Hibernate中对于主键自增策略的Annotation

关键字: hibenate @generatedvalue @genericgenerator

这里讨论代理主键，业务主键（比如说复合键等）这里不讨论。 
一、JPA通用策略生成器 
通过annotation来映射 hibernate 实体的,基于 annotation的 hibernate 主键标识为@Id, 
其生成规则由@GeneratedValue设定的.这里的@id和@GeneratedValue都是JPA的标准用法, 
JPA提供四种标准用法,由@GeneratedValue的源代码可以明显看出. 

 @Target ({METHOD,FIELD})
     @Retention (RUNTIME)
     public   @interface  GeneratedValue{
         GenerationType strategy() default  AUTO;
         String generator() default   "" ;
     }

 @Target({METHOD,FIELD})
     @Retention(RUNTIME)
     public @interface GeneratedValue{
         GenerationType strategy() default AUTO;
         String generator() default "";
     }

其中GenerationType: 

 public   enum  GenerationType{
     TABLE,
     SEQUENCE,
     IDENTITY,
     AUTO
 }

 public enum GenerationType{
     TABLE,
     SEQUENCE,
     IDENTITY,
     AUTO
 }

JPA提供的四种标准用法为TABLE,SEQUENCE,IDENTITY,AUTO. 
TABLE：使用一个特定的数据库表格来保存主键。 
SEQUENCE：根据底层数据库的序列来生成主键，条件是数据库支持序列。 
IDENTITY：主键由数据库自动生成（主要是自动增长型） 
AUTO：主键由程序控制。 

1、TABLE 

 @Id
 @GeneratedValue (strategy = GenerationType.TABLE, generator= "payablemoney_gen" )
 @TableGenerator (name =  "pk_gen" ,
     table="tb_generator" ,
     pkColumnName="gen_name" ,
     valueColumnName="gen_value" ,
     pkColumnValue="PAYABLEMOENY_PK" ,
     allocationSize=1
 )

 @Id
 @GeneratedValue(strategy = GenerationType.TABLE, generator="payablemoney_gen")
 @TableGenerator(name = "pk_gen",
     table="tb_generator",
     pkColumnName="gen_name",
     valueColumnName="gen_value",
     pkColumnValue="PAYABLEMOENY_PK",
     allocationSize=1
 )

这里应用表tb_generator，定义为 

 CREATE   TABLE   tb_generator (
   id NUMBER NOT   NULL ,
   gen_name VARCHAR2(255) NOT   NULL ,
   gen_value NUMBER NOT   NULL ,
   PRIMARY   KEY (id)
 )

 CREATE TABLE  tb_generator (
   id NUMBER NOT NULL,
   gen_name VARCHAR2(255) NOT NULL,
   gen_value NUMBER NOT NULL,
   PRIMARY KEY(id)
 )

插入纪录，供生成主键使用， 

 INSERT   INTO  tb_generator(id, gen_name, gen_value)  VALUES  (1,PAYABLEMOENY_PK', 1);

 INSERT INTO tb_generator(id, gen_name, gen_value) VALUES (1,PAYABLEMOENY_PK', 1);

在主键生成后，这条纪录的value值，按allocationSize递增。 


@TableGenerator的定义： 

 @Target ({TYPE, METHOD, FIELD})
 @Retention (RUNTIME)
 public   @interface  TableGenerator {
   String name();
   String table() default   "" ;
   String catalog() default   "" ;
   String schema() default   "" ;
   String pkColumnName() default   "" ;
   String valueColumnName() default   "" ;
   String pkColumnValue() default   "" ;
   int  initialValue()  default   0 ;
   int  allocationSize()  default   50 ;
   UniqueConstraint[] uniqueConstraints() default  {};
 }

 @Target({TYPE, METHOD, FIELD})
 @Retention(RUNTIME)
 public @interface TableGenerator {
   String name();
   String table() default "";
   String catalog() default "";
   String schema() default "";
   String pkColumnName() default "";
   String valueColumnName() default "";
   String pkColumnValue() default "";
   int initialValue() default 0;
   int allocationSize() default 50;
   UniqueConstraint[] uniqueConstraints() default {};
 }

其中属性说明： 
name属性表示该表主键生成策略的名称，它被引用在@GeneratedValue中设置的“generator”值中。 
table属性表示表生成策略所持久化的表名，例如，这里表使用的是数据库中的“tb_generator”。 
catalog属性和schema具体指定表所在的目录名或是数据库名。 
pkColumnName属性的值表示在持久化表中，该主键生成策略所对应键值的名称。例如在“tb_generator”中将 “gen_name”作为主键的键值 
valueColumnName属性的值表示在持久化表中，该主键当前所生成的值，它的值将会随着每次创建累加。例如，在 “tb_generator”中将“gen_value”作为主键的值 
pkColumnValue属性的值表示在持久化表中，该生成策略所对应的主键。例如在“tb_generator”表中，将 “gen_name”的值为“CUSTOMER_PK”。 
initialValue表示主键初识值，默认为0。 
allocationSize表示每次主键值增加的大小，例如设置成1，则表示每次创建新记录后自动加1，默认为50。 
UniqueConstraint与@Table标记中的用法类似。 

