23
Sat, Nov
1 New Articles
  1. You are here:  
  2. Home
  3. Programming
  4. Programming - Other
  5. Building Python Applications That Work with Db2, Part 4

Building Python Applications That Work with Db2, Part 4

Programming - Other
Typography
  • Smaller Small Medium Big Bigger
  • Default Helvetica Segoe Georgia Times

Calling Stored Procedures. Read Part 1, Part 2, and Part 3 of this series.

Editor's Note: This article is excerpted from chapter 6 of QuickStart Guide to Db2 Development with Python, by Roger Sanders.

If an application has one or more transactions that perform a relatively large amount of work with little or no user interaction, those transactions can be encapsulated and stored on the database server as a stored procedure. Stored procedures make it possible to perform data processing operations directly at the server, which typically is a high-performant computer that can provide quick, coordinated data access. More importantly, because a stored procedure is invoked by a single SQL statement (or API/Cursor object method), fewer messages have to be transmitted across the network—only the data that is actually needed at the client has to be sent across the wire.

Once a stored procedure has been created and registered with a Db2 database (using the CREATE PROCEDURE SQL statement), that procedure can be invoked, either interactively using a utility like the Db2 CLP, or from an application. Typically, stored procedures are invoked by executing the CALL SQL statement. However, with Python applications, the preferred way to invoke a stored procedure is by executing the ibm_db.callproc() API (if the ibm_db library is used), or the .callproc() Cursor object attribute (if the ibm_db_dbi library is used).

The following pseudo-source code example illustrates how ibm_ db.callproc() API in the ibm_db Python library might be used to execute a stored procedure:

#! /usr/bin/python3

# Load The Appropriate Python Modules

import ibm_db

# Define And Initialize The Appropriate Variables

...

pVals = (0.0, 0.0)

# Construct The String That Will Be Used To Connect

# To A Database, Then Establish A Connection

...


# Define An SQL Statement To Create A

# Stored Procedure

sqlStmt = "CREATE OR REPLACE PROCEDURE salary_stats "

sqlStmt += "(OUT maxSal DOUBLE, OUT minSal DOUBLE) "

sqlStmt += "DYNAMIC RESULT SETS 0 "

sqlStmt += "BEGIN"

sqlStmt += "SELECT MAX(salary) INTO maxSal "

sqlStmt += "FROM employee; "

sqlStmt += "SELECT MIN(salary) INTO minSal "

sqlStmt += "FROM employee; "

sqlStmt += "END"

# Execute The SQL Statement Just Defined

retCode = ibm_db.exec_immediate(connID, sqlStmt)

# Execute The Stored Procedure Just Created

results = ibm_db.callproc(connID, "salary_stats", pVals)

# Display The Values Returned By The Stored Procedure

print("Highest salary : $ ", end="")

print(results[1])

print("Lowest salary: $ ", end="")

print(results[2])

...

It’s important to note that a single stored procedure is capable of returning zero, one, or more result sets, depending on how it was designed. (If you look closely at the pseudo-source code example just presented, you will see a line that reads “DYNAMIC RESULT SETS 0”; this line tells Db2 the procedure will not return any result sets.) The ibm_db.next_result() API (if the ibm_db library is used), or the .nextset() Cursor object method (if the ibm_db_dbi library is used), can be used to initialize processing of the next result set available if a stored procedure returns more than one result set.

Terminating a Db2 Server or Database Connection

The last thing every Db2-based application must do before returning control to the operating system is terminate any Db2 server or database connections that have been established. When the ibm_db Python library is used, connections can be terminated by calling the ibm_db_dbi.close() API; when the ibm_db_dbi Python library is used, connections can be terminated by executing the .close() method of the Connection object that was returned when the ibm_db_dbi.connect() API was invoked.

Obtaining Information About a Data Source and Setting Driver Options

There may be times when it is necessary to obtain information about a Db2 client, server, or database an application is connected to. For this reason, all CLI/ODBC drivers must support a set of functions that can provide information about the capabilities of a driver and the driver’s underlying data source. And, because the Db2 CLI driver serves as the foundation for the ibm_db and ibm_db_dbi libraries, similar capability is available to Python applications that use the ibm_db library. (This functionality is NOT available with the ibm_db_dbi library.)

