17 Developing Applications for Windows

About Java Enhancements

Oracle Database includes an integrated Java Virtual Machine and JIT Compiler. Oracle Database also provides Oracle Java Database Connectivity (JDBC) Drivers. For more information, refer to Oracle Database Java Developer's Guide and Oracle Database JDBC Developer's Guide.

About ODP.NET

Oracle Data Provider for .NET (ODP.NET) is an implementation of a Microsoft ADO.NET data provider for Oracle Database. ODP.NET uses Oracle native APIs to offer fast and reliable access to Oracle data and features from any .NET application. ODP.NET also uses and inherits classes and interfaces available in the Microsoft .NET Framework Class Library. For more information, refer to Oracle Data Provider for .NET Developer's Guide for Microsoft Windows and My Oracle Support Note 726240.1.

About Oracle Developer Tools for Visual Studio

The Oracle Developer Tools for Visual Studio (ODT) is a tightly integrated "Add-in" for Microsoft Visual Studio. ODT integrates with Visual Studio to make it easy to browse and edit Oracle schema objects using integrated visual designers and can automatically generate .NET code through a simple drag and drop. Developers can modify table data, execute Oracle SQL statements, edit and debug PL/SQL code, generate and edit SQL scripts, and develop and deploy .NET stored procedures. There are many more features included with these tools. For more information, visit the ODT web home at

http://www.oracle.com/technetwork/developer-tools/visual-studio/overview/index.html

About Oracle Providers for ASP.NET

Starting with .NET Framework 2.0, ASP.NET includes service providers that store state in databases. By storing this state in a database, applications can ensure high availability of data, while making the data equally available to all web servers. For more information, refer to Oracle Providers for ASP.NET Developer's Guide for Microsoft Windows.

About XML Support

Oracle XML products include XML Developer's Kit (XDK) and Oracle XML SQL Utility. For more information, refer to:

• Oracle XML Developer's Kit Programmer's Guide

• Oracle XML DB Developer's Guide

• Oracle Database XML Java API Reference

• Oracle Database XML C API Reference

• Oracle Database XML C++ API Reference

• Oracle Database SQL Language Reference

• Oracle Database PL/SQL Packages and Types Reference

About Support for Internet Applications

Oracle Database support for internet applications includes Oracle WebCenter Portal, which enables you to publish your data to the web, Oracle Web Tier (Oracle HTTP Server), and PL/SQL Embedded Gateway, which offers PL/SQL procedures stored in Oracle Database that can be started through browsers. For more information, refer to:

• Oracle Fusion Middleware Installation Guide for Oracle WebCenter Portal

• Oracle Fusion Middleware Tutorial for Oracle WebCenter Portal Developers

• Oracle Enterprise Manager Grid Control Installation and Basic Configuration

  Oracle Database provides built-in mechanisms that address the requirements of the largest PHP, Ruby, Python Web, and Rich Internet Applications. The features include extreme connectivity, scalability, caching, nonintrusive performance acceleration, advanced security, and high-availability.

About Oracle Services for Microsoft Transaction Server

With Oracle Services for Microsoft Transaction Server, Oracle Database can be a resource manager in Microsoft Distributed Transaction Coordinator (DTC) transactions. Oracle Services for Microsoft Transaction Server act as a proxy for Oracle Database to the DTC. For more information, refer to Oracle Services for Microsoft Transaction Server Developer's Guide for Microsoft Windows.

About Oracle Provider for OLE DB

Refer to Oracle Provider for OLE DB Developer's Guide for Microsoft Windows for information on OLE DB.

About Oracle ODBC Driver

Open Database Connectivity (ODBC) provides a common C programming interface for applications to access data from database management systems. Access to databases is managed by the ODBC Driver Manager. The driver manager provides the linkage between an ODBC application and an ODBC driver for a specific database management system.

Oracle ODBC Driver provides access to Oracle databases for applications written using the ODBC interface.

Oracle Technology Network has both Oracle home based ODBC driver and Instant Client enabled ODBC driver.

Download Instant Client enabled ODBC driver from

http://www.oracle.com/technetwork/database/features/instant-client/index.html

About Pro*C/C++ and Pro*COBOL Applications

Refer to the following guides for more information on Pro*C/C++ and Pro*COBOL applications:

• Pro*C/C++ Programmer's Guide

• Pro*COBOL Programmer's Guide

• Oracle Call Interface Programmer's Guide

External Procedures Overview

External procedures are functions written in a third-generation language (C, for example) and callable from within PL/SQL or SQL as if they were a PL/SQL routine or function. External procedures let you take advantage of strengths and capabilities of a third-generation programming language in a PL/SQL environment.

