JavaEE_09_Mybatis级联映射

最新推荐文章于 2025-06-19 19:13:16 发布

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最新推荐文章于 2025-06-19 19:13:16 发布

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文章标签： mybatis java-ee java spring intellij-idea spring boot tomcat

本文链接：https://blog.youkuaiyun.com/weixin_42788897/article/details/131211312

本文详细介绍了如何在Mybatis中实现对象关系的级联映射，包括对多（collection）和对一（association）操作。通过Teacher与Student实体类的关系，展示了在Mapper和XML配置文件中的映射设置，以及在Service和Controller层的调用方法，提供了一对多和一对多查询的完整示例。

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《Mybatis级联映射》

一、对象关系

表与表之间主要有四种关系：一对一，多对一，一对多，多对多。

Mybatis提供了两个标签实现这种关系：association（对一），collection（对多）。

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二、对多操作

com.hpr.entity.Teacher

...
public class Teacher {
    ...
        
    //一个老师对应多个学生
    private List<Student> students;

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }
}

com.hpr.mapper.TeacherMapper

...
public interface TeacherMapper {
    ...
    List<Teacher> testToMany();
}

mappers/TeacherMappper.xml

<!-- 外键结果映射 -->
<resultMap id="FkResultMap" type="com.hpr.entity.Teacher">
    <id column="teacher_id" property="teacherId"/>
    <result column="teacher_name" property="teacherName"/>
    <result column="age" property="age"/>
    <result column="phone_number" property="phoneNumber"/>
    <result column="info" property="info"/>
    <!-- 对多 -->
    <collection property="students" resultMap="com.hpr.mapper.StudentMapper.BaseResultMap"/>
</resultMap>

...

<!-- 测试一对多 -->
<select id="testToMany" resultMap="FkResultMap">
    select *
    from teacher t,
         student s
    where t.teacher_id = s.teacher_id
</select>

com.hpr.service.ITeacherService

...
public interface ITeacherService {
    ...
    Response<List<Teacher>> testToMany();

}

com.hpr.service.impl.TeacherService

public class TeacherService implements ITeacherService {

    @Override
    public Response<List<Teacher>> testToMany() {
        return new Response<>(200, "success", teacherMapper.testToMany());
    }
}

com.hpr.controller.MybatisController

...
public class MybatisController {
    ...
    @GetMapping("/testToMany")
    @ApiOperation("测试对多")
    public Response<List<Teacher>> testToMany() {
        return iTeacherService.testToMany();
    }
}

启动测试

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执行结果

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三、对一操作

com.hpr.entity.Student

...
public class Student {
    ...
        
    //一个学生对应一个老师
    private Teacher teacher;

    public Teacher getTeacher() {
        return teacher;
    }

    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }
}

com.hpr.mapper.StudentMapper

...
@Repository
public interface StudentMapper {
    ...
    List<Student> testToOne();
}

mappers/StudentMappper.xml

<!-- 外键结果映射 -->
<resultMap id="FkResultMap" type="com.hpr.entity.Student">
    <id column="student_id" property="studentId"/>
    <result column="student_name" property="studentName"/>
    <result column="chinese" property="chinese"/>
    <result column="math" property="math"/>
    <result column="english" property="english"/>
    <result column="teacher_id" property="teacherId"/>
    <!-- 对一 -->
    <association property="teacher" resultMap="com.hpr.mapper.TeacherMapper.BaseResultMap"/>
</resultMap>

...

<select id="testToOne" resultMap="FkResultMap">
    select *
    from student s,
         teacher t
    where s.teacher_id = t.teacher_id
</select>

com.hpr.service.IStudentService

...
public interface IStudentService {
    ...
    Response<List<Student>> testToOne();
}

com.hpr.service.impl.StudentService

...
@Service
public class StudentService implements IStudentService {

    @Autowired
    private StudentMapper studentMapper;

    ...
    @Override
    public Response<List<Student>> testToOne() {
        return new Response<>(200, "success", studentMapper.testToOne());
    }
}

com.hpr.controller.MybatisController

...
public class MybatisController {
    ...
    @GetMapping("/testToOne")
    @ApiOperation("测试对一")
    public Response<List<Student>> testToOne() {
        return iStudentService.testToOne();
    }
}