基于按annotation的hibernate主键生成策略-阿里云开发者社区

基于按annotation的hibernate主键生成策略

2017-12-07 1589

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简介：

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)
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")
@GenericGenerator的定义:
Java代码
@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.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);
}
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")
2、uuid
Java代码
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "uuid")
3、hilo
Java代码
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "hilo")
4、assigned
Java代码
@GeneratedValue(generator = "paymentableGenerator")
@GenericGenerator(name = "paymentableGenerator", strategy = "assigned")
5、identity
Java代码
@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") })
7、sequence
Java代码
@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") })
9、increment
Java代码
@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") })
注意：直接使用@PrimaryKeyJoinColumn 报错（?）
Java代码
@OneToOne(cascade = CascadeType.ALL)
@PrimaryKeyJoinColumn
例如
Java代码
@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;

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

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。

本文转自博客园沉睡森林@漂在北京的博客，原文链接：基于按annotation的hibernate主键生成策略，如需转载请自行联系原博主。

基于按annotation的hibernate主键生成策略

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