mybatis的一对一，一对多的crud操作

一、一对一关联

 1.1、提出需求

　　根据班级id查询班级信息(带老师的信息)

1.2、创建表和数据

　　创建一张教师表和班级表，这里我们假设一个老师只负责教一个班，那么老师和班级之间的关系就是一种一对一的关系。

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('teacher1');INSERT INTO teacher(t_name) VALUES('teacher2');INSERT INTO class(c_name, teacher_id) VALUES('class_a', 1);INSERT INTO class(c_name, teacher_id) VALUES('class_b', 2);

表之间的关系如下：

1.3、定义实体类

　　1、Teacher类，Teacher类是teacher表对应的实体类。

package me.gacl.domain;/** * @author gacl * 定义teacher表对应的实体类 */public class Teacher {    //定义实体类的属性，与teacher表中的字段对应    private int id;            //id===>t_id    private String name;    //name===>t_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 + "]";    }}

　　2、Classes类，Classes类是class表对应的实体类

package me.gacl.domain;/** * @author gacl * 定义class表对应的实体类 */public class Classes {    //定义实体类的属性，与class表中的字段对应    private int id;            //id===>c_id    private String name;    //name===>c_name        /**     * class表中有一个teacher_id字段，所以在Classes类中定义一个teacher属性，     * 用于维护teacher和class之间的一对一关系，通过这个teacher属性就可以知道这个班级是由哪个老师负责的     */    private 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 "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher+ "]";    }}

1.4、定义sql映射文件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="com.lin.dao.ClassesMapper"><!-- 根据班级id查询班级信息(带老师的信息) ##1. 联表查询 SELECT * FROM class c,teacher t WHERE c.teacher_id=t.t_id AND c.c_id=1; ##2. 执行两次查询 SELECT * FROM class WHERE c_id=1; //teacher_id=1 SELECT * FROM teacher WHERE t_id=1;//使用上面得到的teacher_id --><!-- 方式一：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集 封装联表查询的数据(去除重复的数据) select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=1 --><select id="findById" parameterType="int" resultMap="ClassResultMap">select *from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}</select><!-- 使用resultMap映射实体类和字段之间的一一对应关系 --><resultMap type="com.lin.bean.Classes" id="ClassResultMap"><id property="id" column="c_id" /><result property="name" column="c_name" /><association property="teacher" javaType="com.lin.bean.Teacher"><id property="id" column="t_id" /><result property="name" column="t_name" /></association></resultMap><insert id="insertClass" parameterType="com.lin.bean.Classes"useGeneratedKeys="true" keyProperty="id">insert into class(c_name,teacher_id) value(#{name},#{teacher.id})</insert><select id="getTeacher" parameterType="int" resultType="com.lin.bean.Teacher">SELECTt_id id, t_name name FROM teacher WHERE t_id=#{id}</select><select id="getClass4" parameterType="int" resultMap="ClassResultMap">select * from class c, teacher t,student s where c.teacher_id=t.t_id and c.C_id=s.class_id and  c.c_id=#{id}</select></mapper>

在conf.xml文件中注册classMapper.xml

<mappers>        <!-- 注册classMapper.xml文件，         classMapper.xml位于me.gacl.mapping这个包下，所以resource写成me/gacl/mapping/classMapper.xml-->        <mapper resource="me/gacl/mapping/classMapper.xml"/></mappers>

1.5、编写工具MyBatisUtil

package com.lin.Util;import java.io.IOException;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 MyBatisUtil {  public static  SqlSession getSession() {SqlSessionFactory sessionFactory = null;String resource = "configuration.xml";try {sessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader(resource));} catch (IOException e) {// TODO Auto-generated catch blocke.printStackTrace();}return sessionFactory.openSession();}}

1.6、编写单元测试代码

package com.lin.test;import org.apache.ibatis.session.SqlSession;import org.junit.Test;import com.lin.Util.MyBatisUtil;import com.lin.bean.Classes;import com.lin.bean.Teacher;import com.lin.dao.ClassesMapper;public class MyTest {@Testpublic void testinstertClass() {SqlSession sqlSession = MyBatisUtil.getSession();ClassesMapper ClassesM = sqlSession.getMapper(ClassesMapper.class);Classes classes=new Classes();Teacher teacher=new Teacher();teacher.setId(2);teacher.setName("teacher1");classes.setName("linbany2");classes.setTeacher(teacher);ClassesM.insertClass(classes);sqlSession.commit();}@Testpublic void testGetClass2() {SqlSession sqlSession = MyBatisUtil.getSession();ClassesMapper ClassesM = sqlSession.getMapper(ClassesMapper.class);Classes clazz=ClassesM.findById(1);System.out.println(clazz);// 打印结果：Classes [id=1, name=class_a,sqlSession.commit();// teacher=Teacher [id=1, name=teacher1]]}}

1.7、MyBatis一对一关联查询总结

　　MyBatis中使用association标签来解决一对一的关联查询，association标签可用的属性如下：

• property:对象属性的名称
• javaType:对象属性的类型
• column:所对应的外键字段名称
• select:使用另一个查询封装的结果

二、一对多关联

2.1、提出需求

　　根据classId查询对应的班级信息,包括学生,老师

2.2、创建表和数据

　　在上面的一对一关联查询演示中，我们已经创建了班级表和教师表，因此这里再创建一张学生表

CREATE TABLE student(    s_id INT PRIMARY KEY AUTO_INCREMENT,     s_name VARCHAR(20),     class_id INT);INSERT INTO student(s_name, class_id) VALUES('student_A', 1);INSERT INTO student(s_name, class_id) VALUES('student_B', 1);INSERT INTO student(s_name, class_id) VALUES('student_C', 1);INSERT INTO student(s_name, class_id) VALUES('student_D', 2);INSERT INTO student(s_name, class_id) VALUES('student_E', 2);INSERT INTO student(s_name, class_id) VALUES('student_F', 2);

