问如何在Hibernate中映射多对一关联，在Hibernate中，子对象具有组合键，其中一部分是父对象中的主键？

EN

table parent (
  parentid int (PK)
  ...
)

table child (
  parentid int (PK)
  childid int (PK)
  ...
)

<hibernate-mapping>
<class name="com.example.MyParent" table="parent">

    <id name="parentid" column="parentid" unsaved-value="0" >
        <generator class="identity"/>
    </id>

    <set name="children" cascade="all">
        <key>
            <column name="parentid"/>
        </key>
        <one-to-many class="com.example.MyChild" />
    </set>
...
</class>

<class name="com.example.MyChild" table="child">
    <composite-id name="id" class="com.example.MyChildId">
        <key-property name="parentid" column="parentid" />
        <key-property name="childid" column="childid" />
    </composite-id>
    ...
</class>

public void updateParent(MyParent param) {
    ht.saveOrUpdate(param);

}

DEBUG SQL - insert into Child(PARENTID, CHILDID) values (?, ?)
TRACE IntegerType - binding null to parameter: 1
TRACE IntegerType - binding '5678' to parameter: 2
WARN  JDBCExceptionReporter - SQL Error: -10, SQLState: 23502
ERROR JDBCExceptionReporter - integrity constraint violation: NOT NULL check constraint;     SYS_CT_10028 table: Child