Oracle® Call Interface Programmer's Guide, 10g Release 2 (10.2) Part Number B14250-02 |
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This chapter discusses the use of the OCIDescribeAny() function to obtain information about schema elements.
This chapter contains these topics:
The OCIDescribeAny()
function enables you to perform an explicit describe of the following schema objects and their subschema objects:
Information about other schema elements (function arguments, columns, type attributes, and type methods) is available through a describe of one of the preceding schema objects or an explicit describe of the subschema object.
When an application describes a table, it can then retrieve information about that table's columns. Additionally, OCIDescribeAny()
can directly describe subschema objects such as columns of a table, packages of a function, or fields of a type if given the name of the subschema object.
The OCIDescribeAny()
call requires a describe handle as one of its arguments. The describe handle must be previously allocated with a call to OCIHandleAlloc().
The information returned by OCIDescribeAny()
is organized hierarchically like a tree, as shown in Figure 6-1:
Figure 6-1 OCIDescribeAny() Table Description
The describe handle returned by OCIDescribeAny()
has an attribute, OCI_ATTR_PARAM
, that points to such a description tree. Each node of the tree has attributes associated with that node, and attributes that are like recursive describe handles and point to subtrees containing further information. If all the attributes are homogenous, as in the case of elements of a column list, they are called parameters. The attributes associated with any node are returned by OCIAttrGet()
, and the parameters are returned by OCIParamGet()
.
A call to OCIAttrGet()
on the describe handle for the table returns 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, such as the name and datatype.
After a SQL statement is executed, information about the select-list is available as an attribute of the statement handle. No explicit describe call is needed. To retrieve information about select-list items from the statement handle, the application must call OCIParamGet()
once for each position in the select-list to allocate a parameter descriptor for that position.
Note:
No subsequentOCIAttrGet()
or OCIParamGet()
call requires extra round trips, as all the description is cached on the client side by OCIDescribeAny()
.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.
The table name is not returned by OCIDescribeAny()
or the implicit use of OCIStmtExecute()
. Sometimes a column is not associated with a table. In most cases, the table is already known.
When performing describe operations, you should be aware of the following:
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.
See Also:
"Typecodes" for more information about typecodes, such as theOCI_TYPCODE
values returned in the OCI_ATTR_TYPECODE
attribute and the SQLT typecodes returned in the OCI_ATTR_DATA_TYPE
attributeIn order to describe type objects, it is necessary to initialize the OCI process in object mode:
/* Initialize the OCI Process */ if (OCIEnvCreate((OCIEnv **) &envhp, (ub4) OCI_OBJECT, (dvoid *) 0, (dvoid * (*)(dvoid *,size_t)) 0, (dvoid * (*)(dvoid *, dvoid *, size_t)) 0, (void (*)(dvoid *, dvoid *)) 0, (size_t) 0, (dvoid **) 0)) { printf("FAILED: OCIEnvCreate()\n"); return OCI_ERROR; }
See Also:
"OCIInitialize()"The column attribute OCI_ATTR_PRECISION
can be returned using an implicit describe with OCIStmtExecute()
and an explicit describe with OCIDescribeAny()
. When using an implicit describe, the precision should be set to sb2
. When using an explicit describe, the precision should be set to ub1
for a placeholder. This is necessary to match the datatype of precision in the dictionary.
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_type record(a number, b char) my_proc (my_input my_type)
the OCI_ATTR_LIST_ARGUMENTS
attribute would apply to arguments a
and b
of the my_type
record.
A parameter is returned by OCIParamGet()
. Parameters can describe different types of objects or information, and have attributes depending on the type of description they contain, or type-specific attributes. This section describes the attributes and handles that belong to different parameters.
Note that OCIDescribeAny()
does support more than two name components, for example, schema.type.attr1.attr2.method1
. Note that with more than one component, the first component is interpreted as the schema name (unless some other flag is set). There is a flag to specify that the object must be looked up under PUBLIC, that is, describe "a", where "a" can be either in the current schema or a public synonym.
If you do not know what the object type is, specify OCI_PTYPE_UNK
. Otherwise an error is returned if the actual object type does not match the specified type.
Table 6-1 lists the attributes of all parameters:
Table 6-1 Attributes of All Parameters
Attribute | Description | Attribute Datatype |
---|---|---|
The number of parameters |
ub2 |
|
Object or schema ID |
ub4 |
|
Database name or object name in a schema |
OraText * |
|
Schema name where the object is located |
OraText * |
|
Type of information described by the parameter. Possible values:
|
ub1 |
|
The timestamp of the object on which the description is based in Oracle date format |
ub1 * |
The following sections list the attributes and handles specific to different types of parameters.