2、SEQUENCE 

 @Id
 @GeneratedValue (strategy = GenerationType.SEQUENCE,generator= "payablemoney_seq" )
 @SequenceGenerator (name= "payablemoney_seq" , sequenceName= "seq_payment" )

 @Id
 @GeneratedValue(strategy = GenerationType.SEQUENCE,generator="payablemoney_seq")
 @SequenceGenerator(name="payablemoney_seq", sequenceName="seq_payment")

@SequenceGenerator定义 

 @Target ({TYPE, METHOD, FIELD})
 @Retention (RUNTIME)
 public   @interface  SequenceGenerator {
  String name();
  String sequenceName() default   "" ;
  int  initialValue()  default   0 ;
  int  allocationSize()  default   50 ;
 }

 @Target({TYPE, METHOD, FIELD})
 @Retention(RUNTIME)
 public @interface SequenceGenerator {
  String name();
  String sequenceName() default "";
  int initialValue() default 0;
  int allocationSize() default 50;
 }

name属性表示该表主键生成策略的名称，它被引用在@GeneratedValue中设置的“generator”值中。 
sequenceName属性表示生成策略用到的数据库序列名称。 
initialValue表示主键初识值，默认为0。 
allocationSize表示每次主键值增加的大小，例如设置成1，则表示每次创建新记录后自动加1，默认为50。 


3、IDENTITY 

 @Id
 @GeneratedValue (strategy = GenerationType.IDENTITY)

 @Id
 @GeneratedValue(strategy = GenerationType.IDENTITY)

4、AUTO 

 @Id
 @GeneratedValue (strategy = GenerationType.AUTO)

 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)

在指定主键时，如果不指定主键生成策略，默认为AUTO。 

 @Id

 @Id

跟下面的定义是一样的。 

 @Id
 @GeneratedValue (strategy = GenerationType.AUTO)

 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)

二、 hibernate 主键策略生成器 
hibernate 提供多种主键生成策略，有点是类似于JPA，有的是 hibernate 特有： 
native: 对于 oracle 采用 Sequence 方式，对于MySQL 和 SQL Server 采用identity（自增主键生成机制），native就是将主键的生成工作交由数据库完成， hibernate 不 管（很常用）。 
uuid: 采用128位的uuid算法生成主键，uuid被编码为一个32位16进制数字的字符串。占用空间大（字符串类型）。 
hilo: 使用hilo生成策略，要在数据库中建立一张额外的表，默认表名为hibernate_unique_key,默认字段为integer类型，名称是 next_hi（比较少用）。 
assigned: 在插入数据的时候主键由程序处理（很常用），这是 <generator>元素没有指定时的默认生成策略。等同于JPA中的AUTO。 
identity: 使用SQL Server 和 MySQL 的自增字段，这个方法不能放到 Oracle 中，Oracle 不支持自增字段，要设定sequence（MySQL 和 SQL Server 中很常用）。 
          等同于JPA中的INDENTITY。 
select: 使用触发器生成主键（主要用于早期的数据库主键生成机制，少用）。 
sequence: 调用底层数据库的序列来生成主键，要设定序列名，不然 hibernate 无 法找到。 
seqhilo: 通过hilo算法实现，但是主键历史保存在Sequence中，适用于支持 Sequence 的数据库，如 Oracle（比较少用） 
increment: 插入数据的时候 hibernate 会给主键添加一个自增的主 键，但是一个 hibernate 实例就维护一个计数器，所以在多个实例运行的时候不能使用这 个方法。 
foreign: 使用另外一个相关联的对象的主键。通常和<one-to-one>联合起来使用。 
guid: 采用数据库底层的guid算法机制，对应MYSQL的uuid()函数，SQL Server的newid()函数，ORACLE的rawtohex(sys_guid())函数等。 
uuid.hex: 看uuid，建议用uuid替换。 
sequence-identity: sequence策略的扩展，采用立即检索策略来获取sequence值，需要JDBC3.0和JDK4以上（含1.4）版本 

hibernate 提供了多种生成器供选择,基于Annotation的方式通过 @GenericGenerator实现. 
hibernate 每种主键生成策略提供接口org. hibernate .id.IdentifierGenerator的实现类,如果要实现自定义的主键生 成策略也必须实现此接口. 

 public   interface  IdentifierGenerator {
     /**
      * The configuration parameter holding the entity name
      */
     public   static   final  String ENTITY_NAME =  "entity_name" ;

