Spring Data JPA 標準用法
- spring data jpa 的標準主鍵生成策略主要有四種,分別是:
public enum GenerationType {
TABLE,
SEQUENCE,
IDENTITY,
AUTO
}
- 主鍵的生成規則主要由註解 @GeneratedValue 來說明,其源碼如下:
@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")
- 使用的具體例子爲:
假設有一個表示人臉圖片集合的類爲FaceSet,其主鍵爲facesetToken,則表示如下
@Entity(name = "face_set")
public class FaceSet{
}
- Sequence
@SequenceGenerator 中的 sequenceName 爲序列的名稱,需要與@GeneratedValue 中的generator對應
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE,generator="faceset_generator")
@SequenceGenerator(name="faceset_generator", sequenceName="faceset_seq")
@Column(name = "faceset_token", unique = true)
private String facesetToken;
- Auto
如果不指定具體的生成規則,則默認爲AUTO,即下列兩種情況等價
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private String facesetToken;
@Id
private String facesetToken;
Hibernate主鍵策略生成
- hibernate-5.0.12.Final版本的默認工廠中有14種生成策略,具體可見org.hibernate.id.factory.internal.DefaultIdentifierGeneratorFactory
public DefaultIdentifierGeneratorFactory() {
register( "uuid2", UUIDGenerator.class );
register( "guid", GUIDGenerator.class );
register( "uuid", UUIDHexGenerator.class );
register( "uuid.hex", UUIDHexGenerator.class );
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() );
}
}
- uuid
採用128位的uuid算法生成主鍵,uuid被編碼爲一個32位16進制數字的字符串。
當使用strategy爲uuid時,使用的時hibernate自己定義的UUID生成算法,此策略已過時,其具體實現參照org.hibernate.id. UUIDHexGenerator, 生成的字符串如402880876359adeb016359ae27190000
當使用strategy爲uuid2時,此爲此版本推薦使用的uuid生成算法,其默認採用標準的生成策略StandardRandomStrategy,實現爲使用jdk自帶的uuid生成方法,生成的字符串如
4af17c8e-8317-43e9-aff9-12d5590a71c6
@Id
@GeneratedValue(generator = "faceset_generator")
@GenericGenerator(name = "faceset_generator", strategy = "uuid")
- assigned
插入主鍵時,由程序來指定。相當於JPA中的AUTO。
@Id
@GeneratedValue(generator = "faceset_generator")
@GenericGenerator(name = "faceset_generator", strategy = "assigned")
- sequence
@Id
@GeneratedValue(generator = "faceset_generator")
@GenericGenerator(name = "faceset_generator", strategy = "sequence",
parameters = { @Parameter(name = "sequence", value = "faceset_seq") })
- guid
採用數據庫底層的guid算法機制,對應MYSQL的uuid()函數,SQL Server的newid()函數,ORACLE的rawtohex(sys_guid())函數等
通過@GenericGenerator自定義主鍵生成策略、
- 常用數據庫支持生成規則如下: