All the relational databases supported by DBSP have their own methods to follow predefined rules and enforce the integrity of the database. Some of these rules are established as integrity constraints in the metadata of the database (DDL). Others are raised inside stored procedures, triggers, etc.

Regarding what kind of exceptions the database are raising, is a need to present to the user a clear explanation of what is happening inside the system and why he or she is violating these rules. This could be done using the TRY-ONERROR tags.

Try - OnError Tags

These tags works like any of the try-catch blocks found on all the recent high level programming languages. The structure is very simple:

When an exception is raised inside the TRY-ONERROR block, the block delimited by the ONERROR - /TRY is executed. This block could be used for handling the exception and present an explanation to the user or redirect to another page that contains all these explanations.

Note: If an exception is raised and is not explicitly handled within a TRY-ONERROR block, then DBSP takes one of the following actions:

If the DEBUGMODE parameter in the file DBSP.ini is turned on (TRUE), a template file containing detailed explanation is displayed. This template (debugerror.dbsp) is located in the bin\Templates directory inside the installation directory.

If the DEBUGMODE parameter is turned off (FALSE), the production error template (productionerror.dbsp) is displayed instead.

Examples

Example 1. Managing check constraints exceptions

Source code

File: examples/CheckConst.dbsp

Exception handling: Check constraints                                                          <#DATASET ALIAS="OPEX" QUERYID="1">                                                                     <#/DATASET>      Job ID Description Min Salary Max Salary <#JOBID/> <#DESCRIPTION/> <#MINSALARY FORMAT="MONEY:8:2"/> <#MAXSALARY FORMAT="MONEY:8:2"/>                This table has two restrictions: MINSALARY and MAXSALARY can not be negative; MINSALARY must be lower than MAXSALARY. Try to violate this check constraints and see what happens and how the exceptions are handled.      Add a new row to the table:                                                                                                            Job ID Description Min Salary MaxSalary      Add row            SQL Sentence: ID=1 SELECT * FROM JOBS File: examples/CheckConstVal.dbsp         <#TRY>        <#QRYEXEC ALIAS="OPEX" QUERYID="2" NOW/>       <#REDIRECT DOC="checkconst.dbsp"/>     <#ONERROR>       <#SETCOOKIE NAME="CONSTRAINT" EXPRESSION="ERROR_MSG" PATTERN='Database exception: *"INTEG_*"*' PATTERNINDEX=2/>       <#IF EXPRESSION="CONSTRAINT=UNDEF">           <#SETCOOKIE NAME="CONSTRAINT" EXPRESSION="ERROR_MSG" PATTERN='Database exception: *INTEG_* *' PATTERNINDEX=2/>       <#/IF>       <#CASE>              <#OPTION EXPRESSION="CONSTRAINT=26"/>           A Job with identified as <#JOBID/> already exists.           <#OPTION EXPRESSION="CONSTRAINT=30"/>           The miminum salary must be greater that the maximum salary.           <#OPTION EXPRESSION="CONSTRAINT=28"/>           The miminum salary must greater than 0!.           <#OPTION EXPRESSION="CONSTRAINT=29"/>           The maximum salary must greater than 0!.           <#ELSE/>           Unhandled exception: <#ERROR_MSG/>       <#/CASE>            <#/TRY>    SQL Sentence: ID=2 INSERT INTO JOBS VALUES (:JOBID,:JOBDESC,:MINSAL,:MAXSAL) Test example Previous | Next