Hibernate的SaveOrUpdate方法和unsave-value参数
unsaved-value:
如果取到的Id值和hbm映射文件中指定的 unsave-value相等,那么Hibernate认为child是新的内存临时对象,发送save,如果不相等,那么Hibernate认为child是已经持久过的对象,发送update
saveOrUpdate :
hibernate首先会根据id查询数据库，如果有记录则进行update，如果没有，则进行insert
假设我们的Customer对应的数据库中已经有了以下三条数据
insert into customer values("1","john");
insert into customer values("2","marry");
insert into customer values("3","cathy");
我们的数据库操作这样写：
public
void
saveCustomer(Customer customer)
...
{
getHibernateTemplate().saveOrUpdate(customer); 
}
如果我们不使用unsaved-value属性，则unsaved-value默认为null,也就是说我们新建一个customer对象，如果其id为空，则进行插入，如果不为空，则进行更新，这符合逻辑（id策略为assigened除外，因为必须手动设置id）
Customer.hbm.xml
<?
xml version
=
"
1.0
"
encoding
=
"
utf-8
"
?>
<!
DOCTYPE hibernate
-
mapping PUBLIC
"
-//Hibernate/Hibernate Mapping DTD 3.0//EN
"
"
http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd
"
>
<!--
Mapping file autogenerated by MyEclipse Persistence Tools
-->
<
hibernate
-
mapping
>
<
class
name
=
"
ch9.SimpleOneToMany.Customer
"
table
=
"
customer
"
catalog
=
"
spring
"
>
<
id name
=
"
id
"
type
=
"
java.lang.String
"
>
<
column name
=
"
id
"
length
=
"
10
"
/>
<
generator
class
=
"
assigned
"
/>
</
id
>
<
property name
=
"
name
"
type
=
"
java.lang.String
"
>
<
column name
=
"
name
"
length
=
"
10
"
/>
</
property
>
<
set name
=
"
addresses
"
inverse
=
"
true
"
lazy
=
"
false
"
>
<
key
>
<
column name
=
"
customerid
"
length
=
"
10
"
/>
</
key
>
<
one
-
to
-
many
class
=
"
ch9.SimpleOneToMany.Address
"
/>
</
set
>
</
class
>
</
hibernate
-
mapping
>
我们首先不设置Unsaved-value
测试代码：
Customer c=new Customer("0","gaoxiang",null);
testDAOImpl.saveCustomer(c);
结果：
Hibernate: select customer_.id, customer_.name as name1_ from spring.customer customer_ where customer_.id=?
Hibernate: insert into spring.customer (name, id) values (?, ?)
可以看到，hiberante首先根绝指定id="0"查询，如果没有查询到，则进行插入
我们再执行一边测试代码，并修改一下属性为gaoxiang1：
Hibernate: select customer_.id, customer_.name as name1_ from spring.customer customer_ where customer_.id=?
Hibernate: update spring.customer set name=? where id=?
这时候就进行update操作了
下面，我们在看看设置了unsaved-value=0的情况，这就是说，只有当id为0的时候才进行新增，其余都进行修改
运行测试
Customer c=new Customer("0","gaoxiang",null);
testDAOImpl.saveCustomer(c);
结果如下
Hibernate: insert into spring.customer (name, id) values (?, ?)
可以看到hibernate不会首先去检查，而是在id=unsaved-value的时候直接执行insert
改变测试代码为修改一个已经有的记录：
Customer c=new Customer("1","gaoxiang1",null);
testDAOImpl.saveCustomer(c);
结果如下：Hibernate: update spring.customer set name=? where id=? hibernate直接进行update
如果设置的unsaved-value,如果给定一个不存在的id如下：
Customer c=new Customer("100","gaoxiang1",null);
testDAOImpl.saveCustomer(c);
则hibernate还是会直接去执行update,虽然后台使用的是saveOrUpdate方法