基于按annotation的hibernate主键生成策略

转：http://blog.sina.com.cn/s/blog_55bba7c10100f2oh.html

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.IdentifierGeneratorFacto

ry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。

基于按annotation的hibernate主键生成策略

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