Hibernate org.hibernate.AssertionFailure：null identifier

Question

当实体保存时，抛出与实体ID相关的错误。我试图将XML映射中的生成器类更改为本机，但在这种情况下，Hibernate根本不保存实体。

我使用PostgreSQL。

org.hibernate.AssertionFailure: null identifier
    org.hibernate.engine.spi.EntityKey.<init>(EntityKey.java:69)
    org.hibernate.internal.AbstractSessionImpl.generateEntityKey(AbstractSessionImpl.java:240)
    org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:306)

这是我的XML mappaing。

<hibernate-mapping>
<class name="com.mello.core.domain.model.board.Board" table="board">

    <id name="id" type="java.lang.Long" column="id">
        <generator class="identity"/>
    </id>

    <many-to-one name="profile" cascade="merge" column="id_profile"
                 class="com.mello.core.domain.model.account.Profile" unique="true"/>

    <property name="name" column="board_name" type="java.lang.String"/>
    <property name="description" column="description" type="java.lang.String"/>
    <property name="important" column="important" type="java.lang.Boolean"/>

</class>

<hibernate-mapping>
<joined-subclass name="com.mello.core.domain.model.account.Profile" extends="com.mello.core.domain.model.account.User"
                 table="profile">
    <key column="fk_user_id"/>

    <bag name="friends" lazy="false" table="friend"
         cascade="all" inverse="false" fetch="select">
        <key>
            <column name="id" not-null="false"/>
        </key>
        <many-to-many entity-name="com.mello.core.domain.model.account.Profile">
            <column name="friend_id"/>
        </many-to-many>
    </bag>

</joined-subclass>

public boolean save(Board board) {
    Session session = HibernateUtil.getSession(sessionFactory);
    session.beginTransaction();
    try {
        session.merge(board);
        session.getTransaction().commit();
    } catch (Exception e) {
        session.getTransaction().rollback();
        throw new RepositoryException(e);
    } finally {
        HibernateUtil.closeSession(session);
    }
    return true;
}