hibernate 下的oracle Id Generator sequence
@SequenceGenerator(name="COMMONSEQ",sequenceName="COMMON_SEQ")
?@GeneratedValue(strategy = GenerationType.SEQUENCE,generator="COMMONSEQ")
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基本配置
??? @Id
??? @GeneratedValue(strategy=GenerationType.SEQUENCE)?
??? public Integer getId() {
??????? return this.id;
??? }
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?这样hibernate自动生成一个名叫hibernate_sequence的sequence
SQL> select * from USER_SEQUENCES;
??
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hibernate使用sequence的后台动作:
下面是一个save()动作,hibernate 先发出一个 select hibernate_sequence.nextval from dual;
Hibernate:
??? select
??????? hibernate_sequence.nextval
??? from
??????? dual
Hibernate:
??? insert
??? into
??????? DvdType
??????? (name, id)
??? values
??????? (?, ?)
1:typeoracle5
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用自动创建的hibernate_sequence的缺陷: 会使得多个表共用一个sequnce,造成同一个表序号不连续
TYPE表:
1:TypeExample21
2:TypeExample21
3:TypeExample21
4:TypeExample22
5:TypeExample23
6:TypeExample24
7:TypeExample25
8:TypeExample26
9:TypeExample27
10:TypeExample28
11:TypeExample29
12:TypeExample210
?QUALITY表
13:Qualityoracle5
14:QualityExample21
15:QualityExample22
16:QualityExample23
17:QualityExample24
18:QualityExample25
19:QualityExample26
20:QualityExample27
21:QualityExample28
22:QualityExample29
23:QualityExample210
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所以建议,还是为每个表定义具体的sequence name
自定义sequence
@Entity
@SequenceGenerator(name="TypeSEQ",sequenceName="TypeSEQ_DB")
public class DvdType implements java.io.Serializable {
??? @Id
??? //@GeneratedValue????????????
??? @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="TypeSEQ")
?@Entity
@SequenceGenerator(name="QualitySEQ",sequenceName="QualitySEQ_DB")
public class QualityType implements java.io.Serializable {
??? @Id
??? //@GeneratedValue
??? @GeneratedValue(strategy=GenerationType.SEQUENCE, generator="QualitySEQ")
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00:07:46,437 INFO? [STDOUT] Hibernate:
??? select
??????? TypeSEQ_DB.nextval
??? from
??????? dual
?00:08:52,437 INFO? [STDOUT] Hibernate:
??? select
??????? QualitySEQ_DB.nextval
??? from
??????? dual
?
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hibernate的sequence ,生成的id,事务间缺省是50 increment
现象:
hibernate自动生成的sequence,在oracle下看,increment_by还是1
SQL> select * from USER_SEQUENCES;
SEQUENCE_NAME?????????????????? MIN_VALUE? MAX_VALUE INCREMENT_BY C O CACHE_SIZE LAST_NUMBER
------------------------------ ---------- ---------- ------------ - - ---------- -----------
SEQUENCE_DVD_TABLE_1??????????????????? 1 1.0000E+27??????????? 1 N N????????? 0??????? 1511
USERSEQ_DB????????????????????????????? 1 1.0000E+27??????????? 1 N N???????? 20?????????? 1
GROUPSEQ_DB???????????????????????????? 1 1.0000E+27??????????? 1 N N???????? 20????????? 21
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但通过hibernate/JPA进行save/persist()操作,ID却是increment +50
SQL> insert into USERGROUP(ID,NAME) values(GROUPSEQ_DB.nextval,'group6');
1 row created.
SQL> select * from usergroup;
??????? ID NAME
---------- --------------------------------------------------
?????? 200 group1
?????? 250 group1
?????? 300 group3
?????? 350 group4
?????? 400 group5
???????? 9 group6?????????????? //这是手工insert的,上面5条记录是hibernate persist的
6 rows selected.
SQL> select GROUPSEQ_DB.nextval from dual;
?? NEXTVAL
----------
??????? 10
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原因:
1.hibernate 对sequence参数以自己为准,不读oracle的参数
2.hibernate increment缺省就是50,大概跟 hibernate集群应用有关
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解决:hibernate提供了allocationSize参数来设??????
@Entity
@SequenceGenerator(name="GroupSEQ",sequenceName="GroupSEQ_DB",allocationSize=1)
public class UserGroup {
SQL> select * from usergroup;
??????? ID NAME
---------- --------------------------------------------------
?????? 200 group1
?????? 250 group1
?????? 300 group3
?????? 350 group4
?????? 400 group5
??????? 11 group8?????????????? 这两条是用hibernate新存的
??????? 12 group9
???????? 9 group6
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