mybatis 一对多-优快云博客

这篇博客介绍了MyBatis中的映射配置文件，包括如何获取一对一关联关系的数据。通过`TeacherOnetoMore`类和`Student`类展示了教师与学生的一对多关系，并在XML映射文件中定义了查询语句和结果映射。`resultMap`元素用于定义复杂的结果映射，包括`collection`属性来处理一对多关联，而`ofType`用于指定集合中元素的类型。

public class Student {
    private int id;
    private String name;

    private  int  tid;}

public class TeacherOnetoMore {
    private int id;
    private String name;

    private List<Student> students;}

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

    <select id="getTeacherOnetoMore" resultType="TeacherOnetoMore">
        select * from teacher;
    </select>


    <select id="getTeacherOnetoMoreById" resultMap="TeacherStudent">
        SELECT s.id sid,s.name sname,t.id tid,t.name tname
        FROM student s,teacher t
        where s.tid = t.id and t.id = #{id}
    </select>

    <resultMap id="TeacherStudent" type="TeacherOnetoMore">
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>
        <collection property="students" ofType="Student">
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>


    <select id="getTeacherOnetoMoreById2" resultMap="TeacherStudent2">
        select * from teacher where id = #{id}
    </select>

    <resultMap id="TeacherStudent2" type="TeacherOnetoMore">
        <collection property="students" column="id" javaType="ArrayList" ofType="Student" select="getStudentByTeacher"/>
    </resultMap>

    <select id="getStudentByTeacher" resultType="Student">
        select * from student where tid = #{id}
    </select>
</mapper>

javaType :用来指定实体类中属性的类型

ofType : 用来指定映射list或者集合中的pojo类型，泛型的约束类型；