Revision as of 13:42, 16 June 2011

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Key API

• @SecondaryTable
• @PrimaryKeyJoinColumn

@SecondaryTable

You can use the @SecondaryTable annotation or <secondary-table> XML element to configure an entity to map to multiple tables. When an entity instance is persisted, it will insert into each of the tables. When an entity instance is read, the tables will be joined. This allows for the entity to define mappings that make use of any of the columns in any of the tables.

Secondary tables should only be used when the entity logically has its data spread across multiple tables. If the tables represent relationships, then this is better modeled using relationship mappings such as OneToOne and OneToMany.

For more information, see Section 11.1.xx "SecondaryTableAnnotation" in the JPA Specification.

@SecondaryTable Attributes

Attribute	Description	Default	Required?
name	The name of the table		Yes
catalog	A String catalog name.	Default catalog for database	No
schema	The String name of the schema.	Default schema of the database	No
uniqueConstraints	This is used only by DDL generation. By default only a primary key and foreign key constraints are defined, if desired set the value of this attribute to an array of one or more UniqueConstraint instances. For more information, see Section 11.1.49 "UniqueConstraint Annotation" in the JPA Specification.	No additional constraints	No

The following example shows how to use this annotation to specify the table for Employee.

Example: Using @Table

@Entity
@Table(name="EMP")
@SecondaryTable(name="SALARY")
public class Employee implements Serializable {
    ...
    @Id
    public Long getId() {
        return id;
    }
    ...
}

Example: Using <table-generator>

<entity class="Employee">
    <table name="EMP"/>
    <secondary-table name="SALARY"/>
    <attributes>
        <id name="id"/>
        ...
    </attributes>
</entity>

Advanced Multiple Table Configuration

@Table	Configuring Entities	Configuring Mappings
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