对数据库与mybatis的总结

#{}是预编译处理，${}是字符串替换。
使用#{}可以有效的防止SQL注入，提高系统安全性。
mybatis的一对多与多对一：

<mapper namespace="com.lcb.mapping.userMapper">  
<!--association  一对一关联查询 -->  
<select id="getClass" parameterType="int" resultMap="ClassesResultMap">  
    select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id}  
</select>  

<resultMap type="com.lcb.user.Classes" id="ClassesResultMap">  
    <!-- 实体类的字段名和数据表的字段名映射 -->  
    <id property="id" column="c_id"/>  
    <result property="name" column="c_name"/>  
    <association property="teacher" javaType="com.lcb.user.Teacher">  
        <id property="id" column="t_id"/>  
        <result property="name" column="t_name"/>  
    </association>  
</resultMap>  


<!--collection  一对多关联查询 -->  
<select id="getClass2" parameterType="int" resultMap="ClassesResultMap2">  
    select * from class c,teacher t,student s where c.teacher_id=t.t_id and c.c_id=s.class_id and c.c_id=#{id}  
</select>  

<resultMap type="com.lcb.user.Classes" id="ClassesResultMap2">  
    <id property="id" column="c_id"/>  
    <result property="name" column="c_name"/>  
    <association property="teacher" javaType="com.lcb.user.Teacher">  
        <id property="id" column="t_id"/>  
        <result property="name" column="t_name"/>  
    </association>  

    <collection property="student" ofType="com.lcb.user.Student">  
        <id property="id" column="s_id"/>  
        <result property="name" column="s_name"/>  
    </collection>  
</resultMap>  
</mapper>