Parameters for a table or view (type OCI_PTYPE_TABLE
or OCI_PTYPE_VIEW
) have the following type-specific attributes:
Table 6-2 Attributes of Tables or Views
Attribute | Description | Attribute Datatype |
---|---|---|
Object id |
ub4 |
|
Number of columns |
ub2 |
|
Column list (type |
dvoid * |
|
REF to the TDO of the base type in case of extent tables |
OCIRef* |
|
Indicates the table is temporary |
ub1 |
|
|
Indicates the table is typed |
ub1 |
Duration of a temporary table. Values can be:
|
OCIDuration |
The following are additional attributes which belong to tables:
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 of Procedures or Functions
Attribute | Description | Attribute Datatype |
---|---|---|
Argument list. See "List Attributes". |
dvoid * |
|
Indicates the procedure or function has invoker's rights |
ub1 |
The following attributes are defined only for package subprograms:
Table 6-5 Attributes Specific to Package Subprograms
Attribute | Description | Attribute Datatype |
---|---|---|
Name of the procedure or function |
OraText * |
|
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 |
When a parameter is for a package (type OCI_PTYPE_PKG
), it has the following type specific attributes:
Table 6-6 Attributes of Packages
Attribute | Description | Attribute Datatype |
---|---|---|
Subprogram list. See "List Attributes". |
dvoid * |
|
Is the package invoker's rights? |
ub1 |
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 of Types
Attribute | Description | Attribute Datatype |
---|---|---|
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 |
OCIRef * |
|
Typecode. See "Datatype Codes". Currently can be only |
OCITypeCode |
|
Typecode of collection if type is collection; invalid otherwise. See "Datatype Codes". Currently can be only |
OCITypeCode |
|
Indicates this is an incomplete type |
ub1 |
|
Indicates this is a system type |
ub1 |
|
Indicates this is a predefined type |
ub1 |
|
Indicates this is a transient type |
ub1 |
|
Indicates this is a system-generated type |
ub1 |
|
This type contains a nested table attribute |
ub1 |
|
This type contains a LOB attribute |
ub1 |
|
This type contains a |
ub1 |
|
Handle to collection element. See "Collection Attributes". |
dvoid * |
|
Number of type attributes |
ub2 |
|
List of type attributes. See "List Attributes". |
dvoid * |
|
Number of type methods |
ub2 |
|
List of type methods. See "List Attributes". |
dvoid * |
|
Map method of type. See "Type Method Attributes". |
dvoid * |
|
Order method of type. See "Type Method Attributes". |
dvoid * |
|
Indicates the type has invoker's rights |
ub1 |
|
A pointer to a string which is the type attribute name |
OraText * |
|
A string with the schema name where the type has been created |
OraText * |
|
Indicates this is a final type |
ub1 |
|
Indicates this is an instantiable type |
ub1 |
|
Indicates this is a subtype |
ub1 |
|
Name of the schema that contains the supertype |
OraText * |
|
Name of the supertype |
OraText * |
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 of Type Attributes
Attribute | Description | Attribute Datatype |
---|---|---|
The maximum size of the type attribute. This length is returned in bytes and not characters for strings and raws. It returns 22 for |
ub4 |
|
Typecode. See "Datatype Codes". |
OCITypeCode |
|
The datatype of the type attribute. See "Datatype Codes". |
ub2 |
|
A pointer to a string which is the type attribute name |
OraText * |
|
The precision of numeric type attributes. If the precision is nonzero and scale is -127, then it is a |
ub1 for explicit describe sb2 for implicit describe |
|
The scale of numeric type attributes. If the precision is nonzero and scale is -127, then it is a |
sb1 |
|
A string which is the type name. The returned value will contain the type name if the datatype is |
OraText * |
|
A string with the schema name under which the type has been created |
OraText * |
|
Returns the in-memory |
OCIRef * |
|
The character set id, if the type attribute is of a string/character type |
ub2 |
|
The character set form, if the type attribute is of a string/character type |
ub1 |
|
The fractional seconds precision of a datetime or interval. |
ub1 |
|
The leading field precision of an interval. |
ub1 |
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 of Type Methods
Attribute | Description | Attribute Datatype |
---|---|---|
Name of method (procedure or function) |
OraText * |
|
Encapsulation level of the method (either |
OCITypeEncap |
|
Argument list. See "Note on OCI_ATTR_LIST_ARGUMENTS", and "List Attributes". |
dvoid * |
|
Indicates method is a constructor |
ub1 |
|
Indicates method is a destructor |
ub1 |
|
Indicates method is an operator |
ub1 |
|
Indicates method is selfish |
ub1 |
|
Indicates method is a map method |
ub1 |
|
Indicates method is an order method |
ub1 |
|
Indicates "Read No Data State" is set for method |
ub1 |
|
Indicates "Read No Process State" is set for method |
ub1 |
|
Indicates "Write No Data State" is set for method |
ub1 |
|
Indicates "Write No Process State" is set for method |
ub1 |
|
Indicates this is a final method |
ub1 |
|
Indicates this is an instantiable method |
ub1 |
|
Indicates this is an overriding method |
ub1 |
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 of Collection Types
Attribute | Description | Attribute Datatype |
---|---|---|
The maximum size of the type attribute. This length is returned in bytes and not characters for strings and raws. It returns 22 for |
ub4 |
|
Typecode. See "Datatype Codes". |
OCITypeCode |
|
The datatype of the type attribute. See "Datatype Codes". |
ub2 |
|
The number of elements in an array. It is only valid for collections that are arrays |
ub4 |
|
A pointer to a string which is the type attribute name |
OraText * |
|
The precision of numeric type attributes. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a |
ub1 for explicit describe sb2 for implicit describe |
|
The scale of numeric type attributes. If the precision is nonzero and scale is -127, then it is a |
sb1 |
|
A string which is the type name. The returned value will contain the type name if the datatype is |
OraText * |
|
A string with the schema name under which the type has been created |
OraText * |
|
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 |
OCIRef * |
|
The character set id, if the type attribute is of a string/character type |
ub2 |
|
The character set form, if the type attribute is of a string/character type |
ub1 |
When a parameter is for a synonym (type OCI_PTYPE_SYN
), it has the attributes listed in Table 6-11.
