JPA实体注解与hibernate主键生成策略

JPA实体注解与hibernate主键生成策略

<wbr><wbr>用hibernate注解开发项目，对于主键的生成策略有些模糊，下面是从新浪网里面看到的一篇关于hibernate注解以及主键生成策略的文章，值得一看：</wbr></wbr>

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1. 实体标志:

<wbr><wbr><wbr></wbr></wbr></wbr>@Entity
<wbr><wbr><wbr>@Indexed(index="group")<br><wbr><wbr><wbr>@Table(name="GROUP_LAYMOD")</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr><wbr>* @Indexed 标识需要进行索引的对象，<br><wbr><wbr><wbr>* 属性 : index 指定索引文件的路径 @DocumentId 用于标示实体类中的唯一的属性保存在索引文件中，是当进行全文检索时可以这个唯一的属性来区分索引中其他实体对象，一般使用实体类中的主键属性<br><wbr><wbr><wbr>* @Field 标注在类的get属性上，标识一个索引的Field<br><wbr><wbr><wbr><wbr><wbr>属性 : index 指定是否索引，与Lucene相同<br><wbr><wbr><wbr><wbr><wbr>store 指定是否索引，与Lucene相同<br><wbr><wbr><wbr><wbr><wbr>name 指定Field的name，默认为类属性的名称<br><wbr><wbr><wbr><wbr><wbr>analyzer 指定分析器</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

在hibernate注解主键的时候，一般会使用到这两个。
<wbr><wbr>@GeneratedValue的作用是JPA的默认实现自定义主键生成策略<br><wbr><wbr>@GenericGenerator是hibernate在JPA的基础上增强。</wbr></wbr></wbr></wbr>

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

@Id<wbr><wbr><br> @GeneratedValue(GenerationType.AUTO)<wbr><wbr><br><br> 就可以用hibernate特有以下用法来实现<br><br><strong>@GeneratedValue(generator<wbr>=<wbr>"paymentableGenerator")<wbr><wbr><wbr><wbr><wbr><br> @GenericGenerator(name<wbr>=<wbr>"paymentableGenerator",<wbr>strategy<wbr>=<wbr>"assigned")<wbr><wbr><br></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></strong><br><br> @GenericGenerator的定义:<br><br> @Target({PACKAGE,<wbr>TYPE,<wbr>METHOD,<wbr>FIELD})<wbr><wbr><wbr><br> @Retention(RUNTIME)<wbr><wbr><wbr><br> public<wbr>@interface<wbr>GenericGenerator<wbr>{<wbr><wbr><wbr><br><wbr><wbr><br> String<wbr>name();<wbr><wbr><wbr><br><wbr><wbr><br> String<wbr>strategy();<wbr><wbr><wbr><br><wbr><wbr><br> Parameter[]<wbr>parameters()<wbr>default<wbr>{};<wbr><wbr><wbr><br> }<wbr><wbr><br><br><br> name属性指定生成器名称。<br> strategy属性指定具体生成器的类名。<br> parameters得到strategy指定的具体生成器所用到的参数。<br><br> 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<wbr>ry中指定了,<br><br> static<wbr>{<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("uuid",<wbr>UUIDHexGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("hilo",<wbr>TableHiLoGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("assigned",<wbr>Assigned.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("identity",<wbr>IdentityGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("select",<wbr>SelectGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("sequence",<wbr>SequenceGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("seqhilo",<wbr>SequenceHiLoGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("increment",<wbr>IncrementGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("foreign",<wbr>ForeignGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("guid",<wbr>GUIDGenerator.class);<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("uuid.hex",<wbr>UUIDHexGenerator.class);<wbr>//uuid.hex<wbr>is<wbr>deprecated<wbr><wbr><wbr><br><wbr><wbr><wbr>GENERATORS.put("sequence-identity",<wbr>SequenceIdentityGenerato<wbr>r.class);<wbr><wbr><wbr><br> }<wbr><wbr><br><br> 上面十二种策略，加上native，hibernate一共默认支持十三种生成策略。<br><br> 1、native<br> Java代码<br> @GeneratedValue(generator<wbr>=<wbr>"paymentableGenerator")<wbr><wbr><wbr><wbr><wbr><br> @GenericGenerator(name<wbr>=<wbr>"paymentableGenerator",<wbr>strategy<wbr>=<wbr>"native")<wbr><wbr><wbr><br><br> 2、uuid<br> Java代码<br> @GeneratedValue(generator<wbr>=<wbr>"paymentableGenerator")<wbr><wbr><wbr><wbr><wbr><br> @GenericGenerator(name<wbr>=<wbr>"paymentableGenerator",<wbr>strategy<wbr>=<wbr>"uuid")<wbr><wbr><wbr><br><br> 3、hilo<br> Java代码<br> @GeneratedValue(generator<wbr>=<wbr>"paymentableGenerator")<wbr><wbr><wbr><wbr><wbr><br> @GenericGenerator(name<wbr>=<wbr>"paymentableGenerator",<wbr>strategy<wbr>=<wbr>"hilo")<wbr><wbr><wbr><br><br> 4、assigned<br> Java代码<br> @GeneratedValue(generator<wbr>=<wbr>"paymentableGenerator")<wbr><wbr><wbr><wbr><wbr><br> @GenericGenerator(name<wbr>=<wbr>"paymentableGenerator",<wbr>strategy<wbr>=<wbr>"assigned")<wbr><wbr><wbr><br><br> 5、identity<br> Java代码<br> @GeneratedValue(generator<wbr>=<wbr>"paymentableGenerator")<wbr><wbr><wbr><wbr><wbr><br> @GenericGenerator(name<wbr>=<wbr>"paymentableGenerator",<wbr>strategy<wbr>=<wbr>"identity")<wbr><wbr><wbr><br><br> 6、select<br> Java代码<br> @GeneratedValue(generator<wbr>=<wbr>"paymentableGenerator")<wbr><wbr><wbr><br> @GenericGenerator(name="select",<wbr>strategy="select",<wbr><wbr><wbr><br><wbr><wbr><wbr><wbr><wbr><wbr>parameters<wbr>=<wbr>{<wbr>@Parameter(name<wbr>=<wbr>"key",<wbr>value<wbr>=<wbr>"idstoerung")<wbr>})<wbr><wbr><br><br> 7、sequence<br> Java代码<br> @GeneratedValue(generator<wbr>=<wbr>"paymentableGenerator")<wbr><wbr><wbr><br> @GenericGenerator(name<wbr>=<wbr>"paymentableGenerator",<wbr>strategy<wbr>=<wbr>"sequence",<wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>