Chapter 14_Logical Locking

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Logical Locking | 6.14 March-2005 © 2005 IBM Corporation

Logical Locking

IBM Global Services

© 2005 IBM Corporation2 March-2005Logical Locking | 6.14

Objectives

The participants will be able to: Lock database records.

Create a lock object.

Recognize the automatic creation of the ENQUEUE and DEQUEUE function modules.

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Overview

Academy Awards

Year

Category

1994

PIC

Winner Forrest Gump

Notes Great movie !!!

Critic Ellen

UpdateExit

Enter Name

Academy Awards

Year

Category

1994

PIC

Winner Forrest Gump

Notes What about Pulp Fiction?!?

Critic Mark

UpdateExit

Enter Name

Currently, multiple users can edit

the same record at the same time. We will learn how to prevent this occurrence.

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Locking Database Records

Database Lock

DatabaseTable

ABAPProgram

Logical Lock

In an ABAP program, logical locking ensures that only one user can edit a record at any one time.

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Lock Objects

ABAP DictionaryABAP DictionaryABAP DictionaryABAP Dictionary

PrimaryTable

LockArguments

YMOVIEAAYEAR

CATEGORY

To use SAP’s logical locking mechanism, you need to define a lock object.

A lock object is an ABAP Dictionary object.

LockObject

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Lock Objects (Contd.)

ABAP DictionaryABAP DictionaryABAP DictionaryABAP Dictionary

Primary

Table

Lock

Arguments

YMOVIEAAYEAR

CATEGORY

To use SAP’s logical locking mechanism, you need to define a lock object.

A lock object is an ABAP Dictionary object.

LockObject

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Function Modules

CALL FUNCTION ‘ENQUEUE_EZ_YMOVIE’

EXPORTING

AAYEAR = YMOVIE-AAYEAR

CATEGORY = YMOVIE-CATEGORY

EXCEPTIONS

FOREIGN_LOCK = 1

SYSTEM_FAILURE = 2

OTHERS = 3.

IF SY-SUBRC = 1.

MESSAGE E004.

ENDIF.

CALL FUNCTION ‘DEQUEUE_EZ_YMOVIE’

EXPORTING

AAYEAR = YMOVIE-AAYEAR

CATEGORY = YMOVIE-CATEGORY

EXCEPTIONS

OTHERS = 1.

If a “lock” exists for the record, the

“DEQUEUE” function module will

remove the “lock” on the record.

If a “lock” already exists for the record, the “ENQUEUE” function

Module will raise the “foreign lock” exception. If a “lock” does

not exist, this function module will “lock” the record.

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Locking and Unlocking

MODULE SELECT_LISTING INPUT.

IF OKCODE = ‘EDIT’.

PERFORM LOCK.

* code to select record from YMOVIE

ENDIF.

ENDMODULE.

MODULE UPDATE INPUT.

IF OKCODE = ‘UPDA’.

UPDATE YMOVIE.

* code to commit or rollback

PERFORM UNLOCK.

ENDIF.

ENDMODULE.

This subroutine will “call” the function

module “ENQUEUE_EZ_YMOVIE” to

check if the record is already “locked”

or to “lock” the record.

This subroutine will “call” the function

module “DEQUEUE_EZ_YMOVIE”

to “unlock” the record.

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Demonstration

Using lock objects for locking and unlocking data before and after database updates.

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Practice

Using lock objects for locking and unlocking data before and after database updates.

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Summary

Database locks on records are automatically created by the system. The system releases a database lock at every database commit (i.e., at every screen change).

Records are automatically “unlocked” at every screen change, we cannot rely on database locks to prevent multiple users from editing the same record at the same time in a multi-screen transaction.We can handle this problem with logical locks.

To use SAP’s logical locking mechanism, you need to define a lock object. When you activate a lock object, the system automatically generates two function modules: “ENQUEUE_<lock object name>” and “DEQUEUE_<lock object name>” .

It is important to understand that logical locks do not create locks at the database level. Logical locks are maintained through entries in a lock table.

Transaction “SM12” will display the current entries in the lock table.

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Questions

** MZA09I01 - PAI Modules **

MODULE END INPUT.

LEAVE TO SCREEN 0.

ENDMODULE. PROCESS AFTER INPUT.

MODULE END.

Screen 9002

PROCESS AFTER INPUT.

MODULE END AT EXIT-COMMAND.

Screen 9000

PROCESS AFTER INPUT.

MODULE END AT EXIT-COMMAND.

Screen 9001

What additional code is

needed in the module “END”?

Chapter 14_Logical Locking

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