Table 6-11 Attributes of Synonyms
Attribute | Description | Attribute Datatype |
---|---|---|
Object id |
ub4 |
|
A string containing the schema name of the synonym translation |
OraText * |
|
A |
OraText * |
|
A |
OraText * |
When a parameter is for a sequence (type OCI_PTYPE_SEQ
), it has the attributes listed in Table 6-12.
Table 6-12 Attributes of Sequences
Attribute | Description | Attribute Datatype |
---|---|---|
Object id |
ub4 |
|
Minimum value (in Oracle |
ub1 * |
|
Maximum value (in Oracle |
ub1 * |
|
Increment (in Oracle |
ub1 * |
|
Number of sequence numbers cached; zero if the sequence is not a cached sequence (in Oracle |
ub1 * |
|
Whether the sequence is ordered |
ub1 |
|
High-water mark (in |
ub1 * |
See Also:
"OCINumber Examples"Note:
For BINARY_FLOAT and BINARY_DOUBLE:If OCIDescribeAny()
is used to retrieve the column datatype (OCI_ATTR_DATA_TYPE
) for BINARY_FLOAT
or BINARY_DOUBLE
columns in a table, it returns the internal datatype code.
The SQLT codes corresponding to the internal datatype codes for BINARY_FLOAT
and BINARY_DOUBLE
are SQLT_IBFLOAT
and SQLT_IBDOUBLE
.
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.
Table 6-13 Attributes of Columns of Tables or Views
Attribute | Description | Attribute Datatype |
---|---|---|
Returns the type of length semantics of the column. 0 means byte-length semantics and 1 means character-length semantics. See "Character Length Semantics Support in Describing". |
ub4 |
|
Returns the column character length which is the number of characters allowed in the column. It is the counterpart of |
ub2 |
|
The maximum size of the column. This length is returned in bytes and not characters for strings and raws. It returns 22 for |
ub4 |
|
The datatype of the column. See "Datatype Codes". |
ub2 |
|
A pointer to a string which is the column name |
OraText * |
|
The precision of numeric columns. If the precision is nonzero and scale is -127, then it is a |
ub1 for explicit describe sb2 for implicit describe |
|
The scale of numeric columns. If the precision is nonzero and scale is -127, then it is a FLOAT, else it is a |
sb1 |
|
Returns 0 if null values are not permitted for the column |
ub1 |
|
Returns a string which is the type name. The returned value will contain the type name if the datatype is |
OraText * |
|
Returns a string with the schema name under which the type has been created |
OraText * |
|
The |
OCIRef * |
|
The character set id, if the column is of a string/character type |
ub2 |
|
The character set form, if the column is of a string/character type |
ub1 |
When a parameter is for an argument of a procedure or 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.
