Chapter 8 Creating J2EE Applications for BEA WebLogic

Defining a mapping for a Relationship

Relationships between Entity Beans are represented in PowerDesigner using associations between Bean classes.

An association mapping defines the navigation between its classes from a database perspective. A Data Source identifies association mappings. An Association Mapping contains a list of source references, tables or views. Usually in case of one-to-one or one-to-many relationships, associations have a reference as source. In case of many-to-many relationships, associations have an associative table as source.

From an association mapping, up to six SQL queries are automatically computed to show how associated class instances can be retrieved from, or modified in the database. These six SQL queries are respectively:

• A select statement for the role A: to retrieve related class A instances for the role A defined on the class B from the database.
• An insert statement for the role A: to associate an instance of the class A with the class B.
• A delete statement for the role A: to delete from the class B the association with a class A.
• A select statement for the role B: to retrieve related class B instances for the role B defined on the class A from the database.
• An insert statement for the role B: to associate an instance of the class B with the class A.
• A delete statement for the role B: to delete from the class A the association with the class B.

These SQL queries are computed only when their corresponding roles are navigable. Insert and Delete queries for each role are only computed when an associative table is defined as source for the association.

As for class mappings, these queries are not used for WebLogic.

For WebLogic, the following extended attributes are available for associations in order to perform optimizations on relationships between beans:

• group-name-roleA
• group-name-roleB

For more information on groups, see Groups.

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