EclipseLink和Sequence Generator预分配

默认情况下，

@SequenceGenerator

public @interface SequenceGenerator {        int initialValue() default 1;        int allocationSize() default 50;}

Eclipselink似乎使用以下公式来计算“顺序”实体标识：

entityId = initialValue - allocationSize + INCREMENT_BY

或使用DDL：

entityId = START_WITH - allocationSize + INCREMENT_BY

回到您的特殊情况：

@SequenceGenerator(     name="email-seq-gen",     sequenceName="EMAIL_SEQ_GEN",     allocationSize=500) // initialValue=1 (default)CREATE SEQUENCE EMAIL_SEQ_GEN START WITH 1 INCREMENT BY 500;

产生

entityId = 1 - 500 + 1 = -500 // Eclipselink error

@SequenceGenerator(     name="email-seq-gen",     sequenceName="EMAIL_SEQ_GEN",     initialValue=1,     allocationSize=500 )CREATE SEQUENCE EMAIL_SEQ_GEN START WITH 1 INCREMENT BY 500;

产生

entityId = 1 - 500 + 1 = -500 // Eclipselink error

@SequenceGenerator(     name="email-seq-gen",     sequenceName="EMAIL_SEQ_GEN",     initialValue=500,     allocationSize=500)CREATE SEQUENCE EMAIL_SEQ_GEN START WITH 500 INCREMENT BY 500;

产生

entityId = 500 - 500 + 500 = 500 // fine, but inappropriateentityId = 500 - 500 + 1000 = 1000 // incremented by 500entityId = 500 - 500 + 1500 = 1500 // incremented by 500...

为了满足您的要求，应使用以下一种：

@SequenceGenerator(     name="email-seq-gen",     sequenceName="EMAIL_SEQ_GEN",     allocationSize=500 ) // initialValue=1 (default) but 'START WITH'=500CREATE SEQUENCE EMAIL_SEQ_GEN START WITH 500 INCREMENT BY 1;

产生

entityId = 500 - 500 + 1 = 1entityId = 500 - 500 + 2 = 2entityId = 500 - 500 + 3 = 3...

可以使用以下SQL
命令从基础数据库中删除现有序列：

DROP SEQUENCE email_seq_gen RESTRICT;

希望对您有所帮助。