Hibernate配置說明

首先以父子關係爲例：

<

對應生成的DDL drop table PARENT;

Java代碼

drop table CHILD;
create table PARENT (ID INTEGER not null generated by default as identity, primary key (ID););;
create table CHILD (ID INTEGER not null generated by default as identity, PARENTID INTEGER, primary key (ID););;
alter table CHILD add constraint FK3D1FCFC74B18345 foreign key (PARENTID); references PARENT;

drop table CHILD; 
create table PARENT (ID INTEGER not null generated by default as identity, primary key (ID););; 
create table CHILD (ID INTEGER not null generated by default as identity, PARENTID INTEGER, primary key (ID););; 
alter table CHILD add constraint FK3D1FCFC74B18345 foreign key (PARENTID); references PARENT;

*大寫的部分inverse="true"表示 ParentPO 本身不維護表之間的關係！，而由想反的一方 children來維護，

*CASCADE=“ALL”表示無論是update,insert ,delete 都保持幾連關係

*lazy="true"表示初始化父親的時候不會把所有的兒子都從數據庫中load進來。

下面先看一下幾個例子：

生成的SQL:

Java代碼

Hibernate: insert into PARENT (ID); values (default);
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);

Hibernate: insert into PARENT (ID); values (default); 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);

結果 C:/Myapp/SQLLIB/BIN>db2 select * from child

Java代碼

ID PARENTID
----------- -----------
71 44
72 44
73 44
C:/Myapp/SQLLIB/BIN>db2 select * from parent
ID
-----------
44

ID          PARENTID 
----------- ----------- 
         71          44 
         72          44 
         73          44 
C:/Myapp/SQLLIB/BIN>db2 select * from parent 
 
ID 
----------- 
         44

注意之只有一句：session.save(parent);就把兩個兒子保存進了數據庫。

*首先講講inverse=true作用：這裏關係是由兒子維護的，所以如果只是往父親里加入兒子，不給兒子設置父親的話session.save(parent)，就不會保存兒子！看這個例子：注意與例子1的對比

Java代碼

*ChildPO child = new ChildPO(parent);---〉ChildPO child = new ChildPO();，
ITxMgr tx = null;
tx = HibernateTxMgr.beginTrans("Add a new relationships...");;
session = (Session); tx.getSession();;
parent = new ParentPO();;
ChildPO child = new ChildPO();;
ChildPO child2 = new ChildPO();;
List list = new ArrayList();;
list.add(child);;
list.add(child2);;
parent.setChildren(list);;
session.save(parent);;
session.flush();;
System.out.println("dddddddddddddddddddddddddddddddddddddddddddddddddddddd"); ;
ChildPO child3 = new ChildPO();;
child3.setParent(parent);;
session.save(child3);;
session.flush();;
System.out.println("eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"); ;
tx.endTrans();;

*ChildPO child = new ChildPO(parent);---〉ChildPO child = new ChildPO();， 

                ITxMgr tx = null; 
                tx = HibernateTxMgr.beginTrans("Add a new relationships...");; 
                session = (Session); tx.getSession();; 
                parent = new ParentPO();; 
                ChildPO child = new ChildPO();; 
                ChildPO child2 = new ChildPO();; 
                List list = new ArrayList();; 
                list.add(child);; 
                list.add(child2);; 
                parent.setChildren(list);; 
                session.save(parent);; 
                session.flush();; 
                System.out.println("dddddddddddddddddddddddddddddddddddddddddddddddddddddd"); ; 
                ChildPO child3 = new ChildPO();; 
                child3.setParent(parent);; 
                session.save(child3);; 
                session.flush();; 
                System.out.println("eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"); ; 
                tx.endTrans();;

生成的SQL沒有變

Java代碼

Hibernate: insert into PARENT (ID); values (default);
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
dddddddddddddddddddddddddddddddddddddddddddddddddddddd
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

Hibernate: insert into PARENT (ID); values (default); 
 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
 
dddddddddddddddddddddddddddddddddddddddddddddddddddddd 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

*注意父子關係丟失了 C:/Myapp/SQLLIB/BIN>db2 select * from child

Java代碼

ID PARENTID
----------- -----------
74 -
75 -
76 45
C:/Myapp/SQLLIB/BIN>db2 select * from parent
ID
-----------
45

ID          PARENTID 
----------- ----------- 
         74           - 
         75           - 
         76          45 
C:/Myapp/SQLLIB/BIN>db2 select * from parent 
 