Table 6-14 Attributes of Arguments and Results
Attribute | Description | Attribute Datatype |
---|---|---|
Returns a pointer to a string which is the argument name |
OraText * |
|
The position of the argument in the argument list. Always returns zero. |
ub2 |
|
Typecode. See "Datatype Codes". |
OCITypeCode |
|
The datatype of the argument. See "Datatype Codes". |
ub2 |
|
The size of the datatype of the argument. This length is returned in bytes and not characters for strings and raws. It returns 22 for |
ub4 |
|
The precision of numeric arguments. If the precision is nonzero and scale is -127, then it is a |
|
|
The scale of numeric arguments. If the precision is nonzero and scale is -127, then it is a |
|
|
The datatype levels. This attribute always returns zero. |
ub2 |
|
Indicates whether an argument has a default |
ub1 |
|
|
The list of arguments at the next level (when the argument is of a record or table type). |
dvoid * |
Indicates the argument mode: 0 is IN ( 1 is OUT ( 2 is IN/OUT ( |
OCITypeParamMode |
|
Returns a radix (if number type) |
ub1 |
|
Returns 0 if null values are not permitted for the column |
ub1 |
|
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 datatype is SQLT_NTY or SQLT_REF. If the datatype is SQLT_NTY, the name of the named datatype's type is returned. If the datatype is SQLT_REF, the type name of the named datatype pointed to by the REF is returned. |
OraText * |
|
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 |
OraText * |
|
For SQLT_NTY or SQLT_REF, returns a string with the type name, in the case of package local types |
OraText * |
|
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. |
OraText * |
|
Returns the REF of the TDO for the type, if the argument type is an object |
OCIRef * |
|
Returns the character set ID if the argument is of a string/character type |
ub2 |
|
Returns the character set form if the argument is of a string/character type |
ub1 |
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 and their lower bounds when traversing the list are:
Table 6-15 List Attributes
The list has an OCI_ATTR_NUM_PARAMS
attribute, which tells the number of elements in the list.
Each list has LowerBound
.. OCI_ATTR_NUM_PARAMS
parameters. LowerBound
is the value in the Lower Bound column of Table 6-15, "List Attributes". In the case of a function argument list, position 0 has a parameter for the return value (type OCI_PTYPE_ARG
).
When a parameter is for a schema type (type OCI_PTYPE_SCHEMA
), it has the attributes listed in Table 6-16:
When a parameter is for a database type (type OCI_PTYPE_DATABASE
), it has the attributes listed in Table 6-17:
Table 6-17 Attributes Specific to Databases
Attribute | Description | Attribute Datatype |
---|---|---|
Database version |
OraText * |
|
Database character set Id from the server handle |
ub2 |
|
Database character set Id from the server handle |
ub2 |
|
List of schemas (type |
ub1 |
|
Maximum length of a procedure name |
ub4 |
|
Maximum length of a column name |
ub4 |
|
How a COMMIT operation affects cursors and prepared statements in the database. Values are:
|
ub1 |
|
Maximum length of a catalog (database) name |
ub1 |
|
Position of the catalog in a qualified table. Values are |
ub1 |
|
Does database support savepoints? Values are |
ub1 |
|
Does database support the nowait clause? Values are |
ub1 |
|
Is autocommit mode required for DDL statements? Values are |
ub1 |
|
Locking mode for the database. Values are |
ub1 |
When a parameter is for a rule (type OCI_PTYPE_RULE
), it has the attributes listed in Table 6-18:
Table 6-18 Attributes Specific to Rules
Attribute | Description | Attribute Datatype |
---|---|---|
Rule condition |
OraText * |
|
Owner name of evaluation context associated with the rule, if any |
OraText * |
|
Object name of evaluation context associated with the rule, if any |
OraText * |
|
Comment associated with the rule, if any |
OraText * |
|
List of name value pairs in the action context (type |
dvoid * |
When a parameter is for a rule set (type OCI_PTYPE_RULE_SET
), it has the attributes listed in Table 6-19:
Table 6-19 Attributes Specific to Rule Sets
Attribute | Description | Attribute Datatype |
---|---|---|
Owner name of evaluation context associated with the rule set, if any |
OraText * |
|
Object name of evaluation context associated with the rule set, if any |
OraText * |
|
Comment associated with the rule set, if any |
OraText * |
|
List of rules in the rule set (type |
dvoid * |
When a parameter is for an evaluation context (type OCI_PTYPE_EVALUATION_CONTEXT
), it has the attributes listed in Table 6-20:
Table 6-20 Attributes Specific to Evaluation Contexts
Attribute | Description | Attribute Datatype |
---|---|---|
Evaluation function associated with the evaluation context, if any |
OraText * |
|
Comment associated with the evaluation context, if any |
OraText * |
|
List of table aliases in the evaluation context (type |
dvoid * |
|
List of variable types in the evaluation context (type |
dvoid * |
When a parameter is for a table alias (type OCI_PTYPE_TABLE_ALIAS
), it has the attributes listed in Table 6-21:
When a parameter is for a variable (type OCI_PTYPE_VARIABLE_TYPE
), it has the attributes listed in Table 6-22:
Table 6-22 Attributes Specific to Variable Types
When a parameter is for a name value pair (type OCI_PTYPE_NAME_VALUE
), it has the attributes listed in Table 6-23:
Since release Oracle9i, query and column information are supported with character length semantics.
The following attributes of describe handles support character length semantics:
OCI_ATTR_CHAR_SIZE gets the column character length, which is the number of characters allowed in the column. It is the counterpart of OCI_ATTR_DATA_SIZE
that gets the byte length.
Calling OCIAttrGet()
with attribute OCI_ATTR_CHAR_SIZE
or OCI_ATTR_DATA_SIZE
does not return data on stored procedure parameters, because stored procedure parameters are not bounded.
