hibernate主键生成策略

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
Java代码
@Id  
@GeneratedValue(GenerationType.AUTO)  

@Id
@GeneratedValue(GenerationType.AUTO)

就可以用hibernate特有以下用法来实现
Java代码
@GeneratedValue(generator = "paymentableGenerator")     
@GenericGenerator(name = "paymentableGenerator", strategy = "assigned")  

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


@GenericGenerator的定义:
Java代码
@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 Hibernate
  * 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,
Java代码
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
Java代码
@GeneratedValue(generator = "paymentableGenerator")     
@GenericGenerator(name = "paymentableGenerator", strategy = "native")   

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

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

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

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

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

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

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

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

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

6、select
Java代码
@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
Java代码
@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
Java代码
@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
Java代码
@GeneratedValue(generator = "paymentableGenerator")     
@GenericGenerator(name = "paymentableGenerator", strategy = "increment")   

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

10、foreign
Java代码
@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（?）
Java代码
@OneToOne(cascade = CascadeType.ALL)   
@PrimaryKeyJoinColumn   

@OneToOne(cascade = CascadeType.ALL)
@PrimaryKeyJoinColumn
例如
Java代码
@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
Java代码
@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
Java代码
@GeneratedValue(generator = "paymentableGenerator")     
@GenericGenerator(name = "paymentableGenerator", strategy = "guid")   

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

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

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

13、sequence-identity
Java代码
@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。

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