in this chapter:

Overview

This chapter deals with the use of the OCIDescribeAny() function to describe schema objects. For information about describing select-list items, refer to the section "Describing Select-List Items" on page 4-8.

For additional information about the OCIDescribeAny() call and its parameters, refer to the function description on page 13 - 34.

Using OCIDescribeAny()

The OCIDescribeAny() function allows you to perform an explicit describe of one of the following schema objects:

tables and views
synonyms
procedures
functions
packages
sequences
collections
types

Information about other schema elements (procedure/function arguments, columns, type attributes, and type methods) is available through a describe of one of the above schema objects. For example, when an application describes a table, it can then retrieve information about that table's columns.

The OCIDescribeAny() call requires a describe handle as one of its parameters. The describe handle must have been previously allocated with a call to OCIHandleAlloc(). After the call to OCIDescribeAny(), an application can retrieve information about the described object from the describe handle.

The information returned by OCIDescribeAny() is organized hierarchically like a tree. For example, the figure shows how description of a certain table might be organized:

The describe handle returned by OCIDescribeAny() points to such a tree of descriptions. Each node of the tree has attributes associated with the node and attributes (which are like recursive describe handles) that point to subtrees containing more information. If all the attributes are homogenous, as in case of elements of a list (e.g. column list), then we refer to them as parameters. In this document, we will use the terms handle and parameter interchangeably. The attributes associated with any node are returned by OCIAttrGet(), and the parameters are returned by OCIParamGet().

For example, an OCIAttrGet() on the describe handle for the table can return a handle to the column-list information. An application can then use OCIParamGet() to retrieve the handle to the column description of a particular column in the column-list. The handle to the column descriptor can be passed to OCIAttrGet() to get further information about the column.

No subsequent OCIAttrGet() or OCIParamGet() call requires extra round trips, as all the description is cached on the client side by OCIDescribeAny().

Restrictions

The OCIDescribeAny() call limits information returned to the basic information and stops expanding a node if it amounts to another describe. For example, if a table column is of an object type, then the OCI does not return a subtree describing the type since this information can be obtained by another describe.

For similar reasons, the OCI also does not allow describes on columns, arguments, or fields of tables, views, functions, procedures, or types. Such information can be obtained by describing the top-level object containing it.

Note on Datatype Codes

For more information about typecodes (e.g., the OCI_TYPCODE values returned in the OCI_ATTR_TYPECODE attribute, and the SQLT typecodes returned in the OCI_ATTR_DATA_TYPE attribute), refer to the section "Typecodes" on page 3-24.

OCI_ATTR_TYPECODE returns typecodes which represent the types supplied by the user when a new type is created (using the CREATE TYPE statement). These typecodes are of the enumerated type OCITypeCode, and are represented by OCI_TYPECODE constants. Internal PL/SQL types (boolean, indexed table) are not supported.

OCI_ATTR_DATA_TYPE returns typecodes which represent the datatypes stored in database columns. These are similar to the describe values returned by previous versions of Oracle. These values are represented by SQLT constants (ub2 values). BOOLEAN types return SQLT_BOL.

Note on Describing Types

In order to describe type objects, it is necessary to initialize the OCI process in object mode:

/* Initialize the OCI Process */ if (OCIInitialize((ub4) OCI_OBJECT, (dvoid *)0, (dvoid * (*)(dvoid *, size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t))0, (void (*)(dvoid *, dvoid *)) 0 )) { (void) printf("FAILED: OCIInitialize()\n"); return OCI_ERROR; }

Note on OCI_ATTR_LIST_ARGUMENTS

The OCI_ATTR_LIST_ARGUMENTS attribute for type methods represents "second-level" arguments for the method.

For example, given the following record my_type and the procedure my_proc which takes an argument of type my_type:

my_rec record(a number, b char)

my_proc (my_input my_rec)

the OCI_ATTR_LIST_ARGUMENTS attribute would apply to arguments a and b of the my_type record.

Parameter Attributes

A parameter is returned by OCIParamGet(). Parameters can describe different types of objects or information. Hence, parameters have attributes depending on the type of description they contain - these are the type-specific attributes. This section describes the attributes and handles that belong to different parameters.

