基于按annotation的hibernate主键生成策略

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

1. @Id
2. @GeneratedValue(GenerationType.AUTO)

@Id @GeneratedValue(GenerationType.AUTO)

就可以用hibernate特有以下用法来实现

Java代码

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

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

@GenericGenerator的定义:

Java代码

1. @Target({PACKAGE, TYPE, METHOD, FIELD}) 
2. @Retention(RUNTIME) 
3. public @interface GenericGenerator { 
5. String name(); 
7. String strategy(); 
9. Parameter[] parameters() default {}; 
10. }

@Target({PACKAGE, TYPE, METHOD, FIELD}) @Retention(RUNTIME) public @interface GenericGenerator { String name(); String strategy(); 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.IdentifierGeneratorFacto ry中指定了,

Java代码

1. static { 
2. GENERATORS.put("uuid", UUIDHexGenerator.class); 
3. GENERATORS.put("hilo", TableHiLoGenerator.class); 
4. GENERATORS.put("assigned", Assigned.class); 
5. GENERATORS.put("identity", IdentityGenerator.class); 
6. GENERATORS.put("select", SelectGenerator.class); 
7. GENERATORS.put("sequence", SequenceGenerator.class); 
8. GENERATORS.put("seqhilo", SequenceHiLoGenerator.class); 
9. GENERATORS.put("increment", IncrementGenerator.class); 
10. GENERATORS.put("foreign", ForeignGenerator.class); 
11. GENERATORS.put("guid", GUIDGenerator.class); 
12. GENERATORS.put("uuid.hex", UUIDHexGenerator.class); //uuid.hex is deprecated
13. GENERATORS.put("sequence-identity", SequenceIdentityGenerator.class); 
14. }

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
                      r.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

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

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

2、uuid

Java代码

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

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

3、hilo

Java代码

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

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

4、assigned

Java代码

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

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

5、identity

Java代码

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

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

6、select

Java代码

1. @GeneratedValue(generator = "paymentableGenerator") 
2. @GenericGenerator(name="select", strategy="select", 
3. 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

1. @GeneratedValue(generator = "paymentableGenerator") 
2. @GenericGenerator(name = "paymentableGenerator", strategy = "sequence", 
3. 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

1. @GeneratedValue(generator = "paymentableGenerator") 
2. @GenericGenerator(name = "paymentableGenerator", strategy = "seqhilo", 
3. 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

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

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

10、foreign

Java代码

1. @GeneratedValue(generator = "idGenerator") 
2. @GenericGenerator(name = "idGenerator", strategy = "foreign", 
3. 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

1. @OneToOne(cascade = CascadeType.ALL) 
2. @PrimaryKeyJoinColumn

@OneToOne(cascade = CascadeType.ALL) @PrimaryKeyJoinColumn

例如

Java代码

1. @Entity
2. public class Employee { 
3. @Id Integer id; 
4.  
5. @OneToOne @PrimaryKeyJoinColumn
6. EmployeeInfo info; 
7. ... 
8. }

@Entity public class Employee { @Id Integer id; @OneToOne @PrimaryKeyJoinColumn EmployeeInfo info; ... }

应该为

Java代码

1. @Entity
2. public class Employee { 
3. @Id
4. @GeneratedValue(generator = "idGenerator") 
5. @GenericGenerator(name = "idGenerator", strategy = "foreign", 
6. parameters = { @Parameter(name = "property", value = "info") }) 
7. Integer id; 
8.  
9. @OneToOne
10. EmployeeInfo info; 
11. ... 
12. }

@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

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

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

12、uuid.hex

Java代码

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

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

13、sequence-identity

Java代码

1. @GeneratedValue(generator = "paymentableGenerator") 
2. @GenericGenerator(name = "paymentableGenerator", strategy = "sequence-identity", 
3. 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

1. public class AssignedSequenceGenerator extends SequenceGenerator implements
2. PersistentIdentifierGenerator, Configurable { 
3. private String entityName; 
4.  
5. public void configure(Type type, Properties params, Dialect dialect) throws MappingException { 
6. entityName = params.getProperty(ENTITY_NAME); 
7. if (entityName==null) { 
8. throw new MappingException("no entity name"); 
9. } 
10.  
11. super.configure(type, params, dialect);  
12. } 
14. public Serializable generate(SessionImplementor session, Object obj) 
15. throws HibernateException { 
16.  
17. Serializable id = session.getEntityPersister( entityName, obj ) 
18. .getIdentifier( obj, session.getEntityMode() ); 
19.  
20. if (id==null) { 
21. id = super.generate(session, obj); 
22. } 
23.  
24. return id; 
25. } 
26. }

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

1. @GeneratedValue(generator = "paymentableGenerator") 
2. @GenericGenerator(name = "paymentableGenerator", strategy = "AssignedSequenceGenerator", 
3. 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。