The ibm_db.client_info() and ibm_db.server_info() APIs can be used to obtain information about a Db2 client or server being used. And, metadata from a Db2 database’s system catalog can be obtained by executing any of the following APIs:

  • tables()
  • table_privileges()
  • columns()
  • column_privileges()
  • special_columns()
  • statistics()
  • primary_keys()
  • foreign_keys()
  • procedures()
  • procedure_columns()

Most data source drivers contain additional information that can be changed to alter the way in which a driver behaves for a particular application. This updatable information is referred to as driver attributes or options. And with the ibm_db library, two types of driver options are available: connection options and SQL statement options. Python applications can retrieve the value of the connection and statement options available by executing the ibm_db.get_option() API. And, they can change the value of select connection and statement options by calling the ibm_ db.set_option() API.

Diagnostics and Error Handling

Error handling is an important part of any application, and Python applications that interact with Db2 are no exception. At a minimum, a Db2- Python application should always check to see if an API or object method that was invoked was able to execute successfully. Often, this can be done by examining the API or object method’s return code. (For the most part, APIs in the ibm_db library return False or None if they fail to execute. If an object method in the ibm_db_dbi library fails to execute, an Error or subclass exception will typically be raised.) In either case, users should be notified that an error or warning condition has occurred and, whenever possible, they should be provided with sufficient diagnostic information to help them identify and correct the problem.

Although return codes can indicate that an error or warning condition occurred, they do not always provide an application (or developer or user) with specific information about what caused the error or warning to be generated. Because additional information about an error or warning condition is usually needed to resolve a problem, Db2 (as well as other relational database products) use a set of error message codes known as SQLSTATEs to provide supplementary diagnostic information for warnings and errors. SQLSTATEs are alphanumeric strings that are five characters (bytes) in length and have the format ccsss, where cc indicates the error message class and sss indicates the error message subclass.

Any SQLSTATE that has a class of 01 corresponds to a warning; any SQLSTATE that has a class of HY corresponds to an error that was generated by the Db2 CLI; and any SQLSTATE that has a class of IM corresponds to an error that was generated by the ODBC Driver Manager. (Because different database servers often have different diagnostic message codes, SQLSTATEs follow standards that are outlined in the X/Open CLI standard specification. This standardization of SQLSTATE values enables application developers to process errors and warnings consistently across different relational database products.)

Unlike return codes, SQLSTATEs are often treated as guidelines, and drivers are not required to return them. Consequently, most applications simply display them, along with any corresponding diagnostic message and native error code available. Loss of functionality rarely occurs with this approach because applications normally do not base programming logic on SQLSTATE values.

When the ibm_db library is used, SQLSTATE values associated with Db2 server or database connections can be obtained by executing the ibm_ db.conn_error() API. On the other hand, SQLSTATE values associated with SQL statements can be retrieved by executing the ibm_db.stmt_ error() API. Developers using the ibm_db_dbi library, however, will find that a different set of error codes are used to conform to the PEP 249 — Python Database API Specification. Consequently, SQLSTATE values are not available when this library is used.

SQLSTATE values alone may not be enough to help resolve a problem if an application user is unfamiliar with them. Therefore, two additional APIs that can be used to obtain Db2-specific error messages associated with connections and SQL statements are provided with the ibm_db library. These APIs are ibm_db.conn_errormsg() and ibm_db.conn_errormsg().

For examples of how to perform error handling using API return codes, as well as the error handling APIs just discussed, refer to the sample programs found in the IBM Db2-Python GitHub repository.

Enjoy this set of excerpts?  Want more?  You can pick up Roger Sander's book, QuickStart Guide to Db2 Development with Python, at the MC Press Bookstore Today!

Roger Sanders

Roger E. Sanders is a Principal Sales Enablement & Skills Content Specialist at IBM. He has worked with Db2 (formerly DB2 for Linux, UNIX, and Windows) since it was first introduced on the IBM PC (1991) and is the author of 26 books on relational database technology (25 on Db2; one on ODBC). For 10 years he authored the “Distributed DBA” column in IBM Data Magazine, and he has written articles for publications like Certification Magazine, Database Trends and Applications, and IDUG Solutions Journal (the official magazine of the International Db2 User's Group), as well as tutorials and articles for IBM's developerWorks website. In 2019, he edited the manuscript and prepared illustrations for the book “Artificial Intelligence, Evolution and Revolution” by Steven Astorino, Mark Simmonds, and Dr. Jean-Francois Puget.

From 2008 to 2015, Roger was recognized as an IBM Champion for his contributions to the IBM Data Management community; in 2012 he was recognized as an IBM developerWorks Master Author, Level 2 (for his contributions to the IBM developerWorks community); and, in 2021 he was recognized as an IBM Redbooks Platinum Author. He lives in Fuquay Varina, North Carolina.