The following table lists the attributes that belong to all parameters:

Table 6-1 Attributes Belonging to All Parameters

Attribute	Description	Datatype of Attribute
OCI_ATTR_PTYPE	type of information described by the parameter. Possible values are: OCI_PTYPE_TABLE - table OCI_PTYPE_VIEW - view OCI_PTYPE_PROC - procedure OCI_PTYPE_FUNC - function OCI_PTYPE_PKG - package OCI_PTYPE_TYPE - type OCI_PTYPE_TYPE_ATTR - attribute of a type OCI_PTYPE_TYPE_COLL - collection type information OCI_PTYPE_TYPE_METHOD - a method of a type OCI_PTYPE_SYN - synonym OCI_PTYPE_SEQ - sequence OCI_PTYPE_COL - column of a table or view OCI_PTYPE_ARG - argument of a function or procedure OCI_PTYPE_TYPE_ARG - argument of a type method OCI_PTYPE_TYPE_RESULT - the results of a method OCI_PTYPE_LIST - column list for tables and views, argument list for functions and procedures, or subprogram list for packages.	ub1














OCI_ATTR_TIMESTAMP	the timestamp of the object this description is based on (in Oracle date format)	ub1 *
OCI_ATTR_NUM_ATTRS	the number of attributes	ub2
OCI_ATTR_NUM_PARAMS	the number of parameters	ub2

The subsections that follow list the attributes and handles specific to different types of parameters.

Table/View Attributes

When a parameter is for a table or view (type OCI_PTYPE_TABLE or OCI_PTYPE_VIEW), it has the following type specific attributes:

Table 6-2 Attributes Belonging to Tables or Views

Attribute	Description	Datatype of Attribute
OCI_ATTR_OBJID	object id	ub4
OCI_ATTR_NUM_COLS	number of columns	ub2
OCI_ATTR_LIST_COLUMNS	column list (type OCI_PTYPE_LIST)	dvoid *

The following are additional attributes which belong to tables:

Table 6-3 Attributes Specific to Tables

Attribute	Description	Datatype of Attribute
OCI_ATTR_DBA	data block address of the segment header	ub4
OCI_ATTR_TABLESPACE	tablespace the table resides in	word
OCI_ATTR_CLUSTERED	whether the table is clustered	ub1
OCI_ATTR_PARTITIONED	whether the table is partitioned	ub1
OCI_ATTR_INDEX_ONLY	whether the table is index only	ub1

Procedure/Function Attributes

When a parameter is for a procedure or function (type OCI_PTYPE_PROC or OCI_PTYPE_FUNC), it has the following type specific attributes:

Table 6-4 Attribute Belonging to Procedures or Functions

Attribute	Description	Datatype of Attribute
OCI_ATTR_LIST_ARGUMENTS	argument list. See "List Attributes" on page 6-16.	dvoid *

The following attributes are defined only for package subprograms:

Table 6-5 Attributes Specific to Package Subprograms

Attribute	Description	Datatype of Attribute
OCI_ATTR_NAME	name of the procedure or function	text *
OCI_ATTR_OVERLOAD	overloading ID number (relevant in case the procedure or function is part of a package and is overloaded). Values returned may be different from direct query of a PL/SQL function or procedure.	ub2

Package Attributes

When a parameter is for a package (type OCI_PTYPE_PKG), it has the following type specific attributes:

Table 6-6 Attributes Belonging to Packages

Attribute	Description	Datatype of Attribute
OCI_ATTR_LIST_SUBPROGRAMS	subprogram list. See "List Attributes" on page 6-16.	dvoid *

Type Attributes

When a parameter is for a type (type OCI_PTYPE_TYPE), it has the attributes listed in Table 6-7. These attributes are only valid if the application initialized the OCI process in OCI_OBJECT mode in a call to OCIInitialize().

Table 6-7 Attributes Belonging to Types

Attribute	Description	Datatype of Attribute
OCI_ATTR_REF_TDO	returns the in-memory REF of the type descriptor object for the type, if the column type is an object type. If space has not been reserved for the OCIRef, then it is allocated implicitly in the cache. The caller can then pin the TDO with OCIObjectPin().	OCIRef *
OCI_ATTR_TYPECODE	typecode. See "Note on Datatype Codes" on page 6-4. Currently can be only OCI_TYPECODE_OBJECT or OCI_TYPECODE_NAMEDCOLLECTION.	OCITypeCode
OCI_ATTR_COLLECTION_TYPECODE	typecode of collection if type is collection; invalid otherwise. See "Note on Datatype Codes" on page 6-4. Currently can be only OCI_TYPECODE_VARRAY or OCI_TYPECODE_TABLE. An error is returned if this attribute is queried for a non-collection type.	OCITypeCode
OCI_ATTR_VERSION	a null terminated string containing the user-assigned version	text *
OCI_ATTR_IS_INCOMPLETE_TYPE	is this an incomplete type?	ub1
OCI_ATTR_IS_SYSTEM_TYPE	is this a system type?	ub1
OCI_ATTR_IS_PREDEFINED_TYPE	is this a predefined type?	ub1
OCI_ATTR_IS_TRANSIENT_TYPE	is this a transient type?	ub1
OCI_ATTR_IS_SYSTEM_ GENERATED_TYPE	is this a system-generated type?	ub1
OCI_ATTR_HAS_NESTED_TABLE	does this type contain a nested table attribute?	ub1
OCI_ATTR_HAS_LOB	does this type contain a LOB attribute?	ub1
OCI_ATTR_HAS_FILE	does this type contain a FILE attribute?	ub1
OCI_ATTR_COLLECTION_ELEMENT	handle to collection element. See "Collection Attributes" on page 6-11.	dvoid *
OCI_ATTR_NUM_TYPE_ATTRS	number of type attributes	ub4
OCI_ATTR_LIST_TYPE_ATTRS	list of type attributes. See "List Attributes" on page 6-16.	dvoid *
OCI_ATTR_NUM_TYPE_METHODS	number of type methods	ub4
OCI_ATTR_LIST_TYPE_METHODS	list of type methods. See "List Attributes" on page 6-16.	dvoid *
OCI_ATTR_MAP_METHOD	map method of type. See "Type Method Attributes" on page 6-10.	dvoid *
OCI_ATTR_ORDER_METHOD	order method of type. See "Type Method Attributes" on page 6-10.	dvoid *