ID 
----------- 
         45

*爲什麼最後一個孩子的父親沒有丟失呢？就在於child3.setParent(parent);，所以關係是由孩子維護的，如果child不setParent，或者 new childPO(父親)的話父子關係就丟失了，parent.setChildren(list);是沒有用的！
*這裏就又引入了另外一個問題爲什麼要用inverse? 用了它維護關係起豈不是很麻煩？，這裏給出個例子給大家一個解釋：（關鍵原因在於性能）

下面這個例子和例子一完全一樣，所差的就是沒有用inverse=true

例子2：

Java代碼

hibernate-mapping>
<class name="com.etech.bm.po.ChildPO" table="CHILD">
<id name="id" column="ID" type="integer">
<generator class="identity"/>
</id>
<many-to-one name="parent" class="com.etech.bm.po.ParentPO" column="PARENTID"/>
</class>
<class name="com.etech.bm.po.ParentPO" table="PARENT">
<id name="id" column="ID" type="integer">
<generator class="identity"/>
</id>
<bag name="children" CASCADE=“ALL”>
<key column="PARENTID"/>
<one-to-many class="com.etech.bm.po.ChildPO"/>
</bag>
</class>
</hibernate-mapping>

hibernate-mapping> 
    <class name="com.etech.bm.po.ChildPO" table="CHILD"> 
                <id name="id" column="ID" type="integer"> 
                        <generator class="identity"/> 
                </id> 
        <many-to-one name="parent" class="com.etech.bm.po.ParentPO" column="PARENTID"/> 
    </class> 
    <class name="com.etech.bm.po.ParentPO" table="PARENT"> 
                <id name="id" column="ID" type="integer"> 
                        <generator class="identity"/> 
                </id> 
        <bag name="children"  CASCADE=“ALL”> 
                <key column="PARENTID"/> 
                <one-to-many class="com.etech.bm.po.ChildPO"/> 
        </bag> 
    </class> 
 
</hibernate-mapping>

Java代碼

drop table PARENT;
drop table CHILD;
create table PARENT (ID INTEGER not null generated by default as identity, primary key (ID););;
create table CHILD (ID INTEGER not null generated by default as identity, PARENTID INTEGER, primary key (ID););;
alter table CHILD add constraint FK3D1FCFC74B18345 foreign key (PARENTID); references PARENT;

drop table PARENT; 
drop table CHILD; 
create table PARENT (ID INTEGER not null generated by default as identity, primary key (ID););; 
create table CHILD (ID INTEGER not null generated by default as identity, PARENTID INTEGER, primary key (ID););; 
alter table CHILD add constraint FK3D1FCFC74B18345 foreign key (PARENTID); references PARENT;

Java代碼

ITxMgr tx = null;
tx = HibernateTxMgr.beginTrans("Add a new relationships...");;
session = (Session); tx.getSession();;
parent = new ParentPO();;
ChildPO child = new ChildPO(parent);;
ChildPO child2 = new ChildPO(parent);;
List list = new ArrayList();;
list.add(child);;
list.add(child2);;
parent.setChildren(list);;
session.save(parent);;
session.flush();;
System.out.println("dddddddddddddddddddddddddddddddddddddddddddddddddddddd"); ;
ChildPO child3 = new ChildPO();;
child3.setParent(parent);;
session.save(child3);;
session.flush();;
System.out.println("eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"); ;
tx.endTrans();;

ITxMgr tx = null; 
                tx = HibernateTxMgr.beginTrans("Add a new relationships...");; 
                session = (Session); tx.getSession();; 
                parent = new ParentPO();; 
                ChildPO child = new ChildPO(parent);; 
                ChildPO child2 = new ChildPO(parent);; 
                List list = new ArrayList();; 
                list.add(child);; 
                list.add(child2);; 
                parent.setChildren(list);; 
                session.save(parent);; 
                session.flush();; 
                System.out.println("dddddddddddddddddddddddddddddddddddddddddddddddddddddd"); ; 
                ChildPO child3 = new ChildPO();; 
                child3.setParent(parent);; 
                session.save(child3);; 
                session.flush();; 
                System.out.println("eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"); ; 
                tx.endTrans();;

hibernate 生成的sql Hibernate: insert into PARENT (ID) values (default)

Java代碼

Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
Hibernate: update CHILD set PARENTID=? where ID=?
dddddddddddddddddddddddddddddddddddddddddddddddddddddd
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
Hibernate: values IDENTITY_VAL_LOCAL();

Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
 
Hibernate: update CHILD set PARENTID=? where ID=? 
dddddddddddddddddddddddddddddddddddddddddddddddddddddd 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
Hibernate: values IDENTITY_VAL_LOCAL();

