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)

@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")

@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 {};

}

@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);

}

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")

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

2、uuid

Java代码

@GeneratedValue(generator =
"paymentableGenerator")

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

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

3、hilo

Java代码

@GeneratedValue(generator =
"paymentableGenerator")

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

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

4、assigned

Java代码

@GeneratedValue(generator =
"paymentableGenerator")

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

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

5、identity

Java代码

@GeneratedValue(generator =
"paymentableGenerator")

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

@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") })

@GeneratedValu
4000
e(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") })

@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") })

@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")

@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") })

@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

@OneToOne(cascade = CascadeType.ALL) @PrimaryKeyJoinColumn

例如

Java代码

@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

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;

...

}

@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")

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

12、uuid.hex

Java代码

@GeneratedValue(generator =
"paymentableGenerator")

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

@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") })

@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;

}

}

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。