Type Attribute Attributes

When a parameter is for an attribute of a type (type OCI_PTYPE_TYPE_ATTR), it has the attributes listed in Table 6-8.

Table 6-8 Attributes Belonging to Type Attributes

Attribute	Description	Datatype of Attribute
OCI_ATTR_DATA_SIZE	the maximum size of the type attribute. This length is returned in bytes and not characters for strings and raws. It returns 22 for NUMBERs.	ub2
OCI_ATTR_TYPECODE	typecode. See "Note on Datatype Codes" on page 6-4.	OCITypeCode
OCI_ATTR_DATA_TYPE	the data type of the type attribute. See "Note on Datatype Codes" on page 6-4.	ub2
OCI_ATTR_NAME	a pointer to a string which is the type attribute name	text *
OCI_ATTR_PRECISION	the precision of numeric type attributes. If a describe returns a value of zero for precision or -127 for scale, this indicates that the item being described is uninitialized; i.e., it is NULL in the data dictionary.	ub1
OCI_ATTR_SCALE	the scale of numeric type attributes. If a describe returns a value of zero for precision or -127 for scale, this indicates that the item being described is uninitialized; i.e., it is NULL in the data dictionary.	sb1
OCI_ATTR_TYPE_NAME	a string which is the type name. The returned value will contain the type name if the data type is SQLT_NTY or SQLT_REF. If the data type is SQLT_NTY, the name of the named data type's type is returned. If the data type is SQLT_REF, the type name of the named data type pointed to by the REF is returned	text *
OCI_ATTR_SCHEMA_NAME	a string with the schema name under which the type has been created	text *
OCI_ATTR_REF_TDO	returns the in-memory REF of the TDO for the type, if the column type is an object type. If space has not been reserved for the OCIRef, then it is allocated implicitly in the cache. The caller can then pin the TDO with OCIObjectPin().	OCIRef *
OCI_ATTR_CHARSET_ID	the character set id, if the type attribute is of a string/character type	ub2
OCI_ATTR_CHARSET_FORM	the character set form, if the type attribute is of a string/character type	ub1

Type Method Attributes

When a parameter is for a method of a type (type OCI_PTYPE_TYPE_METHOD), it has the attributes listed in Table 6-9.

Table 6-9 Attributes Belonging to Type Methods

Attribute	Description	Datatype of Attribute
OCI_ATTR_NAME	name of method (procedure or function)	text *
OCI_ATTR_ENCAPSULATION	encapsulation level of the method (either OCI_TYPEENCAP_PRIVATE or OCI_TYPEENCAP_PUBLIC)	OCITypeEncap
OCI_ATTR_LIST_ARGUMENTS	argument list. See "Note on OCI_ATTR_LIST_ARGUMENTS" on page 6-4, and "List Attributes" on page 6-16.	dvoid *
OCI_ATTR_IS_CONSTRUCTOR	is method a constructor?	ub1
OCI_ATTR_IS_DESTRUCTOR	is method a destructor?	ub1
OCI_ATTR_IS_OPERATOR	is method an operator?	ub1
OCI_ATTR_IS_SELFISH	is method selfish?	ub1
OCI_ATTR_IS_MAP	is method a map method?	ub1
OCI_ATTR_IS_ORDER	is method an order method?	ub1
OCI_ATTR_IS_RNDS	is "Read No Data State" set for method?	ub1
OCI_ATTR_IS_RNPS	is "Read No Process State" set for method?	ub1
OCI_ATTR_IS_WNDS	is "Write No Data State" set for method?	ub1
OCI_ATTR_IS_WNPS	is "Write No Process State" set for method?	ub1

As a reference, the following code shows the possible method flags which are used when determining the corresponding procedure/function attributes:

OCITypeMethodFlag

{ OCI_TYPEMETHOD_INLINE = 0x0001,                               /* inline */

  OCI_TYPEMETHOD_CONSTANT = 0x0002,                           /* constant */

  OCI_TYPEMETHOD_VIRTUAL = 0x0004,                             /* virtual */

  OCI_TYPEMETHOD_CONSTRUCTOR = 0x0008,                     /* constructor */

  OCI_TYPEMETHOD_DESTRUCTOR = 0x0010,                       /* destructor */

  OCI_TYPEMETHOD_OPERATOR  = 0x0020,                          /* operator */

  OCI_TYPEMETHOD_SELFISH = 0x0040,  /* selfish method (generic otherwise) */ 



  OCI_TYPEMETHOD_MAP = 0x0080,                 /* map (relative ordering) */

  OCI_TYPEMETHOD_ORDER  = 0x0100,            /* order (relative ordering) */

    /* OCI_TYPEMETHOD_MAP and OCI_TYPEMETHOD_ORDER are mutually exclusive */



  OCI_TYPEMETHOD_RNDS= 0x0200,            /* Read no Data State (default) */

  OCI_TYPEMETHOD_WNDS= 0x0400,                     /* Write no Data State */

  OCI_TYPEMETHOD_RNPS= 0x0800,                   /* Read no Process State */

  OCI_TYPEMETHOD_WNPS= 0x1000                   /* Write no Process State */ }

Collection Attributes

When a parameter is for a collection type (type OCI_PTYPE_COLL), it has the attributes listed in Table 6-10.

Table 6-10 Attributes Belonging to Collection Types

Attribute	Description	Datatype of Attribute
OCI_ATTR_DATA_SIZE	the maximum size of the type attribute. This length is returned in bytes and not characters for strings and raws. It returns 22 for NUMBERs.	ub2
OCI_ATTR_TYPECODE	typecode. See "Note on Datatype Codes" on page 6-4.	OCITypeCode
OCI_ATTR_DATA_TYPE	the data type of the type attribute. See "Note on Datatype Codes" on page 6-4.	ub2
OCI_ATTR_NUM_ELEMENTS	the number of elements in an array. It is only valid for collections that are arrays	ub4
OCI_ATTR_NAME	a pointer to a string which is the type attribute name	text *
OCI_ATTR_PRECISION	the precision of numeric type attributes. If a describe returns a value of zero for precision or -127 for scale, this indicates that the item being described is uninitialized; i.e., it is NULL in the data dictionary.	ub1
OCI_ATTR_SCALE	the scale of numeric type attributes. If a describe returns a value of zero for precision or -127 for scale, this indicates that the item being described is uninitialized; i.e., it is NULL in the data dictionary.	sb1
OCI_ATTR_TYPE_NAME	a string which is the type name. The returned value will contain the type name if the data type is SQLT_NTY or SQLT_REF. If the data type is SQLT_NTY, the name of the named data type's type is returned. If the data type is SQLT_REF, the type name of the named data type pointed to by the REF is returned	text *
OCI_ATTR_SCHEMA_NAME	a string with the schema name under which the type has been created	text *
OCI_ATTR_REF_TDO	returns the in-memory REF of the TDO for the type, if the column type is an object type. If space has not been reserved for the OCIRef, then it is allocated implicitly in the cache. The caller can then pin the TDO with OCIObjectPin().	OCIRef *
OCI_ATTR_CHARSET_ID	the character set id, if the type attribute is of a string/character type	ub2
OCI_ATTR_CHARSET_FORM	the character set form, if the type attribute is of a string/character type	ub1

Synonym Attributes

When a parameter is for a synonym (type OCI_PTYPE_SYN), it has the attributes listed in Table 6-11.

Table 6-11 Attributes Belonging to Synonyms

Attribute	Description	Datatype of Attribute
OCI_ATTR_OBJID	object id	ub4
OCI_ATTR_SCHEMA	a null-terminated string containing the schema name of the synonym translation	text *
OCI_ATTR_NAME	a null-terminated string containing the object name of the synonym translation	text *
OCI_ATTR_LINK	a null-terminated string containing the database link name of the synonym translation	text *

Sequence Attributes

When a parameter is for a sequence (type OCI_PTYPE_SEQ), it has the attributes listed in

Table 6-12 Attributes Belonging to Sequences

Attribute	Description	Datatype of Attribute
OCI_ATTR_OBJID	object id	ub4
OCI_ATTR_MIN	minimum value (in Oracle number format)	ub1 *
OCI_ATTR_MAX	maximum value (in Oracle number format)	ub1 *
OCI_ATTR_INCR	increment (in Oracle number format)	ub1 *
OCI_ATTR_CACHE	number of sequence numbers cached; zero if the sequence is not a cached sequence (in Oracle number format)	ub1 *
OCI_ATTR_ORDER	whether the sequence is ordered	ub1
OCI_ATTR_HW_MARK	high-water mark (in Oracle number format)	ub1 *

Table 6-12.