結果 C:/Myapp/SQLLIB/BIN>db2 select * from parent

Java代碼

ID
-----------
46
ID PARENTID
----------- -----------
77 46
78 46
79 46

ID 
----------- 
         46 
ID          PARENTID 
----------- ----------- 
         77          46 
         78          46 
         79          46

明顯比原來多了一句Hibernate: update CHILD set PARENTID=? where ID=?針對每一個孩子都去更新父親的id明顯速度很慢，因爲父親有個孩子的集合，他無法知道哪個孩子的父親id已經指向自己了,所以對於每一個孩子,都要更新父親使他只想自己，而這個關係由孩子維護就好多了，每個孩子只有一個父親，只有設置過的才需要更新，所以顯然，這個父子關係由孩子來維護比較省力.減輕了數據庫的負擔

*現在我們再來看看在沒有 inverse=true 的條件下 ChildPO child = new ChildPO(parent)---〉ChildPO child = new ChildPO()，

Java代碼

ITxMgr tx = null;
tx = HibernateTxMgr.beginTrans("Add a new relationships...");;
session = (Session); tx.getSession();;
parent = new ParentPO();;
ChildPO child = new ChildPO();;
ChildPO child2 = new ChildPO();;
List list = new ArrayList();;
list.add(child);;
list.add(child2);;
parent.setChildren(list);;
session.save(parent);;
session.flush();;
System.out.println("dddddddddddddddddddddddddddddddddddddddddddddddddddddd"); ;
ChildPO child3 = new ChildPO();;
child3.setParent(parent);;
session.save(child3);;
session.flush();;
System.out.println("eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"); ;
tx.endTrans();;

ITxMgr tx = null; 
                tx = HibernateTxMgr.beginTrans("Add a new relationships...");; 
                session = (Session); tx.getSession();; 
                parent = new ParentPO();; 
                ChildPO child = new ChildPO();; 
                ChildPO child2 = new ChildPO();; 
                List list = new ArrayList();; 
                list.add(child);; 
                list.add(child2);; 
                parent.setChildren(list);; 
                session.save(parent);; 
                session.flush();; 
                System.out.println("dddddddddddddddddddddddddddddddddddddddddddddddddddddd"); ; 
                ChildPO child3 = new ChildPO();; 
                child3.setParent(parent);; 
                session.save(child3);; 
                session.flush();; 
                System.out.println("eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee"); ; 
                tx.endTrans();;

生成的sql和結果和上面的是一樣的 hibernate 生成的sql Hibernate: insert into PARENT (ID) values (default)

Java代碼

Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
Hibernate: update CHILD set PARENTID=? where ID=?
dddddddddddddddddddddddddddddddddddddddddddddddddddddd
Hibernate: insert into CHILD (PARENTID, ID); values (?, default);
Hibernate: values IDENTITY_VAL_LOCAL();

Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
 
Hibernate: update CHILD set PARENTID=? where ID=? 
dddddddddddddddddddddddddddddddddddddddddddddddddddddd 
Hibernate: insert into CHILD (PARENTID, ID); values (?, default); 
Hibernate: values IDENTITY_VAL_LOCAL();

結果 C:/Myapp/SQLLIB/BIN>db2 select * from child

Java代碼

ID PARENTID
----------- -----------
83 48
84 48
85 48

ID          PARENTID 
----------- ----------- 
         83          48 
         84          48 
         85          48

C:/Myapp/SQLLIB/BIN>db2 select * from parent

Java代碼

ID
-----------
48

ID 
----------- 
         48

*顯然在沒有 inverse=true 的情況下，父子兩邊都維護父子關係所以只要有 parent.setchildren(),或者 child.setparent()兩者之一就可以了

對inverse=true的總結：不用inverse=ture,對開發者來說寫代碼比較方便，但是程序執行的效率比較低下，，用inverse=ture一定要注意，一定要對維護關係的一方進行調用，否則會有意想不到的破壞力。

wangzhuoyan

發佈了18 篇原創文章 · 獲贊 3 · 訪問量 16萬+

私信關注

Hibernate配置說明

80後的十三種最深寂寞(轉)

使用svn搭建服務器，客戶端使用

使用DOM4J操作xml

Struts2 action的擴展名兩種修改方法

Linux下安裝使用Subversion

Mac下配置sublime實現LaTeX

https://yachay.unat.edu.pe/blog/index.php?comment_area=format_blog&comment_component=blog&comment_co

linux以太網驅動總結