The main advantages of external procedures are:

• Performance, because some tasks are performed more efficiently in a third-generation language than in PL/SQL, which is better suited for SQL transaction processing

• Code re-usability, because dynamic link libraries (DLLs) can be called directly from PL/SQL programs on the server or in client tools

You can use external procedures to perform specific processes:

• Solving scientific and engineering problems

• Analyzing data

• Controlling real-time devices and processes

To create and use an external procedure, perform the following sequential steps:

• Installing and Configuring Oracle Database and Oracle Net Services

• Writing an External Procedure

• Building a DLL

• Registering an External Procedure

• Restricting Library-Related Privileges to Trusted Users Only

• Executing an External Procedure

  Note:

  • You must have a C compiler and linker installed on your system to build DLLs.

  • You can combine the instructions described in the fourth and fifth tasks into one SQL script that automates the task of registering and executing your external procedure. See ORACLE_HOME\rdbms\extproc\extern.sql for an example of a SQL script that combines these steps.

Installing and Configuring Oracle Database and Oracle Net Services

This section describes installation and configuration of Oracle Database and Oracle Net.

Writing an External Procedure

Using a third-generation programming language, you can write functions to be built into DLLs and started by EXTPROC. The following is a simple Microsoft Visual C++ example of an external procedure called FIND_MAX:

#include <windows.h>
#define NullValue -1
/*
  This function tests if x is at least as big as y.
*/
long __declspec(dllexport) find_max(long   x, 
                                short   x_indicator, 
long    y, 
short y_indicator, 
                                short *ret_indicator)
{
   /* It can be tricky to debug DLL's that are being called by a process
      that is spawned only when needed, as in this case.  
      Therefore try using the DebugBreak(); command.  
      This will start your debugger.  Uncomment the line with DebugBreak(); 
      in it and you can step right into your code.
   */
   /* DebugBreak();  */

   /* First check to see if you have any nulls. */
   /* Just return a null if either x or y is null. */

   if ( x_indicator==NullValue || y_indicator==NullValue) {
      *ret_indicator = NullValue;   
      return(0);
   } else { 
      *ret_indicator = 0;       /* Signify that return value is not null. */
      if (x >= y) return x;
      else return y;
   }
}

Building a DLL

After writing your external procedures in a third-generation programming language, use the appropriate compiler and linker to build a DLL, making sure to export the external procedures as noted previously. See your compiler and linker documentation for instructions on building a DLL and exporting its functions.

You can build the external procedure FIND_MAX, created in "Writing an External Procedure", into a DLL called extern.dll by going to ORACLE_HOME\rdbms\extproc and typing make. After building the DLL, you can move it to any directory on your system.

The default behavior of EXTPROC is to load DLLs only from ORACLE_HOME\bin or ORACLE_HOME\lib. To load DLLs from other directories, you must set environment variable EXTPROC_DLLS to a colon (:) separated list (semicolon-separated on Windows systems) of DLL names qualified with their complete paths. The preferred way to set this environment variable is through the ENVS parameter in listener.ora.

Registering an External Procedure

Once you have built a DLL containing your external procedures, you must register your external procedures with Oracle Database. Starting with Oracle Database 12c Release 1 (12.1), you can configure the EXTPROC process to be authenticated through a CREDENTIAL for better security.

Oracle Database 12c Release 1 (12.1) supports two new extensions to the CREATE LIBRARY command. This includes a CREDENTIAL clause and a DIRECTORY object option. The CREDENTIAL clause defines the user the EXTPROC runs as while the DIRECTORY object option specifies the directory where the DLL can be located.

To create a PL/SQL library to map to the DLL:

1. Set environment variable EXTPROC_DLLS in the ENVS parameter in listener.ora. For example:

   SID_LIST_LISTENER =
    (SID_LIST =
     (SID_DESC =
      (SID_NAME=PLSExtProc)
      (ENVS=EXTPROC_DLLS=C:\app\oracle\product\12.1.0\dbhome_1\rdbms\extproc\extern.dll)
      (ORACLE_HOME=C:\app\oracle\product\12.1.0\dbhome_1)
      (PROGRAM=extproc)
     )
    )
   

2. Start SQL*Plus:

   C:\> sqlplus
   

3. Connect to the database with appropriate username and password.

4. Create the PL/SQL library using the CREATE LIBRARY command:

   DBMS_CREDENTIAL.CREATE_CREDENTIAL(...);
   CREATE DIRECTORY DLL_LOC as ...;
   CREATE LIBRARY externProcedures as 'extern.dll' in DLL_LOC credential the_credential;
   

   where the_credential is the name chosen during the DBMS_CREDENTIAL.CREATE_CREDENTIAL invocation

   SQL> CREATE LIBRARY externProcedures AS 'C:\app\oracle\product\12.1.0\dbhome_1\rdbms\ extproc\extern.dll';
   

   where externProcedures is an alias library (essentially a schema object in the database), and

   C:\app\oracle\product\12.1.0\dbhome_1\rdbms\extproc\extern.dll
   

   is the path to the Windows operating system dllextern.dll. This example uses C:\app\oracle\product\12.1.0 as your Oracle base and dbhome_1 as your Oracle home.