OCI_ATTR_CHAR_USED
gets the type of length semantics of the column. 0 means byte-length semantics and 1 means character length semantics.
An application can describe a select-list query either implicitly or explicitly through OCIStmtExecute()
. Other schema elements must be described explicitly through OCIDescribeAny()
.
If the database column was created using character length semantics, then the implicit describe information will contain the character length, the byte length, and a flag indicating how the database column was created. OCI_ATTR_CHAR_SIZE
is the character length of the column or expression. The OCI_ATTR_CHAR_USED
flag is 1 in this case, indicating that the column or expression was created with character length semantics.
The OCI_ATTR_DATA_SIZE
value will be always large enough to hold all the data, as many as OCI_ATTR_CHAR_SIZE
number of characters. The OCI_ATTR_DATA_SIZE
will be usually set to (OCI_ATTR_CHAR_SIZE
)*(the client's max bytes) for each character value.
If the database column was created with byte length semantics, then the implicit describe will behave exactly as it does before release 9.0. That is, the OCI_ATTR_DATA_SIZE
value returned will be (column's byte length)*(the maximum conversion ratio between the client and server's character set), that is, column byte length divided by the server's max bytes for each character multiplied by the client's max bytes for each character. The OCI_ATTR_CHAR_USED
value is 0 and the OCI_ATTR_CHAR_SIZE
value will be set to the same value as OCI_ATTR_DATA_SIZE
.
Explicit describes of tables will have the following attributes:
OCI_ATTR_DATA_SIZE
that gets the column's size in bytes, as it appears in the server
the length in characters in OCI_ATTR_CHAR_SIZE
a flag OCI_ATTR_CHAR_USED
that indicates how the column was created
When inserting, if the OCI_ATTR_CHAR_USED
flag is set, you can set the OCI_ATTR_MAXCHAR_SIZE
in the bind handle to the value returned by OCI_ATTR_CHAR_SIZE
in the parameter handle. This will prevent you from violating the size constraint for the column.
See Also:
"IN Binds"When an Oracle9i or later client talks to an Oracle8i or earlier server, it will behave as if the database is only using byte length semantics;
When an Oracle8i or earlier client talks to a Oracle9i or later server, the attributes OCI_ATTR_CHAR_SIZE
and OCI_ATTR_CHAR_USED
are not available on the client side.
In both cases, the character length semantics cannot be described when either the server or client has an Oracle8i or earlier software release.
The following examples demonstrate the use of OCIDescribeAny()
for describing different types of schema objects. For a more detailed code sample, see the demonstration program cdemodsa.c
included with your Oracle installation.
See Also:
For additional information on the demonstration programs, see Appendix B, "OCI Demonstration Programs"This example illustrates the use of an explicit describe that retrieves the column datatypes for a table.
... int i=0; text objptr[] = "EMPLOYEES"; /* the name of a table to be described */ ub2 numcols, col_width; ub1 char_semantics; ub2 coltyp; ub4 objp_len = (ub4) strlen((char *)objptr); OCIParam *parmh = (OCIParam *) 0; /* parameter handle */ OCIParam *collsthd = (OCIParam *) 0; /* handle to list of columns */ OCIParam *colhd = (OCIParam *) 0; /* column handle */ OCIDescribe *dschp = (OCIDescribe *)0; /* describe handle */ OCIHandleAlloc((dvoid *)envhp, (dvoid **)&dschp, (ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (dvoid **)0); /* get the describe handle for the table */ if (OCIDescribeAny(svch, errh, (dvoid *)objptr, objp_len, OCI_OTYPE_NAME, 0, OCI_PTYPE_TABLE, dschp)) return OCI_ERROR; /* get the parameter handle */ if (OCIAttrGet((dvoid *)dschp, OCI_HTYPE_DESCRIBE, (dvoid *)&parmh, (ub4 *)0, OCI_ATTR_PARAM, errh)) return OCI_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 */ numcols = 0; if (OCIAttrGet((dvoid *)parmh, OCI_DTYPE_PARAM, (dvoid *)&numcols, (ub4 *)0, OCI_ATTR_NUM_COLS, errh)) return OCI_ERROR; /* get the handle to the column list of the table */ if (OCIAttrGet((dvoid *)parmh, OCI_DTYPE_PARAM, (dvoid *)&collsthd, (ub4 *)0, OCI_ATTR_LIST_COLUMNS, errh)==OCI_NO_DATA) return OCI_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((dvoid *)collsthd, OCI_DTYPE_PARAM, errh, (dvoid **)&colhd, (ub4)i)) return OCI_ERROR; /* for example, get datatype for ith column */ coltyp = 0; if (OCIAttrGet((dvoid *)colhd, OCI_DTYPE_PARAM, (dvoid *)&coltyp, (ub4 *)0, OCI_ATTR_DATA_TYPE, errh)) return OCI_ERROR; /* Retrieve the length semantics for the column */ char_semantics = 0; OCIAttrGet((dvoid*) colhd, (ub4) OCI_DTYPE_PARAM, (dvoid*) &char_semantics,(ub4 *) 0, (ub4) OCI_ATTR_CHAR_USED, (OCIError *) errh); col_width = 0; if (char_semantics) /* Retrieve the column width in characters */ OCIAttrGet((dvoid*) colhd, (ub4) OCI_DTYPE_PARAM, (dvoid*) &col_width, (ub4 *) 0, (ub4) OCI_ATTR_CHAR_SIZE, (OCIError *) errh); else /* Retrieve the column width in bytes */ OCIAttrGet((dvoid*) colhd, (ub4) OCI_DTYPE_PARAM, (dvoid*) &col_width,(ub4 *) 0, (ub4) OCI_ATTR_DATA_SIZE, (OCIError *) errh); } if (dschp) OCIHandleFree((dvoid *) dschp, OCI_HTYPE_DESCRIBE); ...