MC Press books written by Roger E. Sanders available now on the MC Press Bookstore.

QuickStart Guide to Db2 Development with Python QuickStart Guide to Db2 Development with Python
Discover how Python, SQL, and Db2 can successfully be used with each other.
List Price $9.95

Now On Sale

DB2 10.5 Fundamentals for LUW (Exam 615) DB2 10.5 Fundamentals for LUW (Exam 615)
Don't even think about attempting to take the DB2 Fundamentals exam without this indispensable study guide.
List Price $79.95

Now On Sale
DB2 10.1 Fundamentals (Exam 610) DB2 10.1 Fundamentals (Exam 610)
Let one of the world's leading DB2 authors and a participant in the exam development help you succeed.
List Price $79.95

Now On Sale

Artificial Intelligence: Evolution and Revolution Artificial Intelligence: Evolution and Revolution
Operational AI has become available to the masses, setting the wheels in motion for a worldwide AI revolution that has never been seen before.
List Price $16.95

Now On Sale
DB2 10.5 DBA for LUW Upgrade from DB2 10.1: Certification Study Notes DB2 10.5 DBA for LUW Upgrade from DB2 10.1: Certification Study Notes
Here's everything you need to know to take and pass Exam 311, complete with a practice exam and study key.
List Price $21.95

Now On Sale

From Idea to Print From Idea to Print
Here's everything you need to know to turn your technical knowledge and expertise into a published article or book.
List Price $49.95

Now On Sale
DB2 9 Fundamentals (Exam 730) DB2 9 Fundamentals (Exam 730)
Use this review before taking the test to prove you've mastered the basics of DB2 9.
List Price $59.95

Now On Sale

DB2 9 for Linux, UNIX, and Windows Database Administration (Exam 731) DB2 9 for Linux, UNIX, and Windows Database Administration (Exam 731)
Use this indispensable study guide to prepare to take, and pass, Exam 731.
List Price $64.95

Now On Sale
DB2 9.7 for Linux, UNIX, and Windows Database Administration (Exam 541) DB2 9.7 for Linux, UNIX, and Windows Database Administration (Exam 541)
Get ready to take the DB2 9.7 certification exam with this handy study guide.
List Price $21.95

Now On Sale

DB2 9 for Linux, UNIX, and Windows Advanced Database Administration (Exam 734) DB2 9 for Linux, UNIX, and Windows Advanced Database Administration (Exam 734)
Review all exam topics and take the included practice test to be sure you're ready on testing day.
List Price $64.95

Now On Sale
DB2 9 for Linux, UNIX, and Windows Database Administration Upgrade (Exam 736) DB2 9 for Linux, UNIX, and Windows Database Administration Upgrade (Exam 736)
Prep for success with the master of DB2 certification study guides!
List Price $34.95

Now On Sale

Data Fabric: An Intelligent Data Architecture for AI Data Fabric: An Intelligent Data Architecture for AI
This book explains the concepts and values that a data fabric approach can deliver to both technical and business communities.
List Price $19.95

Now On Sale
BLOG COMMENTS POWERED BY DISQUS

LATEST COMMENTS

Support MC Press Online

$

Book Reviews

Resource Center

  • SB Profound WC 5536 Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application. You can find Part 1 here. In Part 2 of our free Node.js Webinar Series, Brian May teaches you the different tooling options available for writing code, debugging, and using Git for version control. Brian will briefly discuss the different tools available, and demonstrate his preferred setup for Node development on IBM i or any platform. Attend this webinar to learn:

  • SB Profound WP 5539More than ever, there is a demand for IT to deliver innovation. Your IBM i has been an essential part of your business operations for years. However, your organization may struggle to maintain the current system and implement new projects. The thousands of customers we've worked with and surveyed state that expectations regarding the digital footprint and vision of the company are not aligned with the current IT environment.

  • SB HelpSystems ROBOT Generic IBM announced the E1080 servers using the latest Power10 processor in September 2021. The most powerful processor from IBM to date, Power10 is designed to handle the demands of doing business in today’s high-tech atmosphere, including running cloud applications, supporting big data, and managing AI workloads. But what does Power10 mean for your data center? In this recorded webinar, IBMers Dan Sundt and Dylan Boday join IBM Power Champion Tom Huntington for a discussion on why Power10 technology is the right strategic investment if you run IBM i, AIX, or Linux. In this action-packed hour, Tom will share trends from the IBM i and AIX user communities while Dan and Dylan dive into the tech specs for key hardware, including:

  • Magic MarkTRY the one package that solves all your document design and printing challenges on all your platforms. Produce bar code labels, electronic forms, ad hoc reports, and RFID tags – without programming! MarkMagic is the only document design and print solution that combines report writing, WYSIWYG label and forms design, and conditional printing in one integrated product. Make sure your data survives when catastrophe hits. Request your trial now!  Request Now.