Column Attributes

When a parameter is for a column of a table or view (type OCI_PTYPE_COL), it has the attributes listed in

Table 6-13 Attributes Belonging to Columns of Tables or Views

Attribute	Description	Datatype of Attribute
OCI_ATTR_DATA_SIZE	the maximum size of the column. This length is returned in bytes and not characters for strings and raws. It returns 22 for NUMBERs.	ub2
OCI_ATTR_DATA_TYPE	the data type of the column. See "Note on Datatype Codes" on page 6-4.	ub2
OCI_ATTR_NAME	a pointer to a string which is the column name	text *
OCI_ATTR_PRECISION	the precision of numeric columns. If a describe returns a value of zero for precision or -127 for scale, this indicates that the item being described is uninitialized; i.e., it is NULL in the data dictionary.	ub1
OCI_ATTR_SCALE	the scale of numeric columns. If a describe returns a value of zero for precision or -127 for scale, this indicates that the item being described is uninitialized; i.e., it is NULL in the data dictionary.	sb1
OCI_ATTR_IS_NULL	returns 0 if null values are not permitted for the column	ub1
OCI_ATTR_TYPE_NAME	returns a string which is the type name. The returned value will contain the type name if the data type is SQLT_NTY or SQLT_REF. If the data type is SQLT_NTY, the name of the named data type's type is returned. If the data type is SQLT_REF, the type name of the named data type pointed to by the REF is returned	text *
OCI_ATTR_SCHEMA_NAME	returns a string with the schema name under which the type has been created	text *
OCI_ATTR_REF_TDO	the REF of the TDO for the type, if the column type is an object type	OCIRef *
OCI_ATTR_CHARSET_ID	the character set id, if the column is of a string/character type	ub2
OCI_ATTR_CHARSET_FORM	the character set form, if the column is of a string/character type	ub1

Table 6-13.

Argument/Result Attributes

When a parameter is for an argument of a procedure/function (type OCI_PTYPE_ARG), for a type method argument (type OCI_PTYPE_TYPE_ARG) or for method results (type OCI_PTYPE_TYPE_RESULT), it has the attributes listed in

Table 6-14 Attributes Belonging to Arguments/Results

Attribute	Description	Datatype of Attribute
OCI_ATTR_NAME	returns a pointer to a string which is the argument name	text *
OCI_ATTR_POSITION	the position of the argument in the argument list. Always returns zero.	ub2
OCI_ATTR_TYPECODE	typecode. See "Note on Datatype Codes" on page 6-4.	OCITypeCode
OCI_ATTR_DATA_TYPE	the data type of the argument. See "Note on Datatype Codes" on page 6-4.	ub2
OCI_ATTR_DATA_SIZE	the size of the data type of the argument. This length is returned in bytes and not characters for strings and raws. It returns 22 for NUMBERs.	ub2
OCI_ATTR_PRECISION	the precision of numeric arguments. If a describe returns a value of zero for precision or -127 for scale, this indicates that the item being described is uninitialized; i.e., it is NULL in the data dictionary.	ub1
OCI_ATTR_SCALE	the scale of numeric arguments. If a describe returns a value of zero for precision or -127 for scale, this indicates that the item being described is uninitialized; i.e., it is NULL in the data dictionary.	sb1
OCI_ATTR_LEVEL	the data type levels. This attribute always returns zero.	ub2
OCI_ATTR_HAS_DEFAULT	indicates whether an argument has a default	ub1
OCI_ATTR_IOMODE	indicates the argument modet: 0 is IN (OCI_TYPEPARAM_IN), 1 is OUT (OCI_TYPEPARAM_OUT), 2 is IN/OUT (OCI_TYPEPARAM_INOUT)	OCITypeParamMode
OCI_ATTR_RADIX	returns a radix (if number type)	ub1
OCI_ATTR_IS_NULL	returns 0 if null values are not permitted for the column	ub1
OCI_ATTR_TYPE_NAME	returns a string which is the type name, or the package name in the case of package local types. The returned value will contain the type name if the data type is SQLT_NTY or SQLT_REF. If the data type is SQLT_NTY, the name of the named data type's type is returned. If the data type is SQLT_REF, the type name of the named data type pointed to by the REF is returned.	text *
OCI_ATTR_SCHEMA_NAME	for SQLT_NTY or SQLT_REF, returns a string with the schema name under which the type was created, or under which the package was created in the case of package local types	text *
OCI_ATTR_SUB_NAME	for SQLT_NTY or SQLT_REF, returns a string with the type name, in the case of package local types	text *
OCI_ATTR_LINK	for SQLT_NTY or SQLT_REF, returns a string with the database link name of the database on which the type exists. This can happen only in the case of package local types, when the package is remote.	text *
OCI_ATTR_REF_TDO	returns the REF of the TDO for the type, if the argument type is an object	OCIRef *
OCI_ATTR_CHARSET_ID	returns the character set ID if the argument is of a string/character type	ub2
OCI_ATTR_CHARSET_FORM	returns the character set form if the argument is of a string/character type	ub1

Table 6-14.