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 and functions can take default types of objects as arguments. Consider the following procedure:
P1 (arg1 emp.sal%type, arg2 emp%rowtype)
Assume that each row in emp table has two columns: name(VARCHAR2(20))
, and sal(NUMBER)
. In the argument list for P1
, there are 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.
... int i = 0, j = 0; text objptr[] = "add_job_history"; /* the name of a procedure to be described */ ub4 objp_len = (ub4)strlen((char *)objptr); ub2 numargs = 0, numargs1, pos, level; text *name, *name1; ub4 namelen, namelen1; OCIParam *parmh = (OCIParam *) 0; /* parameter handle */ OCIParam *arglst = (OCIParam *) 0; /* list of args */ OCIParam *arg = (OCIParam *) 0; /* argument handle */ OCIParam *arglst1 = (OCIParam *) 0; /* list of args */ OCIParam *arg1 = (OCIParam *) 0; /* argument handle */ OCIDescribe *dschp = (OCIDescribe *)0; /* describe handle */ OCIHandleAlloc((dvoid *)envhp, (dvoid **)&dschp, (ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (dvoid **)0); /* get the describe handle for the procedure */ if (OCIDescribeAny(svch, errh, (dvoid *)objptr, objp_len, OCI_OTYPE_NAME, 0, OCI_PTYPE_PROC, dschp)) return OCI_ERROR; /* get the parameter handle */ if (OCIAttrGet((dvoid *)dschp, OCI_HTYPE_DESCRIBE, (dvoid *)&parmh, (ub4 *)0, OCI_ATTR_PARAM, errh)) return OCI_ERROR; /* Get the number of arguments and the arg list */ if (OCIAttrGet((dvoid *)parmh, OCI_DTYPE_PARAM, (dvoid *)&arglst, (ub4 *)0, OCI_ATTR_LIST_ARGUMENTS, errh)) return OCI_ERROR; if (OCIAttrGet((dvoid *)arglst, OCI_DTYPE_PARAM, (dvoid *)&numargs, (ub4 *)0, OCI_ATTR_NUM_PARAMS, errh)) return OCI_ERROR; /* For a procedure, we begin with i = 1; for a function, we begin with i = 0. */ for (i = 1; i <= numargs; i++) { OCIParamGet ((dvoid *)arglst, OCI_DTYPE_PARAM, errh, (dvoid **)&arg, (ub4)i); namelen = 0; OCIAttrGet((dvoid *)arg, OCI_DTYPE_PARAM, (dvoid *)&name, (ub4 *)&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((dvoid *)arg, OCI_DTYPE_PARAM, (dvoid *)&arglst1, (ub4 *)0, OCI_ATTR_LIST_ARGUMENTS, errh); /* check if the current argument is a record. For arg1 in the procedure arglst1 is NULL. */ if (arglst1) { numargs1 = 0; OCIAttrGet((dvoid *)arglst1, OCI_DTYPE_PARAM, (dvoid *)&numargs1, (ub4 *)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 the procedure, the number of arguments at the level 1 would be 2 */ for (j = 1; j <= numargs1; j++) { OCIParamGet((dvoid *)arglst1, OCI_DTYPE_PARAM, errh, (dvoid **)&arg1, (ub4)j); namelen1 = 0; OCIAttrGet((dvoid *)arg1, OCI_DTYPE_PARAM, (dvoid *)&name1, (ub4 *)&namelen1, OCI_ATTR_NAME, errh); } } } if (dschp) OCIHandleFree((dvoid *) dschp, OCI_HTYPE_DESCRIBE); ...
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 code fragment attempts to retrieve the datatype value of each of the object type's attributes.
