mybatis--一对一关联查询

(1)创建数据库mybatisonetoone

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)，

创建teacher和class表：

CREATE DATABASE mybatisonetoone;
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);

(2)创建config/config.xml文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>

<environments default="development">
	    <environment id="development">
		<transactionManager type="JDBC" />
		<dataSource type="POOLED">
		<property name="driver" value="com.mysql.jdbc.Driver" />
		<property name="url" value="jdbc:mysql://localhost:3306/mybatisonetoone"/>
		<property name="username" value="root"/>
		<property name="password" value="123456"/>
		</dataSource>
		</environment>
</environments>

<mappers>
	    <!-- // power by http://www.yiibai.com -->
	    <mapper resource="mybatis/bean/ClassMapper.xml" />
</mappers>
</configuration>

(3) 实现两个实体类Class.class和Teacher.class

Class.class

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 + "]";
    }
}

Teacher.java

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 + "]";
     }
}

(4) 然后配置ClassMapper.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="mybatis.bean.classMapper">
<!--根据id查询到一个班级信息（带老师信息） -->
<!-- 嵌套结果 -->
<!--   
<select id="getClass" parameterType="int" resultMap="ClassResultMap">
方式一
select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
</select>
<resultMap type="mybatis.bean.Class" id="ClassResultMap">
    <id property="id" column="c_id" />
    <result property="name" column="c_name" />
    <association property="teacher" column="teacher_id" javaType="mybatis.bean.Teacher">
    <id property="id" column="t_id" />
    <result property="name" column="t_name" />
</association>
</resultMap> -->
<!--嵌套查询  -->
<select id="getClass" parameterType="int" resultMap="ClassResultMap">
    select * from class where c_id=#{id}
</select>
<resultMap type="mybatis.bean.Class" id="ClassResultMap">
    <id property="id" column="c_id" />
    <result property="name" column="c_name" />
    <association property="teacher" column="teacher_id" javaType="mybatis.bean.Teacher" select="getTeacher">
    </association>
</resultMap>
<!-- 使用了sql别名  -->
<select id="getTeacher" parameterType="int" resultType="mybatis.bean.Teacher">
    SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id}
</select>
</mapper>

(5)最后配置Main.class执行查询操作

package Main;
import java.io.Reader;
import java.text.MessageFormat;
import java.util.List;

import mybatis.bean.Class;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class Main {
	private static SqlSessionFactory sqlSessionFactory;
	private static Reader reader;

	static {
		try {
			reader = Resources.getResourceAsReader("config/config.xml");
			sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

	public static SqlSessionFactory getSession() {
		return sqlSessionFactory;
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		SqlSession session = sqlSessionFactory.openSession();
		mybatis.bean.Class clazz = session.selectOne("mybatis.bean.classMapper.getClass", 2);
		System.out.println(clazz);
	}
}

执行Main函数后得出的程序结果如下：

程序结构图如下：