Defining Hibernate Basic O/R Mappings

There are two kinds of classes in Hibernate, entity classes and value type classes. Entity classes have their own database identities, mapping files and life cycles, while value type classes don't have. Value type classes depend on entity classes. Value type classes are also called component classes.

Hibernate uses mapping files to define the mapping metadata. Each mapping file <Class>.hbm.xml can contain metadata for one or many classes. PowerDesigner uses the following grouping strategy:

A separate mapping file is generated for each single entity class that is not in an inheritance hierarchy.
A separate mapping file is generated for each inheritance hierarchy that has a unique mapping strategy. All mappings of subclasses are defined in the mapping file. The mapping file is generated for the root class of the hierarchy. See Defining Hibernate Inheritance Mappings for details about how the mapping strategy is determined.
No mapping file is generated for a single value type class that is not in an inheritance hierarchy. Its mapping is defined in its owner's mapping file.

Defining Hibernate Class Mapping Options
Classes can be mapped to tables or views. Since views have many constraints and limited functionality (for example they do not have primary keys and reference keys), some views cannot be updated, and the mappings may not work properly in some cases.
Defining Primary Identifier Mappings
Primary identifier mapping is mandatory in Hibernate. Primary identifiers of classes are mapped to primary keys of master tables in data sources. If not defined, a default primary identifier mapping will be generated, but this may not work properly.
Defining Attribute Mappings
Attributes can be migrated attributes or ordinary attributes. Ordinary attributes can be mapped to columns or formulas. Migrated attributes do not require attribute mapping.

Parent topic: Generating Hibernate Persistent Objects