本次的编程语言学习实例，有两张表，老师表teacher和班级表class，一个class班级对应一个teacher，一个teacher对应一个class，需求是根据班级id查询班级信息(带老师的信息)，希望对大家学习编程语言有所帮助。

创建teacher和class表：

CREATE TABLE teacher (

        t_id INT PRIMARY KEY AUTO_INCREMENT,

        t_name VARCHAR(20)

    );

    CREATE TABLE class (

        c_id INT PRIMARY KEY AUTO_INCREMENT,

        c_name VARCHAR(20),

        teacher_id INT

    );

    ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES

    teacher(t_id);

    INSERT INTO teacher(t_name) VALUES('LS1');

    INSERT INTO teacher(t_name) VALUES('LS2');

    INSERT INTO class(c_name, teacher_id) VALUES('bj_a', 1);

    INSERT INTO class(c_name, teacher_id) VALUES('bj_b', 2);

首先定义实体类

老师Teacher类

package mybatis.bean;

    public class Teacher {

        private int id;

        private String name;

        public Teacher() {

        }

        public Teacher(int id, String name) {

            super();

            this.id = id;

            this.name = name;

        }

        public int getId() {

            return id;

        }

        public void setId(int id) {

            this.id = id;

        }

        public String getName() {

            return name;

        }

        public void setName(String name) {

            this.name = name;

        }

        @Override

        public String toString() {

            return "Teacher [id=" + id + ", name=" + name + "]";

        }

}

班级Class类

package mybatis.bean;

public class Class {

    private int id;

    private String name;

    private Teacher teacher;

    public Class() {

    }

    public Class(int id, String name, Teacher teacher) {

        super();

        this.id = id;

        this.name = name;

        this.teacher = teacher;

    }

    public int getId() {

        return id;

    }

    public void setId(int id) {

        this.id = id;

    }

    public String getName() {

        return name;

    }

    public void setName(String name) {

        this.name = name;

    }

    public Teacher getTeacher() {

        return teacher;

    }

    public void setTeacher(Teacher teacher) {

        this.teacher = teacher;

    }

    @Override

    public String toString() {

        return "Class [id=" + id + ", name=" + name + ", teacher=" + teacher + "]";

    }

}

要实现一对一关联查询

SELECT * FROM class c, teacher t WHERE c.teacher_id = t.t_id AND c.c_id = 1;

classMapper.xml文件如下：

<!DOCTYPE mapper

    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"

    "//mybatis.org/dtd/mybatis-3-mapper.dtd">

        select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}

查询过程如下：

mybatis.bean.Class clazz = session.selectOne("mybatis.test5.classMapper.getClass", 1);

System.out.println(clazz);

控制台输出结果为：

Class [id=1, name=bj_a, teacher=Teacher [id=1, name=LS1]]

希望这篇文章可以帮助到你，总之同学们，IT资讯尽在职坐标。