   /**
    * Generate a new identifier.
    * @param session
    * @param object the entity or toplevel collection for which the id is being generated
    *
    * @return a new identifier
    * @throws HibernateException
    */
   public  Serializable generate(SessionImplementor session, Object object)
     throws  HibernateException;
 }

 public interface IdentifierGenerator {
     /**
      * The configuration parameter holding the entity name
      */
     public static final String ENTITY_NAME = "entity_name";

   /**
    * Generate a new identifier.
    * @param session
    * @param object the entity or toplevel collection for which the id is being generated
    *
    * @return a new identifier
    * @throws HibernateException
    */
   public Serializable generate(SessionImplementor session, Object object)
     throws HibernateException;
 }

IdentifierGenerator提供一generate方法,generate方法返回产生的主键. 


三、@GenericGenerator 
自定义主键生成策略，由@GenericGenerator实现。 
hibernate 在JPA的基础上进行了扩展，可以用一下方式引入 hibernate 独有的主键生成策略，就是通过@GenericGenerator加入的。 

比如说，JPA标准用法 

 @Id
 @GeneratedValue (GenerationType.AUTO)

 @Id
 @GeneratedValue(GenerationType.AUTO)

就可以用 hibernate 特有以下用法来实现 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "assigned" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "assigned")

@GenericGenerator的定义: 

 @Target ({PACKAGE, TYPE, METHOD, FIELD})
 @Retention (RUNTIME)
 public   @interface  GenericGenerator {
  /**
   * unique generator name
   */
  String name();
  /**
   * Generator strategy either a predefined Hibernate
   * strategy or a fully qualified class name.
   */
  String strategy();
  /**
   * Optional generator parameters
   */
  Parameter[] parameters() default  {};
 }

 @Target({PACKAGE, TYPE, METHOD, FIELD})
 @Retention(RUNTIME)
 public @interface GenericGenerator {
  /**
   * unique generator name
   */
  String name();
  /**
   * Generator strategy either a predefined <span class="hilite1">Hibernate</span>

   * strategy or a fully qualified class name.
   */
  String strategy();
  /**
   * Optional generator parameters
   */
  Parameter[] parameters() default {};
 }

name属性指定生成器名称。 
strategy属性指定具体生成器的类名。 
parameters得到strategy指定的具体生成器所用到的参数。 

对于这些 hibernate 主键生成策略和各自的具体生成器之间的关系,在org. hibernate .id.IdentifierGeneratorFactory中指定了, 

 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 );
 }

 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);
 }

上面十二种策略，加上native， hibernate 一共默认支持十三种生成策 略。 

1、native 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "native" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "native")

2、uuid 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "uuid" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "uuid")

3、hilo 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "hilo" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "hilo")

4、assigned 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "assigned" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "assigned")

5、identity 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "identity" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "identity")

6、select 

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

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

7、sequence 

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

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

8、seqhilo 

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

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

9、increment 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "increment" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "increment")

10、foreign 

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

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

注意：直接使用@PrimaryKeyJoinColumn 报错（?） 

 @OneToOne (cascade = CascadeType.ALL)
 @PrimaryKeyJoinColumn

 @OneToOne(cascade = CascadeType.ALL)
 @PrimaryKeyJoinColumn

例如 

 @Entity
 public   class  Employee {
   @Id  Integer id;

   @OneToOne   @PrimaryKeyJoinColumn
   EmployeeInfo info;
   ...
 }

 @Entity
 public class Employee {
   @Id Integer id;

   @OneToOne @PrimaryKeyJoinColumn
   EmployeeInfo info;
   ...
 }

应该为 

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

   @OneToOne
   EmployeeInfo info;
   ...
 }

 @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 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "guid" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "guid")

12、uuid.hex 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy =  "uuid.hex" )

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "uuid.hex")

13、sequence-identity 

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

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

四、通过@GenericGenerator自定义主键生成策略 
如果实际应用中，主键策略为程序指定了就用程序指定的主键（assigned），没有指定就从sequence中取。 
明显上面所讨论的策略都不满足，只好自己扩展了，集成assigned和sequence两种策略。 

 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;
  }
 }

 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;
  }
 }

实际应用中，定义同sequence。 

 @GeneratedValue (generator =  "paymentableGenerator" )
 @GenericGenerator (name =  "paymentableGenerator" , strategy = "AssignedSequenceGenerator" ,
      parameters = { @Parameter (name =  "sequence" , value =  "seq_payablemoney" ) })

 @GeneratedValue(generator = "paymentableGenerator")
 @GenericGenerator(name = "paymentableGenerator", strategy = "AssignedSequenceGenerator",
      parameters = { @Parameter(name = "sequence", value = "seq_payablemoney") })

值得注意的是，定义的这种策略，就像打开了潘多拉魔盒，非常不可控。正常情况 下，不建议这么做。