Mybatis学习（二）关联映射

1.一对一映射

（1）修改UserMapper.xml

<?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.xx.dao.UserDao">
    <resultMap id="UserResultMap" type="com.xx.entity.User">
        <id column="ID" property="id" jdbcType="DECIMAL"/>
        <result column="NAME" property="name" jdbcType="VARCHAR"/>
        <result column="SEX" property="sex" jdbcType="CHAR"/>
        <result column="AGE" property="age" jdbcType="DECIMAL"/>
　　　　　　<!--property指的是User类中定义的变量名称 column表示传入的参数 select指向select标签的id -->
        <association property="info" column="id" select="getTeacher"/>
    </resultMap>
<insert id ="addUser" parameterType="com.xx.entity.User">
    INSERT INTO TB_USER(ID,NAME,SEX,AGE) VALUES (#{id},#{name},#{sex},#{age})
</insert>

<select id="getTeacher" parameterType="int" resultType="com.xx.entity.StudentInfo">
    select * from STUDENTINFO t WHERE t.AGE = #{id}
</select>

 <select id="getUser" resultMap="UserResultMap">
     SELECT * FROM TB_USER
 </select>

</mapper>

　（2）添加StudentInfo.java

　（3）在User.java中实例化一个StudentInfo变量

2.一对多映射

（1）修改UserMapper.xml

<?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.xx.dao.UserDao">
    <resultMap id="UserResultMap" type="com.xx.entity.User">
        <id column="ID" property="id" jdbcType="DECIMAL"/>
        <result column="NAME" property="name" jdbcType="VARCHAR"/>
        <result column="SEX" property="sex" jdbcType="CHAR"/>
        <result column="AGE" property="age" jdbcType="DECIMAL"/>
　　　　<!-- fetchType表示懒加载 -->
        <collection property="info" column="id" select="getTeacher" javaType="ArrayList" ofType="com.xx.entity.StudentInfo" fetchType="lazy"/>
    </resultMap>
<insert id ="addUser" parameterType="com.xx.entity.User">
    INSERT INTO TB_USER(ID,NAME,SEX,AGE) VALUES (#{id},#{name},#{sex},#{age})
</insert>

<select id="getTeacher" parameterType="int" resultType="com.xx.entity.StudentInfo">
    select * from STUDENTINFO t WHERE t.AGE = #{id}
</select>

 <select id="getUser" resultMap="UserResultMap">
     SELECT * FROM TB_USER
 </select>
</mapper>

　（2）将一对一映射中实例化变量改为变量List,其余同上