List Attributes

When a parameter is for a list of columns, arguments, or subprograms (type OCI_PTYPE_LIST), it has the following type specific attributes and handles (parameters):

The list has an OCI_ATTR_LIST_TYPE attribute which designates the list type. The possible values are:
- OCI_LTYPE_COL - column list
- OCI_LTYPE_ARG_PROC - procedure argument list
- OCI_LTYPE_ARG_FUNC - function argument list
- OCI_LTYPE_SUBPRG - subprogram list
- OCI_LTYPE_TYPE_ATTR - type attribute list
- OCI_LTYPE_TYPE_METHOD - type method list
- OCI_LTYPE_TYPE_ARG_PROC - type method without result argument list
- OCI_LTYPE_TYPE_ARG_FUNC - type method without result argument list
The list has an OCI_ATTR_NUM_PARAMS attribute, which tells the number of elements in the list.
The list has 1..OCI_ATTR_NUM_PARAMS parameters for each of the columns, arguments, or subprograms in the list (type OCI_PTYPE_COL, OCI_PTYPE_ARG, OCI_PTYPE_PROC, or OCI_PTYPE_FUNC). In the case of a function argument list, position 0 has a parameter for the return value (type OCI_PTYPE_ARG).

Examples

The following examples demonstrate the use of OCIDescribeAny() for describing different types of schema objects. For a more detailed code sample, refer to "Example 4, Describing an Object" on page D-47.

Retrieving column data types for a table

This example illustrates the use of an explicit describe. Let us take an example application, which needs to retrieve the column datatypes for a table. The following pseudo-code shows how an application would be able to use the describe interface:

text objptr[] = <table-name>;

ub4 objp_len = strlen(<table_name>);

OCIParam *parmh; 		/* parameter handle */

OCIParam *collsthd; /* handle to list of columns */

OCIParam *colhd; 				 /* column handle */

/* get the describe handle for the table */
if (OCIDescribeAny(svch, errh, objptr, objp_len, OCI_OTYPE_NAME, 0, 

          OCI_PTYPE_TABLE, 		&dschp))
          return error;
/* get the parameter handle */
if (OCIAttrGet(dschp, OCI_HTYPE_DESCRIBE, &parmh, 0, OCI_ATTR_PARAM,

          errh))
        return error;
/* The type information of the object, in this case, OCI_PTYPE_TABLE,

is obtained from the parameter descriptor returned by the OCIAttrGet */
/* get the number of columns in the table */
if (OCIAttrGet(parmh, OCI_DTYPE_PARAM, &numcols, 0, 

          OCI_ATTR_NUM_COLS, errh))
        return error;
/* get the handle to the column list of the table */
if (OCIAttrGet(parmh, OCI_DTYPE_PARAM, &collsthd, 0,

          OCI_ATTR_LIST_COLUMNS, errh)==OCI_NO_DATA)
      return error;
/* go through the column list and retrieve the data-type of each column,

and then recursively describe column types. */

for (i = 1; i <= numcols; i++)
{
        /* get parameter for column i */
        if (OCIParamGet(collsthd, OCI_DTYPE_PARAM, errh, &colhd, i))
                return error;
        /* for example, get data type for ith column */
        if (OCIAttrGet(colhd, OCI_DTYPE_PARAM, &datatype[i-1], 0,

              OCI_ATTR_DATA_TYPE, errh))
                return error	;
}

Describing the stored procedure

Let us consider a stored procedure or a function.The difference between a procedure and a function is that the latter has a return type at position 0 in the argument list, while the former has no argument associated with position 0 in the argument list. The steps required to describe type methods (also divided into functions and procedures) are identical to that of regular PL/SQL functions and procedures. Note that procedures/functions can take default types of objects as arguments. Let us consider a procedure

P1 (arg1 emp.sal%type, arg2 emp%rowtype).

Furthermore, let us assume that each row in emp table has two columns name (VARCHAR2(20)), and sal (NUMBER). Thus, in the argument list for P1, we have two arguments, arg1 and arg2, at positions 1 and 2 respectively at level 0, and arguments name and sal at positions 1and 2 respectively at level 1. Description of P1 returns the number of arguments as two while returning the higher level (> 0) arguments as attributes of the 0 zero level arguments.

