An association from the table blog_friend refers to an unmapped class: User

数据库blog_friend只有外键，是为了实现添加好友功能的
blog_friend数据库为
create table blog_friends(
userid integer         references blog_user(id),
friendid integer         references blog_user(id),
);
在创建实体时并没有创建Friend类
User.hbm.xml为
<hibernate-mapping>
    <class name="User" table="blog_user" schema="dbo" catalog="blog">
        <id name="id" type="java.lang.Long">
            <column name="id" />
            <generator class="native"></generator>
        </id>
        <property name="username" type="java.lang.String">
            <column name="username" length="20" not-null="true" />
        </property>
        <property name="password" type="java.lang.String">
            <column name="password" length="20" not-null="true" />
        </property>
        <property name="question" type="java.lang.String">
            <column name="question" length="100" not-null="true" />
        </property>
        <property name="answer" type="java.lang.String">
            <column name="answer" length="100" not-null="true" />
        </property>
        <property name="useflag" type="java.lang.Integer">
            <column name="useflag" not-null="true" />
        </property>
        <property name="visitcount" type="java.lang.Long">
            <column name="visitcount" />
        </property>
        
        <set name="comments" inverse="true">
            <key>
                <column name="commentatorid" />
            </key>
            <one-to-many class="Comment" />
        </set>
        <set name="blogs" inverse="true">
            <key>
                <column name="userid" />
            </key>
            <one-to-many class="Blog" />
        </set>
        
        <set name="friends" table="blog_friend">
         <key>
         <column name="userid" />
         </key>     
         <many-to-many class="" entity-name="entity.User">
         <column name="friendid"></column>
         </many-to-many>   
        </set>
        <set name="friendToMes" table="blog_friend">
         <key>
         <column name="friendid" />
         </key>     
         <many-to-many class="" entity-name="entity.User">
         <column name="userid"></column>
         </many-to-many>   
        </set>
    </class>
</hibernate-mapping>
报错为An association from the table blog_friend refers to an unmapped class: entity.User
不知道哪位大侠能帮帮我！！