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spring data jpa 的标准主键生成策略主要有四种,分别是:
- public enum GenerationType {
- TABLE, //使用一个额外的数据库表来保存主键
- SEQUENCE,//使用序列的方式,且其底层数据库要支持序列,一般有postgres、Oracle等
- IDENTITY,//主键由数据库生成,一般为自增型主键,支持的有MySql和Sql Server
- AUTO//由程序来决定主键规则
- }
主键的生成规则主要由注解 @GeneratedValue 来说明,其源码如下:
- @Target({METHOD, FIELD})
- @Retention(RUNTIME)
- public @interface GeneratedValue {
- GenerationType strategy() default AUTO;
- String generator() default "";
- }
- @Id
- @GeneratedValue(strategy = GenerationType.SEQUENCE,generator="payablemoney_seq")
- @SequenceGenerator(name="payablemoney_seq", sequenceName="seq_payment")
使用的具体例子为:
假设有一个表示人脸图片集合的类为FaceSet,其主键为facesetToken,则表示如下
- @Entity(name = "face_set")
- public class FaceSet{
- }
- @Id
- @GeneratedValue(strategy = GenerationType.SEQUENCE,generator="faceset_generator")
- @SequenceGenerator(name="faceset_generator", sequenceName="faceset_seq")
- @Column(name = "faceset_token", unique = true)
- private String facesetToken;
- @Id
- @GeneratedValue(strategy = GenerationType.AUTO)
- private String facesetToken;
- @Id
- @GeneratedValue
- private String facesetToken;
- @Id
- private String facesetToken;
hibernate-5.0.12.Final版本的默认工厂中有14种生成策略,具体可见org.hibernate.id.factory.internal.DefaultIdentifierGeneratorFactory
- public DefaultIdentifierGeneratorFactory() {
- register( "uuid2", UUIDGenerator.class );
- register( "guid", GUIDGenerator.class ); // can be done with UUIDGenerator + strategy
- register( "uuid", UUIDHexGenerator.class ); // "deprecated" for new use
- register( "uuid.hex", UUIDHexGenerator.class ); // uuid.hex is deprecated
- register( "assigned", Assigned.class );
- register( "identity", IdentityGenerator.class );
- register( "select", SelectGenerator.class );
- register( "sequence", SequenceStyleGenerator.class );
- register( "seqhilo", SequenceHiLoGenerator.class );
- register( "increment", IncrementGenerator.class );
- register( "foreign", ForeignGenerator.class );
- register( "sequence-identity", SequenceIdentityGenerator.class );
- register( "enhanced-sequence", SequenceStyleGenerator.class );
- register( "enhanced-table", TableGenerator.class );
- }
-
- public void register(String strategy, Class generatorClass) {
- LOG.debugf( "Registering IdentifierGenerator strategy [%s] -> [%s]", strategy, generatorClass.getName() );
- final Class previous = generatorStrategyToClassNameMap.put( strategy, generatorClass );
- if ( previous != null ) {
- LOG.debugf( " - overriding [%s]", previous.getName() );
- }
- }
对几种比较常用的类型进行说明:
- @Id
- @GeneratedValue(generator = "faceset_generator")
- @GenericGenerator(name = "faceset_generator", strategy = "uuid")
- @Id
- @GeneratedValue(generator = "faceset_generator")
- @GenericGenerator(name = "faceset_generator", strategy = "assigned")
-
- @Id
- @GeneratedValue(generator = "faceset_generator")
- @GenericGenerator(name = "faceset_generator", strategy = "sequence",
- parameters = { @Parameter(name = "sequence", value = "faceset_seq") })
常用数据库支持生成规则如下:
数据库 | 支持的策略 |
---|---|
Postgres | GenerationType.TABLE GenerationType.AUTO GenerationType.IDENTITY GenerationType.SEQUENCE |
Oracle | GenerationType.TABLE GenerationType.AUTO GenerationType.SEQUENCE 不支持GenerationType.IDENTITY |
Mysql | GenerationType.TABLE GenerationType.AUTO GenerationType.IDENTITY 不支持GenerationType.SEQUENCE |
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