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 {
- String name();
- String strategy();
- Parameter[] parameters() default {};
- }
@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,
- 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
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
- @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。