Triggers (PDM)

A trigger is a segment of SQL code associated with a table or a view, which is invoked automatically whenever there is an attempt to modify data in the associated table or view with an insert, delete, or update command.

You can use triggers to enforce referential integrity (where declarative constraints are not sufficient) and to implement sequences for columns.

Trigger Templates and Template Items

A trigger template is a pre-defined form for creating triggers. PowerDesigner ships templates for each supported DBMS. Depending on the current DBMS, there are pre-defined templates for insert, update, and delete trigger types.

A template item is a reusable block of SQL script that can implement referential integrity, or do any other work on database tables. PowerDesigner ships template items for each supported DBMS. A template item is inserted into a trigger template script, or a trigger script. The template item calls a corresponding SQL macro which can implement an insert, update, delete, or error message constraint on one or more tables in the database.

You can use the PowerDesigner templates and template items, copy and edit them, or create your own from scratch. For more information, see Trigger Templates (PDM).

Creating Triggers
You can create triggers for referential integrity individually or by default, and create your own triggers from the property sheet of a table (or view, if supported by your DBMS).
Trigger and DBMS Trigger Properties
To view or edit a trigger's properties, double-click its Browser or list entry. The property sheet tabs and fields listed here are those available by default, before any customization of the interface by you or an administrator.
Rebuilding Triggers
PowerDesigner can rebuild triggers to ensure that they are attached to all tables joined by references to ensure referential integrity.
Modifying Triggers
PowerDesigner provides various methods for editing a trigger.
Trigger Naming Conventions
The pre-defined trigger templates that ship with PowerDesigner indicate naming conventions for the trigger scripts that it generates. The naming convention consists of a prefix indicating the trigger type followed by the table code.
Calling a Related Procedure in a Trigger Template
Some target databases do not accept code within a trigger statement. For these databases, a trigger template can call a related procedure as a parameter, which is defined in a procedure template. In these cases, procedure templates are listed in the list of trigger templates.
Multiple Triggers
Some DBMSs allow you to have multiple triggers of the same type (time and event) defined for any given table. Triggers of the same type are triggers that are invoked for the same insert, update, or delete event.
Defining Triggers with Multiple Events
Some DBMSs support multiple events on triggers. If such is the case, the Ellipsis button to the right of the Event box on the trigger definition tab is available.

Parent topic: Triggers and Procedures