亚洲人成www在线播放,国产精品日本亚洲777,亚洲国产综合无码一区

基于按annotation的hibernate主鍵生成策略

自定義主鍵生成策略，由@GenericGenerator實現。
hibernate在JPA的基礎上進行了擴展，可以用一下方式引入hibernate獨有的主鍵生成策略，就是通過@GenericGenerator加入的。

比如說，JPA標準用法
Java代碼
@Id
@GeneratedValue(GenerationType.AUTO)

就可以用hibernate特有以下用法來實現
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "assigned")

@GenericGenerator的定義:
Java代碼
@Target({PACKAGE, TYPE, METHOD, FIELD})
@Retention(RUNTIME)
public @interface GenericGenerator {

String name();

String strategy();

Parameter[] parameters() default {};
}

name屬性指定生成器名稱。
strategy屬性指定具體生成器的類名。
parameters得到strategy指定的具體生成器所用到的參數。

對于這些hibernate主鍵生成策略和各自的具體生成器之間的關系,在org.hibernate.id.IdentifierGeneratorFactory中指定了,
Java代碼
static {
   GENERATORS.put("uuid", UUIDHexGenerator.class);
   GENERATORS.put("hilo", TableHiLoGenerator.class);
   GENERATORS.put("assigned", Assigned.class);
   GENERATORS.put("identity", IdentityGenerator.class);
   GENERATORS.put("select", SelectGenerator.class);
   GENERATORS.put("sequence", SequenceGenerator.class);
   GENERATORS.put("seqhilo", SequenceHiLoGenerator.class);
   GENERATORS.put("increment", IncrementGenerator.class);
   GENERATORS.put("foreign", ForeignGenerator.class);
   GENERATORS.put("guid", GUIDGenerator.class);
   GENERATORS.put("uuid.hex", UUIDHexGenerator.class); //uuid.hex is deprecated
   GENERATORS.put("sequence-identity", SequenceIdentityGenerator.class);
}

上面十二種策略，加上native，hibernate一共默認支持十三種生成策略。

1、native
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "native")

2、uuid
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "uuid")

3、hilo
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "hilo")

4、assigned
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "assigned")

5、identity
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "identity")

6、select
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name="select", strategy="select",
      parameters = { @Parameter(name = "key", value = "idstoerung") })

7、sequence
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "sequence",
          parameters = { @Parameter(name = "sequence", value = "seq_payablemoney") })

8、seqhilo
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "seqhilo",
          parameters = { @Parameter(name = "max_lo", value = "5") })

9、increment
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "increment")

10、foreign
Java代碼
@GeneratedValue(generator = "idGenerator")
@GenericGenerator(name = "idGenerator", strategy = "foreign",
          parameters = { @Parameter(name = "property", value = "employee") })

注意：直接使用@PrimaryKeyJoinColumn 報錯（?）
Java代碼
@OneToOne(cascade = CascadeType.ALL)
@PrimaryKeyJoinColumn
例如
Java代碼
@Entity
public class Employee {
  @Id Integer id;

  @OneToOne @PrimaryKeyJoinColumn
   EmployeeInfo info;

}
應該為
Java代碼
@Entity
public class Employee {
  @Id
  @GeneratedValue(generator = "idGenerator")
  @GenericGenerator(name = "idGenerator", strategy = "foreign",
          parameters = { @Parameter(name = "property", value = "info") })
   Integer id;

  @OneToOne
   EmployeeInfo info;

}
11、guid
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "guid")

12、uuid.hex
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "uuid.hex")

13、sequence-identity
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "sequence-identity",
          parameters = { @Parameter(name = "sequence", value = "seq_payablemoney") })

四、通過@GenericGenerator自定義主鍵生成策略
如果實際應用中，主鍵策略為程序指定了就用程序指定的主鍵（assigned），沒有指定就從sequence中取。
明顯上面所討論的策略都不滿足，只好自己擴展了，集成assigned和sequence兩種策略。

Java代碼
public class AssignedSequenceGenerator extends SequenceGenerator implements
PersistentIdentifierGenerator, Configurable {
private String entityName;

public void configure(Type type, Properties params, Dialect dialect) throws MappingException {
   entityName = params.getProperty(ENTITY_NAME);
  if (entityName==null) {
   throw new MappingException("no entity name");
   }

  super.configure(type, params, dialect);
}

public Serializable generate(SessionImplementor session, Object obj)
  throws HibernateException {

   Serializable id = session.getEntityPersister( entityName, obj )
     .getIdentifier( obj, session.getEntityMode() );

  if (id==null) {
    id = super.generate(session, obj);
   }

  return id;
}
}

實際應用中，定義同sequence。
Java代碼
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "AssignedSequenceGenerator",
      parameters = { @Parameter(name = "sequence", value = "seq_payablemoney") })

值得注意的是，定義的這種策略，就像打開了潘多拉魔盒，非常不可控。正常情況下，不建議這么做。

posted on 2010-03-15 21:50 王總兵閱讀(649) 評論(0) 編輯收藏

新用戶注冊刷新評論列表


只有注冊用戶登錄后才能發表評論。




網站導航: 博客園 IT新聞 Chat2DB C++博客博問管理

沉睡森林@漂在北京

隨筆分類(115)

隨筆檔案(154)

技術blog

搜索

最新評論