Configuring Table and Column Information

Configuring the Primary Table

The primary table is the table into which the TopLink persistence manager persists your entity: in particular, it is the table that stores the entity's primary key (see "Configuring an EJB 3.0 Entity Primary Key"). Optionally, you can also specify one or more secondary tables (see "Configuring a Secondary Table") if the entity's persistent data is stored across multiple tables.

You define the primary table at the entity class level.

@Entity
@Table(name="EJB_EMPLOYEE")
public class Employee implements Serializable
{
...
}

Configuring a Secondary Table

Specifying one or more secondary tables indicates that the entity's persistent data is stored across multiple tables. You must first specify a primary table (see "Configuring the Primary Table") before you can specify any secondary tables.

You define a secondary table at the entity class level.

If you specify one or more secondary tables, you can specify the secondary table name in the column definition (see "Configuring a Join Column") for persistent fields that are stored in that table. This allows you to distribute the persistent fields of an entity across multiple tables.

@Entity
@Table(name="EJB_EMPLOYEE")
@SecondaryTable(name="EJB_SALARY")
public class Employee implements Serializable
{
...
}

Configuring a Column

The column is, by default, the name of the column in the primary table (see "Configuring the Primary Table") into which the TopLink persistence manager stores the field's value.

You define the column at one of the property (getter or setter method) or field level of your entity.

If you specified one or more secondary tables (see "Configuring a Secondary Table"), you can specify the secondary table name in the column definition. This allows you to distribute the persistent fields of an entity across multiple tables.

@Column(name="F_NAME")
public String getFirstName()
{
    return firstName;
}

@Column(name="SALARY", secondaryTable="EMP_SALARY")
public String getSalary()
{
    return salary;
}

Configuring a Join Column

A join column specifies a mapped, foreign key column for joining an entity association or a secondary table.

You can define a join column with a:

• secondary table (see Example 7-9)

• one-to-one mapping (see Example 7-10)

• many-to-one mapping (see Example 7-11)

• one-to-many mapping (see Example 7-12)

@Entity
@Table(name="EJB_EMPLOYEE")
@SecondaryTable(name="EJB_SALARY")
@JoinColumn(name="EMP_ID", referencedColumnName="EMP_ID")
public class Employee implements Serializable
{
...
}

@OneToOne(cascade=ALL, fetch=LAZY)
@JoinColumn(name="ADDR_ID")
public Address getAddress()
{
    return address;
}

@ManyToOne(cascade=PERSIST, fetch=LAZY)
@JoinColumn(name="MANAGER_ID", referencedColumnName="EMP_ID")
public Employee getManager()
{
    return manager;
}

@OneToMany(cascade=PERSIST)
@JoinColumn(name="MANAGER_ID", referencedColumnName="EMP_ID")
public Collection getManagedEmployees()
{
    return managedEmployees;
}