有关hibernate配置文件的疑问?
1 <hibernate-mapping>
2 <class name="GuestBook" table="GuestBook" lazy="true">
3 <id name="id" type="integer" unsaved-value="null">
4 <column name="id" sql-type="int" not-null="true"/>
5 <generator class="identity"/>
6 </id>
7 <property name="author" column="author" not-null="true" unique="false"/>
8 </class>
9 </hibernate-mapping>
2的lazy="tru"是什么意思,第3行unsaved-value="null"又是什么意思?