basis dbms: triggers and stored procedures

BASIS DBMS:Triggers and Stored Procedures

Dr. Kevin King, CIONick Decker, Engineering Supervisor

BASIS International Ltd.

Overview

► Triggers• Automatically run code when reading or writing

• Configurable to run before, instead, or after

► Stored Procedures• Consolidated business and data logic

• Facilitates TP access while maintaining DB integrity

• Store data logic in DB instead of application

• Simplified Web service (RPC)

BASIS DBMS – Triggers

► Trigger Overview• A trigger is a BBj program that automatically executes in response to access to

a file

• Triggers are available for three types of file access Reads Writes Removes

• Triggers fire regardless of the file access method since they are implemented at the filesystem level READ RECORD SQL Select RecordSets

► Trigger Overview• Three types of triggers

Before ♦ “ before read,” “ before write,” “ before remove” ♦ Executes before the read takes place

After ♦ “ after read,” “ after write,” “ after remove” ♦ Executes after the read takes place

► Trigger Overview• Three types of triggers (continued)

Instead Of♦ Takes the place of, rather than supplements, the

normal file activity♦ Is mutually exclusive of a Before/After trigger♦ Will not perform the actual Read/Write/Remove – it is

up to the trigger code to do whatever action is appropriate

► Trigger Overview• Triggers are file-based

Triggers are tied to specific tables and actions Each file can have its own set of triggers Triggers can be ‘shared’

♦ Multiple triggers can reference the same program♦ Trigger programs can CALL other programs

► Trigger Overview• Triggers are managed from the Enterprise Manager

Separate mounted directories for organization Assign programs to run for each of the nine

triggers per file Enable/Disable triggers

♦ Per file♦ Per trigger

Preview trigger code

► Trigger Overview• Triggers have two components

Trigger definition file♦ XML definition file♦ Located in the same directory as the file that the trigger

definition file defines♦ Maintained automatically by the EM♦ Contains a reference to the BBj program for each type of

trigger

BBj source program that runs when the trigger fires

► Trigger Overview• Data file, trigger definition file, and BBj program may

all be stored in the same directory Easier to maintain Easier to deploy

• Trigger definition file may optionally reference BBj programs in other directories

• BBj programs may be SAVEP’d for added security

► Trigger Uses• Log access to a file

Audit trail logging all reads/writes/removes

► Trigger Uses• Restrict access to data

Only allow particular users to read♦ Tables♦ Records♦ Fields in a record

► Trigger Uses• React to an event

Keep a third party database in synch by inserting/updating/removing records at the same time instead of doing lengthy bulk copies

♦ Takes much less time♦ Only updates the records that have changed

Do not have to constantly poll to see if the data has changed

► Trigger Uses• Enforce database integrity

Validate data against related tables before inserting into the table

Ensure related tables stay in synch with one another♦ When removing a record from the OrderHeader table, use a

trigger to remove all OrderLine entries for that order number♦ When removing the last OrderLine, use a trigger to remove

the corresponding order number in the OrderHeader table

► Trigger Uses• Manipulate data without changing the application

Modify the data in an After Read trigger, so the client application will receive a modified record rather than what was in the file

Modify the data in a Before Write trigger, so the updated record is written to the file

♦ Normalize data♦ Unpack or convert dates♦ Encrypt fields

► Trigger Uses• “Instead Of” triggers accomplish different goals

Write data to a different backend database or file Flag a record as inactive or move it to a backup

table instead of processing the remove

► Trigger UsesExample: Flag a record as inactive or move it to a backup table

instead of processing the remove

chan = unt

key$ = "000001"

open(chan)"CUSTOMER"

remove(chan,key=key$)

print "Removed Cust_Num: ", key$

close(chan)

► Trigger Uses• BBj programs provide maximum flexibility

CALL existing libraries of code Launch external applications

♦ Send an e-mail when a file changes♦ Log transaction

Execute Java code

► Trigger Overhead• Everything occurs at the filesystem level

Trigger checks are fast with little overhead Triggers validated when connection made to the file