  • SB HelpSystems ROBOT GenericForms of ransomware has been around for over 30 years, and with more and more organizations suffering attacks each year, it continues to endure. What has made ransomware such a durable threat and what is the best way to combat it? In order to prevent ransomware, organizations must first understand how it works.

  • SB HelpSystems ROBOT GenericIT security is a top priority for businesses around the world, but most IBM i pros don’t know where to begin—and most cybersecurity experts don’t know IBM i. In this session, Robin Tatam explores the business impact of lax IBM i security, the top vulnerabilities putting IBM i at risk, and the steps you can take to protect your organization. If you’re looking to avoid unexpected downtime or corrupted data, you don’t want to miss this session.

  • SB HelpSystems ROBOT GenericCan you trust all of your users all of the time? A typical end user receives 16 malicious emails each month, but only 17 percent of these phishing campaigns are reported to IT. Once an attack is underway, most organizations won’t discover the breach until six months later. A staggering amount of damage can occur in that time. Despite these risks, 93 percent of organizations are leaving their IBM i systems vulnerable to cybercrime. In this on-demand webinar, IBM i security experts Robin Tatam and Sandi Moore will reveal:

  • FORTRA Disaster protection is vital to every business. Yet, it often consists of patched together procedures that are prone to error. From automatic backups to data encryption to media management, Robot automates the routine (yet often complex) tasks of iSeries backup and recovery, saving you time and money and making the process safer and more reliable. Automate your backups with the Robot Backup and Recovery Solution. Key features include:

  • FORTRAManaging messages on your IBM i can be more than a full-time job if you have to do it manually. Messages need a response and resources must be monitored—often over multiple systems and across platforms. How can you be sure you won’t miss important system events? Automate your message center with the Robot Message Management Solution. Key features include:

  • FORTRAThe thought of printing, distributing, and storing iSeries reports manually may reduce you to tears. Paper and labor costs associated with report generation can spiral out of control. Mountains of paper threaten to swamp your files. Robot automates report bursting, distribution, bundling, and archiving, and offers secure, selective online report viewing. Manage your reports with the Robot Report Management Solution. Key features include:

  • FORTRAFor over 30 years, Robot has been a leader in systems management for IBM i. With batch job creation and scheduling at its core, the Robot Job Scheduling Solution reduces the opportunity for human error and helps you maintain service levels, automating even the biggest, most complex runbooks. Manage your job schedule with the Robot Job Scheduling Solution. Key features include:

  • LANSA Business users want new applications now. Market and regulatory pressures require faster application updates and delivery into production. Your IBM i developers may be approaching retirement, and you see no sure way to fill their positions with experienced developers. In addition, you may be caught between maintaining your existing applications and the uncertainty of moving to something new.

  • LANSAWhen it comes to creating your business applications, there are hundreds of coding platforms and programming languages to choose from. These options range from very complex traditional programming languages to Low-Code platforms where sometimes no traditional coding experience is needed. Download our whitepaper, The Power of Writing Code in a Low-Code Solution, and:

  • LANSASupply Chain is becoming increasingly complex and unpredictable. From raw materials for manufacturing to food supply chains, the journey from source to production to delivery to consumers is marred with inefficiencies, manual processes, shortages, recalls, counterfeits, and scandals. In this webinar, we discuss how:

  • The MC Resource Centers bring you the widest selection of white papers, trial software, and on-demand webcasts for you to choose from. >> Review the list of White Papers, Trial Software or On-Demand Webcast at the MC Press Resource Center. >> Add the items to yru Cart and complet he checkout process and submit

  • Profound Logic Have you been wondering about Node.js? Our free Node.js Webinar Series takes you from total beginner to creating a fully-functional IBM i Node.js business application.

  • SB Profound WC 5536Join us for this hour-long webcast that will explore:

  • Fortra IT managers hoping to find new IBM i talent are discovering that the pool of experienced RPG programmers and operators or administrators with intimate knowledge of the operating system and the applications that run on it is small. This begs the question: How will you manage the platform that supports such a big part of your business? This guide offers strategies and software suggestions to help you plan IT staffing and resources and smooth the transition after your AS/400 talent retires. Read on to learn: