@GeneratedValue four standard usages are table,sequence,identity,auto.

First, the JPA generic policy generator
With annotation to map hibernate entities, the annotation-based Hibernate primary key is identified as @id,
The generation rules are set by @generatedvalue. The @id and @generatedvalue here are the standard uses of JPA,
JPA provides four standard usages, which can be clearly seen by the @generatedvalue source code.

Java code @Target ({Method,field}) @Retention (RUNTIME) public @interface generatedvalue{Generat             Iontype strategy () default AUTO;         String generator () default ""; }

Among them GenerationType:

Java code public enum generationtype{TABLE, SEQUENCE, IDENTITY, AUTO}

The four standard usages provided by JPA are table,sequence,identity,auto.
Table: Use a specific database table to hold the primary key.
SEQUENCE: Generates a primary key based on the sequence of the underlying database, provided the database supports the sequence.
IDENTITY: Primary key is automatically generated by the database (mainly auto-growth type)
AUTO: The primary key is controlled by the program.

1. TABLE
Java Code @Id @GeneratedValue (strategy = generationtype.table, generator= "Payablemoney_gen") @TableGenerator (name = "PK _gen ", table=" Tb_generator ", pkcolumnname=" Gen_name ", valuecolumnname=" Gen_value ", pkcolumnvalue=" PAYABLEMOENY_PK ", allocationsize=1)

This applies the table tb_generator, defined as
SQL code CREATE TABLE tb_generator (ID number not NULL, Gen_name VARCHAR2 (255) isn't null, gen_value number not NULL, PRIMARY KEY (ID))

Insert record for generating primary key to use,
SQL code INSERT into tb_generator (ID, gen_name, gen_value) VALUES (1,PAYABLEMOENY_PK ', 1);

After the primary key is generated, the value of this record is incremented by Allocationsize.


Definition of @TableGenerator:
Java Code    @Target ({Type, method, field})     @Retention (RUNTIME)    public  @interface  TableGenerator {     string name ();      string table ()  default  "";     string catalog ()  default   "";     string schema ()  default  ";     string  pkcolumnname ()  default  "";     string valuecolumnname ()  default   "";     string pkcolumnvalue ()