inverse的含义说得玄乎点是控制翻转，说得普通就是关系的维护有谁来做。
因为在关系数据库里面table和table之间是通过外键维护关系的(1-1,1-n)，对于1-n的情况,
很显然,外键由N的一方来维护比有1的一方来维护要好，这就是OOP中的has a的关系，
用hibernate进行数据存取的时候如果在集合属性里面不设置inverse=true,那么在保存n后，
hibernate会更新外键----update TEST.Groups set PARENT_ID=? where id=?(PARENT_ID
是外键)。然而这是多余的
Hibernate一对多双向关联及inverse的作用
在测试Hibernate的一对多双向关联映射时，碰到很有趣的问题，跟inverse属性直接相关。
1、People.hbm.xml
<
hibernate-mapping
default-lazy
="false"
>
<
class
name
="com.persistent.People"
table
="people"
>
<
id
name
="id"
column
="peopleId"
unsaved-value
="0"
>
<
generator
class
="increment"
>
</
generator
>
</
id
>
<
property
name
="name"
column
="name"
></
property
>
<
set
name
="addresses"
cascade
="save-update"
>
<
key
column
="peopleId"
not-null
="true"
/>
<
one-to-many
class
="com.persistent.Address"
/>
</
set
>
</
class
>
</
hibernate-mapping
>
2、Address.hbm.xml
<
hibernate-mapping
>
<
class
name
="com.persistent.Address"
table
="address"
>
<
id
name
="id"
column
="addressId"
unsaved-value
="0"
>
<
generator
class
="increment"
>
</
generator
>
</
id
>
<
many-to-one
name
="people"
column
="peopleId"
insert
="false"
update
="false"
></
many-to-one
>
<
property
name
="addressName"
column
="addressName"
></
property
>
<
property
name
="codeNumber"
column
="codeNumber"
></
property
>
</
class
>
</
hibernate-mapping
>
3、People.java和Address.java
public
class
People
{ 
private long id; private String name; private Set addresses = new HashSet(); ...
}
public
class
Address
{ private long id; private People people; private String addressName; private String codeNumber; ...}
4、数据库结构
people表：{peopleId,name}
address表：{addressId,peopleId,addressName,codeNumber}
5、测试代码
People people
=
new
People();people.setName(
"linda
"
);Address address
=
new
Address();address.setAddressName(
"yunnan
"
);address.setCodeNumber(
"
564123
"
);address.setPeople(people);people.getAddresses().add(address);Session session
=
HibernateSessionFactory.getSession();session.beginTransaction();session.save(people);session.getTransaction().commit();
6、运行结果
上面测试代码运行起来正确：
Hibernate: select max(peopleId) from people
Hibernate: select max(addressId) from address
Hibernate: insert into people (name, peopleId) values (?, ?)
Hibernate: insert into address (addressName, codeNumber, peopleId, addressId) values (?, ?, ?, ?)
Hibernate: update address set peopleId=? where addressId=?
如果将People.hbm.xml映射改写一下：
<
set
name
="addresses"
cascade
="save-update"
inverse
="true"
>
<
key
column
="peopleId"
not-null
="true"
/>
<
one-to-many
class
="com.persistent.Address"
/>
</
set
>
不同之处在于添加了inverse="true"，结果：
Hibernate: select max(peopleId) from people
Hibernate: select max(addressId) from address
Hibernate: insert into people (name, peopleId) values (?, ?)
Hibernate: insert into address (addressName, codeNumber, addressId) values (?, ?, ?)
可以看到，peopleId并没有写入到关联的address当中，数据库address表中相应记录的peopleId字段为空。
7、分析
在Hibernate中，术语inverse是反转的意思，在关联关系中，inverse="false"为主控方，由主控方负责维护对象的关联关系。所以上面的映射文件改动之后，address为主控方，people为被控方，但是测试代码只进行了一个保存操作session.save(people)，这是针对people的，因此无法正确级联保存address。而原来的映射文件中（虽然没有明确指明，Hibernate默认inverse="false"），people为主控方，因此保存people时它会保证关联的address的正确保存。
也就是说，Hibernate仅仅按照主控方对象的状态的变化来同步更新数据库。按照原来的映射文件，people.getAddresses().add(address)，即主控方对象的状态发生了改变，因此数据库会跟着对象状态的变化来同步更新数据库；而address.setPeople(people)，即被控方对象的状态发生了改变，它是不能触发对象和数据库的同步更新的。