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") })??

@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") })??

@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; ???? ... ??}??

@Entitypublic 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; ???? ... ??}??

@Entitypublic 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") })??

@GeneratedValue(generator = "paymentableGenerator")@GenericGenerator(name = "paymentableGenerator", strategy = "AssignedSequenceGenerator",      parameters = { @Parameter(name = "sequence", value = "seq_payablemoney") })