ER/Studio - Embarcadero Technologies Product Documentation

USING ER/STUDIO > DEVELOPING THE PHYSICAL MODEL
Because triggers are customizable and execute automatically, they are often used to:
• Enforce referential integrity rules. For example, when a new customer in the eastern territory is added to the
customer table, the new customer information is also added to the table for the sales representative handling
that region.
• Enforce business rules on table data. For example, restricting an order insertion based on the customer’s
account status. If the customer’s payment is overdue or the order exceeds the customer’s credit limit, the order
is rejected.
• Synchronize information in another table when a table is updated. For example, you can create a delete trigger
on the product table that the trigger uses to locate and delete matching rows in the sales table and pending
orders table.
• Initiate an action external to the SQL Server when an update occurs. For example, when a new employee is
hired and added into the employees table, an e-mail is sent to the human resources department that prompts
them to perform certain actions like arranging desk space and computer equipment, and ensuring all that all
required paperwork is sent to the new employee and is returned completed to the human resources
department.
• Prevent some types of operations, such as UPDATEs. For example, a trigger can roll back updates that
attempt to apply a bonus (stored in the renumeration table) to employees (stored in the persons table)
who work less than 16 hours a week.
You can view the triggers associated with your models from the Triggers node in the Data Model Explorer, but to
create or edit triggers, you must use the Triggers tab of the table with which you want to associate the trigger.
The generated trigger code is customized for each target database platform. ER/Studio uses templates to implement
trigger code generation. SQL Procedures can be triggers that are a special type of procedure.
ER/Studio supports the following trigger types:
• Referential Integrity Triggers ensure implied relationships in the database are enforced, by preventing users from
creating discrepancies in the database. They inform the database how to manage or process the procedural SQL
commands, which enforce the business rules of an organization. ER/Studio defines Referential Integrity Triggers
by establishing insert, update and delete options between parent and child tables.
On the Trigger tab of the Relationship Editor, you can define the level of referential integrity and SQL insert,
update, and delete behaviors. For more information, see Create a Referential Integrity Trigger.
• User-Defined Triggers are usually customized for special situations to override the default capabilities of
database generated code. User-defined triggers are closely tied to DBMS-specific code, and therefore, are
implemented only in physical models. There are three types of user-defined triggers:
• Scripted Triggers that are written in the raw procedural code of the database such as Oracle's PL/SQL or
Microsoft's Transact-SQL. You can reverse-engineer these objects if they exist on the database. You can also
display them in the Data Model Window. Reverse-engineered triggers have table names and other object
references hard-coded into their underlying code. For more information, see Create a Scripted User-Defined
Trigger.
• Templated Triggers that do not have names of specific objects the trigger references, such as table names
and specific columns hard-coded into their underlying code. This enables these triggers to be reused across
various objects of an application, and the body of the trigger code to be reused across models. For more
information, see Create a Templated User-Defined Trigger.
• Reusable Triggers that can perform actions against any number of tables. For more information, see Create a
Reusable User-Defined Trigger.
Notes
• To view triggers on the Data Model Window, you must enable them. To display triggers, click Tools > Options >
Schema Objects.
EMBARCADERO TECHNOLOGIES > ER/STUDIO® 8.0.3 USER GUIDE 187