   Note:

   The DBA must grant the EXECUTE privilege on the PL/SQL library to users who want to call the library's external procedure from PL/SQL or SQL. Separate EXECUTE privilege on credential and directory object extensions are required for them to function properly.

5. Create a PL/SQL program unit specification.

   Do this by writing a PL/SQL subprogram that uses the EXTERNAL clause instead of declarations and a BEGIN...END block. The EXTERNAL clause is the interface between PL/SQL and the external procedure. The EXTERNAL clause identifies the following information about the external procedure:

   • Name

   • DLL alias

   • Programming language in which it was written

   • Calling standard (defaults to C if omitted)

   In the following example, externProcedures is a DLL alias. You need the EXECUTE privilege for this library. The external procedure to call is find_max. If enclosed in double quotation marks, it becomes case-sensitive. The LANGUAGE term specifies the language in which the external procedure was written.

   CREATE OR REPLACE FUNCTION PLS_MAX(
     x BINARY_INTEGER,
     y BINARY_INTEGER)
   RETURN BINARY_INTEGER AS EXTERNAL
     LIBRARY externProcedures
     NAME "find_max"
     LANGUAGE C
     PARAMETERS (
       x long,                  -- stores value of x
       x_INDICATOR short,       -- used to determine if x is a NULL value
       y long,                  -- stores value of y
       y_INDICATOR short,        -- used to determine if y is a NULL value
     RETURN INDICATOR short );  -- need to pass pointer to return value's
                                -- indicator variable to determine if NULL
   -- This means that my function will be defined as:
       -- long max(long x, short x_indicator,
       -- long y, short y_indicator, short * ret_indicator)
   

Restricting Library-Related Privileges to Trusted Users Only

The CREATE LIBRARY, CREATE ANY LIBRARY, ALTER ANY LIBRARY, and EXECUTE ANY LIBRARY privileges, and grants of EXECUTE ON library_name convey a great deal of power to users. If you plan to create PL/SQL interfaces to libraries, only grant the EXECUTE privilege to the PL/SQL interface. Do not grant EXECUTE on the underlying library. You must have the EXECUTE privilege on a library to create the PL/SQL interface to it. However, users have this privilege implicitly on libraries that they create in their own schemas. Explicit grants of EXECUTE ON library_name are rarely required. Only make an explicit grant of these privileges to trusted users, and never to the PUBLIC role.

Executing an External Procedure

To run an external procedure, you must call the PL/SQL program unit (that is, the alias for the external function) that registered the external procedure. These calls can appear in any of the following:

• Anonymous blocks

• Standalone and packaged subprograms

• Methods of an object type

• Database triggers

• SQL statements (calls to packaged functions only)

In "Registering an External Procedure", PL/SQL function PLS_MAX registered external procedure find_max. Follow these steps to run find_max:

1. Call PL/SQL function PLS_MAX from a PL/SQL routine named UseIt:

   SET SERVER OUTPUT ON
   CREATE OR REPLACE PROCEDURE UseIt AS
                   a integer;
                   b integer;
                   c integer;
   BEGIN
                   a := 1;
                   b := 2;
                   c := PLS_MAX(a,b);
                   dbms_output.put_line('The maximum of '||a||' and '||b||' is  '||c);
   END;
   

2. Run the routine:

   SQL> EXECUTE UseIt;
   

Using Package DEBUG_EXTPROC

To help you debug external procedures, PL/SQL provides utility package DEBUG_EXTPROC. To install the package, run script dbgextp.sql, which you can find in the PL/SQL demo directory.

To use the package, follow instructions in dbgextp.sql. Your Oracle Database account must have EXECUTE privileges on the package and CREATE LIBRARY privileges.

To debug external procedures:

1. From Windows Task Manager, in the Processes dialog, select ExtProc.exe.

2. Right click, and select Debug.

3. Click OK in the message window.

   If you have built your DLL in a debug fashion with Microsoft Visual C++, then Visual C++ is activated.

4. In the Visual C++ window, select Edit > Breakpoints.

   Use the breakpoint identified in dbgextp.sql in the PL/SQL demo directory.

   See Also:

   • ORACLE_HOME\rdbms\extproc\readme.doc (explains how to run the sample and provides debugging advice)

   • Oracle Database PL/SQL Language Reference

   • Oracle Database Java Developer's Guide

   • "Calling External Procedures" in Oracle Database Development Guide

   • Oracle Database Data Cartridge Developer's Guide