【Mybatis学习笔记】系列之二：Mybatis双项一对多关联

条件：Group和Student是一对多关系

一：GroupMapper.xml内容如下

<?xml version="1.0" encoding="UTF-8" ?>  <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">  <mapper namespace="com.company.dao.IGroupDAO"> 

    <resultMap type="Group" id="groupResultMap" >          <id column="g_id" property="id"/>          <result column="g_name" property="name"/>          <result column="g_position" property="position"/>      </resultMap>      <sql id="getALl">select * from</sql>            <!-- 意图想通过获得组和组中的所有student,此处相当于one2many -->      <resultMap type="Group" id="getGroupAndStudents">          <id column="g_id" property="id"/>          <result column="g_name" property="name"/>          <result column="g_position" property="position"/>          <collection property="students" ofType="Student" column="group_id"><!-- 注意此处的group_id是student表的外键 -->              <id column="id" property="id"/>              <result column="name" property="name"/>              <result column="birth" property="birth"/>          </collection>      </resultMap>            <select id="getById" parameterType="int" resultMap="getGroupAndStudents">          select g.g_id,g.g_name,g.g_position,s.id,s.name,s.birth ,s.group_id          from g_group g          left join student s on g.g_id = s.group_id          where g.g_id = #{id}      </select>        <select id="getByIdResultMap" parameterType="_int" resultMap="groupResultMap">          select g_id ,g_name, g_position  from g_group where g_id=#{id}      </select>      <delete id="deleteById" parameterType="_int" timeout="1000">          delete from g_group where g_id=#{id}      </delete>      <insert id="add" parameterType="Group">          insert into g_group(g_id, g_name, g_position)           values(#{id}, #{name}, #{position})      </insert>        </mapper>  

二：StudentMapper.xml内容如下

<?xml version="1.0" encoding="UTF-8" ?>  <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">  <mapper namespace="com.company.dao.IStudentDAO">            <!-- mybatis缓存 -->      <cache eviction="LRU" flushInterval="600000" size="1024" readOnly="false" />            <!-- sql标签用来定义一些可以被重用的sql语句或字段或片段等 -->      <sql id="studentColumns">select id,name,birth from student</sql>            <!-- 此处获得多对一的关系 ,但就单条记录而言却是一对一的关系，所以一对一的写法跟此相同-->      <resultMap type="Student" id="getStudentAndGroup" >          <id column="id" property="id"/>          <result column="name" property="name"/>          <result column="birth" property="birth"/>          <association property="group" column="group_id" javaType="Group">              <id column="g_id" property="id"/>              <result column="g_name" property="name"/>              <result column="g_position" property="position"/>          </association>      </resultMap>      <select id="many2one" resultMap="getStudentAndGroup" parameterType="int" >          select s.id,s.name,s.birth,s.group_id,g.g_id,g.g_name,g.g_position           from student s           left join g_group g on s.group_id = g.g_id          where s.id = #{id}      </select>                  <!-- 意图是获得一个学生，并且获得该学生所属的组，跟上面的意思差不多 ,用association的select属性-->      <!-- 于上面的相比个人感觉上面的效率要高些，因为上面只有一条sql语句 -->      <resultMap type="Student" id="getStudentAndGroupUseSelectMap">          <id column="id" property="id"/>          <result column="name" property="name"/>          <result column="birth" property="birth"/>          <association property="group" column="group_id" javaType="Group" select="selectGroup" />      </resultMap>      <select id="getStudentAndGroupUseSelect" resultMap="getStudentAndGroupUseSelectMap" parameterType="int">          select *           from student           where id = #{id}      </select>      <select id="selectGroup" resultType="Group" parameterType="int" flushCache="false" useCache="true"><!-- 此处实用缓存 -->          select g_id as id, g_name as name, g_position as position           from g_group           where g_id = #{id}      </select>        <!-- 动态sql语句 的测试dynamic sql-->          <select id="getStudentBySomeCondition" parameterType="Student" resultType="Student">          select *          from student          <where>              <if test="id != null">                  id>2              </if>              <if test="name != null">                  and name like '%g%'              </if>          </where>      </select>            <!-- MyBatis调用存储过程 -->      <resultMap type="Student" id="studentMap">          <id column="id" property="id"/>          <result column="name" property="name"/>          <result column="birth" property="birth"/>      </resultMap>      <select id="getAllUser" statementType="CALLABLE" >          {call get_all_student(#{students ,mode=OUT, jdbcType=CURSOR, javaType=ResultSet, resultMap=studentMap} )}      </select>                  <!-- MyBatis向student表中插入一条数据 -->      <insert id="add" parameterType="Student" keyColumn="id">          <selectKey keyProperty="id" order="BEFORE" resultType="int">               select stu_id_sequence.nextval from dual          </selectKey>          insert into student(id,name,birth) values(#{id},#{name},#{birth})      </insert>            <!-- 根据id获得学生的信息 -->      <select id="getById" parameterType="int" resultType="Student">          <include refid="studentColumns"/> where id=#{id}      </select>            <!-- 此处的实现方法是一个分页的原型,请查看IStudentDAOImpl.java中的调用方法 -->      <select id="getAllStudent" resultMap="studentMap">          <include refid="studentColumns"/> order by id<!--此处是引用了上面预定义好的sql语句-->      </select>              </mapper>