♦ An OPEN() does not succeed unless all active defined triggers are available

Trigger interpreters cached to minimize overhead

• Active triggers incur some overhead Complexity of code Quantity of code

► Trigger Notes• Error trapping is imperative

Similar to BACKGROUND programs, I/O is not available and not desired for deployment

Errors may be written to a log

• Recursion possible If a Before Read trigger causes another read on

the same table, it can get into an infinite loop

► Trigger Notes• Debugging is more challenging

I/O and error reporting is limited to logging in a deployment paradigm

MSGBOXes can be used for limited interaction during debugging sessions

Triggers can create complex interdependencies between multiple programs and tables

► Trigger Notes• Debugging is more challenging (continued)

Unanticipated and unexpected behavior may occur when using triggers that interact with one another

Untrapped errors in the trigger are passed on to the event that caused the trigger to fire

♦ If the trigger code dies with an untrapped !ERROR=12 on an OPEN(), the corresponding READ RECORD in the client application will result in a very unusual !ERROR=12

BASIS DBMS – Stored Procedures

► Stored Procedure Overview• Associated with a database

• Provides an API mechanism SQL compliant applications can interface with the

Stored Procedures Applications interact with the Stored Procedure

rather than connecting directly to the underlying tables in the database

► Stored Procedure Overview• Often referred to as SPROC, pronounced “sprock” like rock or

“ess-prock” for those ‘in the know’ (or those tired of saying Stored Procedure)

• Many DBMSs implement SPROCs as a way to provide advanced language capabilities beyond traditional SQL Control flow

IF/THEN/ELSE, SWITCH/SWEND Looping structures

FOR/NEXT, WHILE/WEND Advanced error handling

► Stored Procedure Overview• As with Triggers, SPROCs are really BBj programs designed

for a special purpose Benefits of using BBj Programs include

♦ Use existing programs♦ Call other BBj programs♦ Extremely powerful and flexible syntax

- Entire language is available- User-defined functions- SCALLs- Java code- SQL

► Stored Procedure Overview• Benefits (continued)

Easy to integrate into existing systems♦ Easy to write and maintain♦ SAVEP SPROCs for added security

Third party applications have standardized access to BBj code, functions, libraries, etc.

♦ SPROC is similar to a public function available to any SQL capable application

► Stored Procedure Overview• SPROCs - database-centric

Defined on a per database level in the Enterprise Manager

Definition and specification defined in the Data Dictionary

Applications interface with SPROCs via SQL

► Stored Procedure Overview• SPROCs have two components

SPROC definition♦ Stored in the Data Dictionary♦ Maintained from the Enterprise Manager

BBj program♦ Located anywhere♦ Interact with other programs

► Stored Procedure Overview• SPROCs similar to Triggers, but different

Explicitly called, whereas a trigger occurs automatically in response to an event

Not specific to any one table♦ Defined on a database level rather than a file-level

SQL-specific♦ Available to all SQL-capable languages and applications

- BBj, VPRO/5- C++, Perl, Visual Basic- ODBC/JDBC- Microsoft Office, OpenOffice.org

► Stored Procedure Overview• Stored Procedure Benefits

Keep business logic in one place instead of inside each client application

♦ Easier to maintain♦ Efficient reuse of existing code and libraries♦ Lower development costs♦ Easier integration with new or third party applications

- Business logic does not have to be added to applications, regardless of whether they are existing BASIS programs or third party applications

♦ Improved application reliability- Business logic separated from the application

► Stored Procedure Overview• Stored Procedure Benefits (continued)

Performance increases for third party applications♦ Processing of the data performed server-side by BBj ♦ Only pertinent results sent back ‘over the wire’ to the client

application- Application does not have to request all of the data, sift

through it, and figure out what is pertinent- Application does not have to make multiple requests

back to the server to get/set information in other tables

► Stored Procedure Specifics• Return value allows the SPROC to send a single

piece of information to the client application Optional Only one available Typically used as a status code

♦ Return success/failure of the SPROC

► Stored Procedure Specifics• Return Value (continued)