... int i = 0; text type_name[] = "inventory_typ"; ub4 type_name_len = (ub4)strlen((char *)type_name); OCIRef *type_ref = (OCIRef *) 0; ub2 numattrs = 0, describe_by_name = 1; ub2 datatype = 0; OCITypeCode typecode = 0; OCIDescribe *dschp = (OCIDescribe *) 0; /* describe handle */ OCIParam *parmh = (OCIParam *) 0; /* parameter handle */ OCIParam *attrlsthd = (OCIParam *) 0; /* handle to list of attrs */ OCIParam *attrhd = (OCIParam *) 0; /* attribute handle */ /* allocate describe handle */ if (OCIHandleAlloc((dvoid *)envh, (dvoid **)&dschp, (ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (dvoid **)0)) return OCI_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 OCI_ERROR; } else { /* get ref to type using OCIAttrGet */ /* get the describe handle for the type */ if (OCIDescribeAny(svch, errh, (dvoid*)type_ref, 0, OCI_OTYPE_REF, 0, OCI_PTYPE_TYPE, dschp)) return OCI_ERROR; } /* get the parameter handle */ if (OCIAttrGet((dvoid *)dschp, OCI_HTYPE_DESCRIBE, (dvoid *)&parmh, (ub4 *)0, OCI_ATTR_PARAM, errh)) return OCI_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((dvoid *)parmh, OCI_DTYPE_PARAM, (dvoid *)&numattrs, (ub4 *)0, OCI_ATTR_NUM_TYPE_ATTRS, errh)) return OCI_ERROR; /* get the handle to the attribute list of the type */ if (OCIAttrGet((dvoid *)parmh, OCI_DTYPE_PARAM, (dvoid *)&attrlsthd, (ub4 *)0, OCI_ATTR_LIST_TYPE_ATTRS, errh)) return OCI_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((dvoid *)attrlsthd, OCI_DTYPE_PARAM, errh, (dvoid **)&attrhd, i)) return OCI_ERROR; /* for example, get datatype and typecode for attribute; note that OCI_ATTR_DATA_TYPE returns the SQLT code, while OCI_ATTR_TYPECODE returns the Oracle Type System typecode. */ datatype = 0; if (OCIAttrGet((dvoid *)attrhd, OCI_DTYPE_PARAM, (dvoid *)&datatype, (ub4 *)0, OCI_ATTR_DATA_TYPE,errh)) return OCI_ERROR; typecode = 0; if (OCIAttrGet((dvoid *)attrhd, OCI_DTYPE_PARAM,(dvoid *)&typecode, (ub4 *)0, OCI_ATTR_TYPECODE, errh)) return OCI_ERROR; /* if attribute is an object type, recursively describe it */ if (typecode == OCI_TYPECODE_OBJECT) { OCIRef *attr_type_ref; OCIDescribe *nested_dschp; /* allocate describe handle */ if (OCIHandleAlloc((dvoid *)envh,(dvoid**)&nested_dschp, (ub4)OCI_HTYPE_DESCRIBE,(size_t)0, (dvoid **)0)) return OCI_ERROR; if (OCIAttrGet((dvoid *)attrhd, OCI_DTYPE_PARAM, (dvoid *)&attr_type_ref, (ub4 *)0, OCI_ATTR_REF_TDO,errh)) return OCI_ERROR; OCIDescribeAny(svch, errh,(dvoid*)attr_type_ref, 0, OCI_OTYPE_REF, 0, OCI_PTYPE_TYPE, nested_dschp); /* go on describing the attribute type... */ } } if (dschp) OCIHandleFree((dvoid *) dschp, OCI_HTYPE_DESCRIBE); ...
