Mapping with Annotations - Beginning Hibernate: From Novice to Professional - page 110

public static class AccountPk {
// ...
}
}
Regardless of which of these approaches we take to declare our compound primary key,
the table that will be used to represent it will require the same set of columns. Listing 6-9
shows the DDL that will be generated from any of Listings 6-6, 6-7, or 6-8.
Listing 6-9. The DDL Generated from the Annotated Account Class (Regardless of the
Approach Used)
create table Account (
code varchar(255) not null,
number integer not null,
description varchar(255),
primary key (code, number)
);
Database Table Mapping with @Table and @SecondaryTable
The @Table annotation allows you to specify the details of the table that will be used to per-
sist the entity in the database. If you omit the annotation, Hibernate will default to using
the class name for the table name, so you only need to provide this annotation if you want
to override that behavior. The @Table annotation provides four attributes, allowing you to
override the name of the table, its catalog, and its schema, and enforce unique constraints
on columns in the table. Typically, you would only provide a substitute table name thus:
@Table(name=" ORDER_HISTORY") . The unique constraints will be applied if the database
schema is generated from the annotated classes, and will supplement any column-specific
constraints (see discussions of @Column and @JoinColumn later in this chapter). They are not
otherwise enforced.
The @SecondaryTable annotation provides a way to model an entity bean that is persisted
across several different database tables. Here, in addition to providing an @Table annotation for
the primary database table, your entity bean can have an @SecondaryTable annotation, or an
@SecondaryTables annotation in turn containing zero or more @SecondaryTable annotations.
The @SecondaryTable annotation takes the same basic attributes as the @Table annotation, with
the addition of the join attribute. The join attribute defines the join column for the primary
database table. It accepts an array of javax.persistence.PrimaryKeyJoinColumn objects. If you
omit the join attribute, then it will be assumed that the tables are joined on identically named
primary key columns.
When an attribute in the entity is drawn from the secondary table, it must be marked with
the @Column annotation, with a table attribute identifying the appropriate table. Listing 6-10
shows how a property of the Customer entity could be drawn from a second table mapped in
this way.