The following psuedocode elucidates the description of P1.

text objptr[] = "P1"; 	 	/* procedure name */

ub4 objp_len = strlen("P1");

OCIParam *parmh; 		/* parameter handle */

OCIParam *arglst; 				 		 / * list of args */

OCIParam *arg; 			 	/* argument handle */

ub2 numargs, pos, level; 

text *name;

ub4 namelen;



/* get the describe handle for the table */

if (OCIDescribeAny(svch, errh, objptr, objp_len, OCI_OTYPE_NAME, 0, 

        OCI_PTYPE_PROC, 		&dschp))
        return error;



/* get the parameter handle */

if (OCIAttrGet(dschp, OCI_HTYPE_DESCRIBE, &parmh, 0, OCI_ATTR_PARAM, 

        errh))
        return error;



/* Get the number of arguments and the arg list */

if (OCIAttrGet (parmh, OCI_DTYPE_PARAM, &arglst, 

		0, OCI_ATTR_LIST_ARGUMENTS, errh))
        return error;
if (OCIAttrGet (parmh, OCI_DTYPE_PARAM, &numargs, 0, 

        OCI_ATTR_NUM_PARAMS, errh))
        return error;



/* For a procedure, we begin with i = 1; for a 

	function, we begin with i = 0. */



for (i = 1; i < numargs; i++) {

	OCIParamGet (arglst, OCI_DTYPE_PARAM, errh, &arg, i);

	OCIAttrGet (arg, OCI_DTYPE_PARAM, &name, &namelen, OCI_ATTR_NAME, 

                errh);

...
/* to print the attributes of the argument of type record 

(arguments at the next level), 	traverse the argument list */



	OCIAttrGet (arg, OCI_DTYPE_PARAM, &arglst1, 0,

		OCI_ATTR_LIST_ARGUMENTS, erh);

	

/* check if the current argument is a record. For arg1 in P1

arglst1 is NULL. */



    if (arglst1) {

        OCIAttrGet (	arg, OCI_DTYPE_PARAM, &numargs1,			0, OCI_ATTR_NUM_PARAMS, 

                errh);



/* Note that for both functions and procedures,			the next higher level 

arguments start from 			index 1. For arg2 in P1, the number of 					arguments at 

the level 1 would be 2 */



        for (i = 1; i < numargs1, i++) {

            OCIParamGet (arglst1, OCI_DTYPE_PARAM, 						errh, 		&arg1, i);

            OCIAttrGet (arg1, OCI_DTYPE_PARAM, &name1, 				&namelen1, 

                OCI_ATTR_NAME, errh);
        ...
        }

    }

}

Retrieving attributes of an object type

This example illustrates the use of an explicit describe on a named object type. We illustrate how you can describe an object by its name or by its object reference (OCIRef). The following pseudo-code attempts to retrieve the data type value each of the object type's attribute. It is very similar to the first example on page 6 - 17.

text type_name[] = <type_name>;

ub4 type_name_len = strlen(<type_name>);

OCIRef *type_ref = <type_ref>;

un4 numattrs;

OCIDescribe *dschp; /* describe handle */

OCIParam *parmh; 		/* parameter handle */

OCIParam *attrlsthd; /* handle to list of attrs */

OCIParam *attrhd; 			/* attribute handle */



/* allocate describe handle */

if (OCIHandleAlloc((dvoid *)envh, (dvoid **)&dschp,

                  	(ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (dvoid **)0))

    return error;



/* get the describe handle for the type */

if (describe_by_name)

    if (OCIDescribeAny(svch, errh, (dvoid*)type_name, type_name_len, 

              OCI_OTYPE_NAME, 0, OCI_PTYPE_TYPE, 		dschp))
              return error;

else

    if (OCIDescribeAny(svch, errh, (dvoid*)type_ref, 0, OCI_OTYPE_REF, 

                0, OCI_PTYPE_TYPE, 		dschp))
                return error;





/* get the parameter handle */

if (OCIAttrGet(dschp, OCI_HTYPE_DESCRIBE, &parmh, 0, OCI_ATTR_PARAM, 

        errh))
        return error;



/* The type information of the object, in this case, OCI_PTYPE_TYPE, is 

obtained from the parameter descriptor returned by the OCIAttrGet */



/* get the number of attributes in the type */

if (OCIAttrGet(parmh, OCI_DTYPE_PARAM, &numattrs, 0, 

        OCI_ATTR_NUM_TYPE_ATTRS, errh))
        return error;



/* get the handle to the attribute list of the type */

if (OCIAttrGet(parmh, OCI_DTYPE_PARAM, (dvoid *)&attrlsthd, 0, 			

            OCI_ATTR_LIST_TYPE_ATTRS, errh)==OCI_NO_DATA)

    return error;



/* go through the attribute list and retrieve the data-type of each 
attribute, and then recursively describe attribute types. */



for (i = 1; i <= numattrs; i++)

{

		/* get parameter for attribute i */

		if (OCIParamGet(attrlsthd, OCI_DTYPE_PARAM, errh, &attrhd, i))

            return error;



