前段时间碰到这个问题，主要是hbm文件的的写法问题。我建了两个表，parent中的Pid与child中的Cid是一对多关系,Child中的cid与otherid只组合主键.如下
parent表
字段名
类型
长度
Pid (PK)
Character
10
Name
Character
10
Child表
字段名
类型
长度
cid (PK)
Character
10
Otherid (PK)
Smallint
Name
Character
10
hbm文件：
Parent.hbm.xml
<?xml version="1.0" encoding="GB2312"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping>
<class name="Parent" table="parent">
<id
name="pid"
column="pid"
type="string"
unsaved-value="any"
>
<generator class="assigned"/>
</id>
<property name="name"/>
<set name="children" cascade="all-delete-orphan" inverse="true" lazy="true" >
<key column="CID" />
<one-to-many class="Child"/>
</set>
</class>
</hibernate-mapping>
Child.hbm.xml
<?xml version="1.0" encoding="GB2312"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 2.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">
<hibernate-mapping>
<class name="Child" table="child">
<composite-id name="childpk" class="Childpk" unsaved-value="any">
<key-many-to-one name="parent" class="Parent" column="cid" />
<key-property name="otherid" column="otherid" type="integer"/>
</composite-id>
<many-to-one name="parent" class="Parent" column="CID" cascade="save-update" not-null="true" update="false" insert="false" />
<property name="name" column="name" type="string" />
</class>
</hibernate-mapping>
这两个hbm文件里面主要是：Parent中的<set name="children" cascade="all-delete-orphan" inverse="true" lazy="true" >
<key column="CID" />
<one-to-many class="Child"/>
</set> 和Child中的<many-to-one name="parent" class="Parent" column="CID" cascade="save-update" not-null="true" update="false" insert="false" />
这两个构成一对多关系中组合主键的双向关联。另外在写PO类的时候要注意hashcode和equals写的正确