Can be of any SQL type♦ CHAR♦ VARCHAR♦ LONGVARCHAR♦ INTEGER♦ NUMERIC♦ DATE♦ TIMESTAMP♦ TIME

► Stored Procedure Specifics• Parameters offer a mechanism for the client application and

the SPROC to share data Gives flexible way to use a single SPROC for many

different scenarios♦ Application could provide filtering information for queries♦ Application could provide different instructions, so the

SPROC will operate on different tables

Makes SPROCs more efficient♦ The same SPROC can run multiple tasks, dependant on the

input from the client application

► Stored Procedure Specifics• Parameters (continued)

Parameters are optional♦ An SPROC may have no parameters

- Example: An SPROC that is designed to synchronize tables which only has a return value

♦ An SPROC may have several parameters- Flexible interaction with the client application

Parameters can be of any SQL type:♦ CHAR♦ VARCHAR♦ LONGVARCHAR♦ INTEGER♦ NUMERIC♦ DATE♦ TIMESTAMP♦ TIME

Parameters are directional♦ IN

- Applications sends data into the SPROC via a parameter♦ OUT

- SPROC sends data back to the application via a parameter

♦ IN/OUT- Application sends data to the SPROC and the SPROC

sends data back to the application via a parameter

► Stored Procedure Specifics• Result Sets allow SPROCs to return a table or set of

data to the client application Similar to the client executing a SELECT, except

that the SPROC is in charge of determining the structure of the result set

Client application executes the SPROC instead of the usual SELECT, so the SPROC’s code and underlying logic is transparent to the application

► Stored Procedure Specifics• Result Sets (continued)

Available to any application capable of executing an SQL SELECT query

♦ BBj programs♦ Visual PRO/5 and PRO/5 programs♦ BBj RecordSets♦ C++, Perl, Visual Basic♦ Microsoft Databound controls♦ Microsoft Excel, OpenOffice.org♦ Etc.

► Stored Procedure Specifics• Update Count allows an SPROC to return the

number of rows affected Similar to how an SQL UPDATE or INSERT

returns an update count The SPROC is responsible for setting this value,

so it may customize it according to the type of work for which the SPROC is responsible

► Stored Procedure Uses• Encapsulate a set of operations or queries for a

database SPROCs control access and provide a front-end

for operations on an Employee database♦ Hire (add new employees)♦ Fire (remove employees)♦ Promote (update employee information)

SPROCs can call other related SPROCs

► Stored Procedure Uses• Simpler ‘Web service’

Disparate clients can pass data into a BBj SPROC SPROC processes the information, applies

business logic, gets/sets information from other tables and sources

SPROC returns data back to the client

► Stored Procedure Uses• ‘Beef up’ traditional SQL

Client uses SQL which is relatively limited♦ Lacks control flow♦ Lacks looping structures♦ Etc.

BBj SRPOC is BBj code, so it can do whatever is necessary to provide the desired results to the client application

► Stored Procedure Uses• Simplify database interaction

Call an SPROC to add or update a customer♦ The SPROC will be responsible for finding out if the

customer exists or not, so the application’s responsibility is decreased- The SPROC checks to see if the customer exists- If the customer does exist, it executes an UPDATE- If the customer does not exist, it executes an

INSERT

► Stored Procedure Uses• Simplify database interaction (continued)

Presents a ‘souped up’ View to♦ Normalize data♦ Format data♦ Collate data from multiple tables

Delivers more power and flexibility than a View, since the SPROC can be parameterized to

♦ Limit result sets♦ Filter out undesired data♦ Customize the queries

► Stored Procedure Uses• Simplify database interaction (continued)

Utilizes recursion to solve hierarchy difficulties♦ Example: Find out how many employees are overseen

by a particular manager- Application calls the SPROC passing the manager

as a parameter- SPROC queries and totals up employees for that

manager- SPROC calls itself for each employee, and so on..- SPROC returns the total count of employees

overseen by the particular manager, including not only all of his/her subordinates, but also those employees overseen by his/her subordinates

Summary

► Triggers• Automatically run code when reading or writing

• Configurable to run before, instead, or after

► Stored Procedures• Consolidated business and data logic

• Facilitates TP access while maintaining DB integrity

• Store data logic in DB instead of Application

• Simplified Web service (RPC)

basis dbms: triggers and stored procedures

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