This example illustrates the use of an explicit describe on a named collection type:
text type_name[] = "phone_list_typ"; ub4 type_name_len = (ub4) strlen((char *)type_name); OCIRef *type_ref = (OCIRef *) 0; ub2 describe_by_name = 1; ub4 num_elements = 0; OCITypeCode typecode = 0, collection_typecode = 0, element_typecode = 0; dvoid *collection_element_parmh = (dvoid *) 0; OCIDescribe *dschp = (OCIDescribe *) 0; /* describe handle */ OCIParam *parmh = (OCIParam *) 0; /* parameter handle */ /* allocate describe handle */ if (OCIHandleAlloc((dvoid *)envh, (dvoid **)&dschp, (ub4)OCI_HTYPE_DESCRIBE, (size_t)0, (dvoid **)0)) return OCI_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 OCI_ERROR; } else { /* get ref to type using OCIAttrGet */ /* get the describe handle for the type */ if (OCIDescribeAny(svch, errh, (dvoid*)type_ref, 0, OCI_OTYPE_REF, 0, OCI_PTYPE_TYPE, dschp)) return OCI_ERROR; } /* get the parameter handle */ if (OCIAttrGet((dvoid *)dschp, OCI_HTYPE_DESCRIBE, (dvoid *)&parmh, (ub4 *)0, OCI_ATTR_PARAM, errh)) return OCI_ERROR; /* get the Oracle Type System type code of the type to determine that this is a collection type */ typecode = 0; if (OCIAttrGet((dvoid *)parmh, OCI_DTYPE_PARAM,(dvoid *)&typecode, (ub4 *)0, OCI_ATTR_TYPECODE, errh)) return OCI_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 */ collection_typecode = 0; if (OCIAttrGet((dvoid *)parmh, OCI_DTYPE_PARAM, (dvoid *)&collection_typecode, (ub4 *)0, OCI_ATTR_COLLECTION_TYPECODE, errh)) return OCI_ERROR; /* get the collection element; you MUST use this to further retrieve information about the collection's element */ if (OCIAttrGet((dvoid *)parmh, OCI_DTYPE_PARAM, &collection_element_parmh, (ub4 *)0, OCI_ATTR_COLLECTION_ELEMENT, errh)) return OCI_ERROR; /* get the number of elements if collection is a VARRAY; not valid for nested tables */ if (collection_typecode == OCI_TYPECODE_VARRAY) { if (OCIAttrGet((dvoid *)collection_element_parmh, OCI_DTYPE_PARAM, (dvoid *)&num_elements, (ub4 *)0, OCI_ATTR_NUM_ELEMS, errh)) return OCI_ERROR; } /* now use the collection_element parameter handle to retrieve information about the collection element */ element_typecode = 0; if (OCIAttrGet((dvoid *)collection_element_parmh, OCI_DTYPE_PARAM, (dvoid *)&element_typecode, (ub4 *)0, OCI_ATTR_TYPECODE, errh)) return OCI_ERROR; /* do the same to describe additional collection element information; this is very similar to describing type attributes */ } if (dschp) OCIHandleFree((dvoid *) dschp, OCI_HTYPE_DESCRIBE); ...
The following sample code shows a loop that retrieves the column names and datatypes corresponding to a query following query execution. The query was associated with the statement handle by a prior call to OCIStmtPrepare()
.
... OCIParam *mypard = (OCIParam *) 0; ub2 dtype; text *col_name; ub4 counter, col_name_len, char_semantics; ub2 col_width; sb4 parm_status; text *sqlstmt = (text *)"SELECT * FROM employees WHERE employee_id = 100"; checkerr(errhp, OCIStmtPrepare(stmthp, errhp, (OraText *)sqlstmt, (ub4)strlen((char *)sqlstmt), (ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT)); checkerr(errhp, OCIStmtExecute(svchp, stmthp, errhp, 0, 0, (OCISnapshot *)0, (OCISnapshot *)0, OCI_DEFAULT)); /* Request a parameter descriptor for position 1 in the select-list */ counter = 1; parm_status = OCIParamGet((dvoid *)stmthp, OCI_HTYPE_STMT, errhp, (dvoid **)&mypard, (ub4) counter); /* Loop only if a descriptor was successfully retrieved for current position, starting at 1 */ while (parm_status == OCI_SUCCESS) { /* Retrieve the datatype attribute */ checkerr(errhp, OCIAttrGet((dvoid*) mypard, (ub4) OCI_DTYPE_PARAM, (dvoid*) &dtype,(ub4 *) 0, (ub4) OCI_ATTR_DATA_TYPE, (OCIError *) errhp )); /* Retrieve the column name attribute */ col_name_len = 0; checkerr(errhp, OCIAttrGet((dvoid*) mypard, (ub4) OCI_DTYPE_PARAM, (dvoid**) &col_name, (ub4 *) &col_name_len, (ub4) OCI_ATTR_NAME, (OCIError *) errhp )); /* Retrieve the length semantics for the column */ char_semantics = 0; checkerr(errhp, OCIAttrGet((dvoid*) mypard, (ub4) OCI_DTYPE_PARAM, (dvoid*) &char_semantics,(ub4 *) 0, (ub4) OCI_ATTR_CHAR_USED, (OCIError *) errhp )); col_width = 0; if (char_semantics) /* Retrieve the column width in characters */ checkerr(errhp, OCIAttrGet((dvoid*) mypard, (ub4) OCI_DTYPE_PARAM, (dvoid*) &col_width, (ub4 *) 0, (ub4) OCI_ATTR_CHAR_SIZE, (OCIError *) errhp )); else /* Retrieve the column width in bytes */ checkerr(errhp, OCIAttrGet((dvoid*) mypard, (ub4) OCI_DTYPE_PARAM, (dvoid*) &col_width,(ub4 *) 0, (ub4) OCI_ATTR_DATA_SIZE, (OCIError *) errhp )); /* increment counter and get next descriptor, if there is one */ counter++; parm_status = OCIParamGet((dvoid *)stmthp, OCI_HTYPE_STMT, errhp, (dvoid **)&mypard, (ub4) counter); } /* while */ ...