Time constraints

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USoft Production has an application timer that allows scheduled constraint execution. The timer consists of an application table T_APP_TIME, and an executable USCLOCK.EXE that updates T_APP_TIME with the current database time at regular intervals.


You can use a time constraint for future changes of customer addresses. Suppose, customers can announce a new address and the date from which the new address takes effect. The application must automatically replace the old address with the new address at the right time.

This data is stored in a separate NEW_ADDRESS table.

When the date arrives, the automatic update of the only record in the T_APP_TIME table causes the evaluation of a corrective SET_NEW_ADDRESS constraint that updates the PERSON table.

This constraint has SQL statement:

UPDATE     person p
,          p.city
,          p.area_code
) =
    SELECT     na.address
    ,          na.city
    ,          na.area_code
    FROM       new_address na
    ,          t_app_time tt
    WHERE      na.person_id = p.person_id
    AND        tt.app_year =  TO_NUMBER( TO_CHAR( na.from_date,'YYYY' ))     
    AND        tt.app_month = TO_NUMBER( TO_CHAR( na.from_date,'MM' ))
    AND        tt.app_day =   TO_NUMBER( TO_CHAR( na.from_date,'DD' ))

with transition properties:

Transition Table =    T_APP_TIME
Fire On Insert =      Never
Fire On Delete =      Never
Fire On Update =      UsedColumns

Make sure correct comparison (data type conversion) takes place between the NUMBER data in the T_APP_TIME table and the DATE data in the FROM_DATE column. Consult your RDBMS SQL documentation.


See also

The T_APP_TIME Table

The Application Timer

Starting and Stopping the Application Timer