花非花

@SecondaryTable,@SecondaryTables允许你把一个entity映射到多表上,有点类似于主从表的概念,其实也是一对一或者一对多关系映射的简化版.举个简单例子,如Customer有属性street,city,state.这三个属性构成了顾客的地址,我们希望把此3个属性映射到另一张表上，作为主表的从表,此表跟主表就是一对一关系，通过address_id进行主键关联.那么,我们的Customer来应该像这样:

@Entity
@Table(name = "CUSTOMER")
@SecondaryTable(name = "EMBEDDED_ADDRESS",pkJoinColumns={@PrimaryKeyJoinColumn(name = "ADDRESS_ID")})
public class Customer implements java.io.Serializable
{
   private int id;
   private String first;
   private String last;
   private String street;
   private String city;
   private String state;
   private String zip;
  ........

  ........

@SecondaryTable的name指定表名,pkJoinColumns指定从表关联的主键,还没完,必须给street,city,state指定表名:

@Column(name = "STREET", table = "EMBEDDED_ADDRESS")
   public String getStreet()
   {
      return street;
   }

   public void setStreet(String street)
   {
      this.street = street;
   }

   @Column(name = "CITY", table = "EMBEDDED_ADDRESS")
   public String getCity()
   {
      return city;
   }

   public void setCity(String city)
   {
      this.city = city;
   }

   @Column(name = "STATE", table = "EMBEDDED_ADDRESS")
   public String getState()
   {
      return state;
   }

   public void setState(String state)
   {
      this.state = state;
   }

   @Column(name = "ZIP", table = "EMBEDDED_ADDRESS")
   public String getZip()
   {
      return zip;
   }

   public void setZip(String zip)
   {
      this.zip = zip;
   }

不错吧,是个很不错的功能,ejb3的大规模应用值的期待.