TRIGGER PROCEDURE statement

TRIGGER PROCEDURE statement

Defines a schema trigger.

Syntax
TRIGGER PROCEDURE FOR event OF object [ options ]
event

The event for which the schema trigger is being defined. The Valid events are CREATE, DELETE, FIND, WRITE, and ASSIGN.

object

The object on which the event is defined. If the event is CREATE, DELETE, FIND, or WRITE, the object must be a reference to a database table. If the event is ASSIGN, the object must be a reference to a database field qualified by a table name.

options

Optional parts of the trigger header.

Headers for CREATE, DELETE, and FIND triggers take no options. Their syntaxes are as follows:
Syntax
TRIGGER PROCEDURE FOR CREATE OF table 
Syntax
TRIGGER PROCEDURE FOR DELETE OF table 
Syntax
TRIGGER PROCEDURE FOR FIND OF table 
In the header for a WRITE trigger you can optionally include one or two buffer names.
Syntax
TRIGGER PROCEDURE FOR WRITE OF table 
  [ NEW [ BUFFER ] buffer-name1 ]
  [ OLD [ BUFFER ] buffer-name2 ]
In the header for an ASSIGN trigger, you can optionally specify one or two value holders. You can specify formatting for each as follows:
Syntax
TRIGGER PROCEDURE FOR ASSIGN
  {     { OF table .field }
     |  { NEW [ VALUE ] value1 
            { AS data-type | LIKE db-field }
        }
  }
  [ COLUMN-LABEL label ]
  [ FORMAT format-string ]
  [ INITIAL constant ]
  [ LABEL label-string ]
  [ NO-UNDO ]
  [ OLD [ VALUE ] value2 
      { AS data-type | LIKE db-field }
      [ COLUMN-LABEL label ]
      [ FORMAT format-string ]
      [ INITIAL constant ]
      [ LABEL label-string ]
      [ NO-UNDO ]
  ]
Example

The following is a WRITE trigger for the Customer table. It uses the OLD BUFFER option so that it can determine whether the CustNum value has changed. If the Customer’s outstanding balance exceeds its Credit Limit, the trigger returns the error condition (in which case the record is not updated).
r-wrcust.p
TRIGGER PROCEDURE FOR WRITE OF Customer OLD BUFFER oldCustomer.
 
/* Variable Definitions */
DEFINE VARIABLE ix          AS INTEGER NO-UNDO.
DEFINE VARIABLE Outstanding AS INTEGER NO-UNDO.
 
/* Check to see if the user changed the Customer Number */
IF Customer.CustNum <> oldCustomer.CustNum 
  AND oldCustomer.CustNum <> 0 THEN DO:
  /* If the user changed the Customer Number, find all related Orders and
     change their Customer numbers. */
  FOR EACH order OF oldCustomer:
    Order.CustNum = Customer.CustNum.
    ix = ix + 1.
  END.
  IF ix > 0 THEN
    MESSAGE ix "Orders changed to reflect the new Customer number!".
END.
 
/* Ensure that the Credit Limit value is always greater than the sum of
   this Customer’s outstanding balance */
FOR EACH Order OF Customer NO-LOCK:
  FOR EACH OrderLine OF Order NO-LOCK:
    Outstanding = Outstanding + (OrderLine.Qty * OrderLine.Price).
  END.
END.
FOR EACH Invoice OF Customer NO-LOCK:
  Outstanding = Outstanding + 
    (Invoice.Amount - (Invoice.TotalPaid + Invoice.Adjustment)).
END.
 
IF Customer.CreditLimit < Outstanding THEN DO:
  MESSAGE "This Customer has an outstanding balance of: " Outstanding 
    ".  The Credit Limit MUST exceed this amount!".
  RETURN ERROR.
END. 
Notes

Use the Data Dictionary to associate a trigger procedure with a table or field in the database.

Some 3GL applications execute schema triggers. Triggers might also be executed in batch mode. Therefore, you should avoid any user-interface interactions within schema trigger procedures.

See also

PROCEDURE statement