2.3、定义实体类

　　1、Student类

package me.gacl.domain;/** * @author gacl * 定义student表所对应的实体类 */public class Student {    //定义属性，和student表中的字段对应    private int id;            //id===>s_id    private String name;    //name===>s_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 "Student [id=" + id + ", name=" + name + "]";    }}

2、修改Classes类，添加一个List<Student> students属性，使用一个List<Student>集合属性表示班级拥有的学生，如下：

package me.gacl.domain;import java.util.List;/** * @author gacl * 定义class表对应的实体类 */public class Classes {    //定义实体类的属性，与class表中的字段对应    private int id;            //id===>c_id    private String name;    //name===>c_name        /**     * class表中有一个teacher_id字段，所以在Classes类中定义一个teacher属性，     * 用于维护teacher和class之间的一对一关系，通过这个teacher属性就可以知道这个班级是由哪个老师负责的     */    private Teacher teacher;    //使用一个List<Student>集合属性表示班级拥有的学生    private List<Student> students;    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;    }    public List<Student> getStudents() {        return students;    }    public void setStudents(List<Student> students) {        this.students = students;    }    @Override    public String toString() {        return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher                + ", students=" + students + "]";    }}

2.4、修改sql映射文件classMapper.xml

　　添加如下的SQL映射信息

<?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.lin.dao.ClassesMapper"><!-- 根据班级id查询班级信息(带老师的信息) ##1. 联表查询 SELECT * FROM class c,teacher t WHERE c.teacher_id=t.t_id AND c.c_id=1; ##2. 执行两次查询 SELECT * FROM class WHERE c_id=1; //teacher_id=1 SELECT * FROM teacher WHERE t_id=1;//使用上面得到的teacher_id --><!-- 方式一：嵌套结果：使用嵌套结果映射来处理重复的联合结果的子集 封装联表查询的数据(去除重复的数据) select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=1 --><select id="findById" parameterType="int" resultMap="ClassResultMap">select *from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id}</select><!-- 使用resultMap映射实体类和字段之间的一一对应关系 --><resultMap type="com.lin.bean.Classes" id="ClassResultMap"><id property="id" column="c_id" /><result property="name" column="c_name" /><association property="teacher" javaType="com.lin.bean.Teacher"><id property="id" column="t_id" /><result property="name" column="t_name" /></association><!-- ofType指定students集合中的对象类型 --><collection property="students" ofType="com.lin.bean.Student"><id property="id" column="s_id" /><result property="name" column="s_name" /></collection></resultMap><insert id="insertClass" parameterType="com.lin.bean.Classes"useGeneratedKeys="true" keyProperty="id">insert into class(c_name,teacher_id) value(#{name},#{teacher.id})</insert><select id="getTeacher" parameterType="int" resultType="com.lin.bean.Teacher">SELECTt_id id, t_name name FROM teacher WHERE t_id=#{id}</select><select id="getClass4" parameterType="int" resultMap="ClassResultMap">select * from class c, teacher t,student s where c.teacher_id=t.t_id and c.C_id=s.class_id and  c.c_id=#{id}</select></mapper>

2.5、编写单元测试代码

package com.lin.test;import org.apache.ibatis.session.SqlSession;import org.junit.Test;import com.lin.Util.MyBatisUtil;import com.lin.bean.Classes;import com.lin.bean.Teacher;import com.lin.dao.ClassesMapper;public class MyTest {@Testpublic void testinstertClass() {SqlSession sqlSession = MyBatisUtil.getSession();ClassesMapper ClassesM = sqlSession.getMapper(ClassesMapper.class);Classes classes=new Classes();Teacher teacher=new Teacher();teacher.setId(2);teacher.setName("teacher1");classes.setName("linbany2");classes.setTeacher(teacher);ClassesM.insertClass(classes);sqlSession.commit();}@Testpublic void testGetClass2() {SqlSession sqlSession = MyBatisUtil.getSession();ClassesMapper ClassesM = sqlSession.getMapper(ClassesMapper.class);Classes clazz=ClassesM.findById(1);System.out.println(clazz);// 打印结果：Classes [id=1, name=class_a,sqlSession.commit();// teacher=Teacher [id=1, name=teacher1]]}@Testpublic void testGetClass4(){SqlSession sqlSession = MyBatisUtil.getSession();ClassesMapper ClassesM = sqlSession.getMapper(ClassesMapper.class);Classes clazz=ClassesM.getClass4(1);System.out.print(clazz);sqlSession.commit();}}

  //打印结果：Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1], students=[Student [id=1, name=student_A], Student [id=2, name=student_B], Student [id=3, name=student_C]]]

2.6、MyBatis一对多关联查询总结

　　MyBatis中使用collection标签来解决一对多的关联查询，ofType属性指定集合中元素的对象类型。

参考博客：

http://www.cnblogs.com/xdp-gacl/p/4264440.html

http://www.cnblogs.com/liunanjava/p/4919752.html

源代码下载地址：

http://download.csdn.net/detail/linyeban/9724042