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

@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") })