		/* for example, get data type and typecode for attribute; note that 
OCI_ATTR_DATA_TYPE returns the SQLT code, while OCI_ATTR_TYPECODE returns 
the Oracle Type System typecode. */
		if (OCIAttrGet(attrhd, OCI_DTYPE_PARAM,			&datatype[i-1], 0, 

            OCI_ATTR_DATA_TYPE,			errh))
        return error;
		/* for example, get data type for attribute*/

		if (OCIAttrGet(attrhd, OCI_DTYPE_PARAM,			&typecode[i-1], 0, 

            OCI_ATTR_TYPECODE, errh))
        return error;



		/* if attribute is an object type, recursively describe it */

		if (typecode[i-1] == OCI_TYPECODE_OBJECT)

		{

			OCIRef *attr_type_ref;

			OCIDescribe *nested_dschp;



			/* allocate describe handle */

			if (OCIHandleAlloc((dvoid *)envh,						(dvoid**)&dschp,

				(ub4)OCI_HTYPE_DESCRIBE,				(size_t)0, (dvoid **)0))

				return error;



			if (OCIAttrGet(attrhd, OCI_DTYPE_PARAM,

                    &attr_type_ref, 0, OCI_ATTR_REF_TDO,				errh))
            return error;
            OCIDescribeAny(svch, errh,				(dvoid*)attr_type_ref, 0, 

                    OCI_OTYPE_REF, 0, OCI_PTYPE_TYPE, 		nested_dschp);
/* go on describing the type... */

        }

}

Retrieving the collection element's data type of a named collection type

This example illustrates the use of an explicit describe on a named collection type. We illustrate how you can describe an object by its name or by its object reference (OCIRef). The following pseudo-code attempts to retrieve the data type value each of the object type's attribute. It is very similar to the first example on page 6 - 17.

text type_name[] = <type_name>;

ub4 type_name_len = strlen(<type_name>);

OCIRef *type_ref = <type_ref>;

un4 numattrs;

OCIDescribe *dschp; /* describe handle */

OCIParam *parmh; 		/* parameter handle */

OCIParam *attrlsthd; /* handle to list of attrs */

OCIParam *attrhd; 			/* attribute handle */



/* allocate describe handle */

if (OCIHandleAlloc((dvoid *)envh, (dvoid **)&dschp,

                  	(ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (dvoid **)0))

    return error;



/* get the describe handle for the type */

if (describe_by_name)

    if (OCIDescribeAny(svch, errh, (dvoid*)type_name, type_name_len, 

            OCI_OTYPE_NAME, 0, OCI_PTYPE_TYPE, 		dschp))
            return error;

else

    if (OCIDescribeAny(svch, errh, (dvoid*)type_ref, 0, OCI_OTYPE_REF, 0, 

            OCI_PTYPE_TYPE, 		&dschp))
            return error;



/* get the parameter handle */

if (OCIAttrGet(dschp, OCI_HTYPE_DESCRIBE, &parmh, 0, OCI_ATTR_PARAM, 

        errh))
        return error;



/* get the Oracle Type System type code of the type to determine that 
this is a collection type */

if (OCIAttrGet(attrhd, OCI_DTYPE_PARAM,			&typecode, 0, OCI_ATTR_TYPECODE, 

        errh))
        return error;



/* if typecode is OCI_TYPECODE_NAMEDCOLLECTION,

    proceed to describe collection element */

if (typecode == OCI_TYPECODE_NAMEDCOLLECTION)

{

    /* get the collection's type: ie, OCI_TYPECODE_VARRAY or 
OCI_TYPECODE_TABLE */

if (OCIAttrGet(parmh, OCI_DTYPE_PARAM, 	(dvoid *)&collection_typecode, 0, 
OCI_ATTR_COLLECTION_TYPECODE, errh))
        return error;
/* get the collection element; you MUST use this to further retrieve 
information about the collection's element */
if (OCIAttrGet(parmh, OCI_DTYPE_PARAM, 	&collection_element_parmh, 0, 
OCI_ATTR_COLLECTION_ELEMENT, errh))
        return error;
/* get the number of elements if collection is a VARRAY; not valid for 
nested tables */

if (collection_typecode == OCI_TYPECODE_VARRAY)

        if OCIAttrGet(collection_element_parmh, 	OCI_DTYPE_PARAM,

            (dvoid *)&num_elements, 0, OCI_ATTR_NUM_ELEMENTS, errh))
            return error;
/* now use the collection_element parameter handle to retrieve 
information about the collection element */

if OCIAttrGet(collection_element_parmh, OCI_DTYPE_PARAM, 

        (dvoid *)&element_typecode, 0, OCI_ATTR_TYPECODE, errh))
        return error;
/* do the same to describe additional collection element information; 
this is very similar to describing type attributes */

}

6 Describing Schema Metadata