MyBatis 详解（一对一，一对多，多对多）

1、什么是MyBatis?

MyBatis 本是apache的一个开源项目iBatis, 2010年这个项目由apache software foundation 迁移到了google code，并且改名为MyBatis 。2013年11月迁移到Github。
iBATIS一词来源于“internet”和“abatis”的组合，是一个基于Java的持久层框架。iBATIS提供的持久层框架包括SQL Maps和Data Access Objects（DAO）。
MyBatis 是支持普通 SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis 消除了几乎所有的JDBC代码和参数的手工设置以及结果集的检索。MyBatis 使用简单的 XML或注解用于配置和原始映射，将接口和 Java 的POJOs（Plain Ordinary Java Objects，普通的 Java对象）映射成数据库中的记录。

2、MyBatis 入门实例基于xml配置

①、创建MySQL数据库：mybatisDemo和表：person

create database mybatisDemo;
use mybatisDemo;
create table person(pid int primary key AUTO_INCREMENT, pname varchar(50), page int);

②、建立一个Java工程，并导入相应的jar包

③、在 MyBatisDemo 工程中添加数据库配置文件 mybatis-configuration.xml

<?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>
<!-- 可以配置多个运行环境，但是每个 SqlSessionFactory 实例只能选择一个运行环境  
  一、development:开发模式
   二、work：工作模式-->
 <environments default="development">
 <!--id属性必须和上面的default一样  -->
    <environment id="development">
    <!--事务管理器
        一、JDBC：这个配置直接简单使用了 JDBC 的提交和回滚设置。它依赖于从数据源得到的连接来管理事务范围
        二、MANAGED：这个配置几乎没做什么。它从来不提交或回滚一个连接。而它会让容器来管理事务的整个生命周期
            比如 spring 或 JEE 应用服务器的上下文，默认情况下，它会关闭连接。然而一些容器并不希望这样，
            因此如果你需要从连接中停止它，就可以将 closeConnection 属性设置为 false，比如：
            <transactionManager type="MANAGED">
                <property name="closeConnection" value="false"/>
            </transactionManager>
      -->
      <transactionManager type="JDBC"/>
      <!--dataSource 元素使用标准的 JDBC 数据源接口来配置 JDBC 连接对象源  -->
      <dataSource type="POOLED">
        <property name="driver" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/mybatisdemo"/>
        <property name="username" value="root"/>
        <property name="password" value="root"/>
      </dataSource>
    </environment>
  </environments>
</configuration>

④、定义表所对应的实体类

package com.ys.bean;
 
public class Person {
    private int pid;
    private String pname;
    private int page;
     
    public int getPid() {
        return pid;
    }
    public void setPid(int pid) {
        this.pid = pid;
    }
    public String getPname() {
        return pname;
    }
    public void setPname(String pname) {
        this.pname = pname;
    }
    public int getPage() {
        return page;
    }
    public void setPage(int page) {
        this.page = page;
    }
    @Override
    public String toString() {
        return "Person [pid=" + pid + ", pname=" + pname + ", page=" + page
                + "]";
    }
}

⑤、定义操作 person 表的sql映射文件personMapper.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.ys.bean.personMapper">
  <!-- 根据 pid 查询 person 表中的数据
       id:唯一标识符，此文件中的id值不能重复
       resultType:返回值类型，一条数据库记录也就对应实体类的一个对象
       parameterType:参数类型，也就是查询条件的类型
   -->
  <select id="selectPersonById"
            resultType="com.ys.bean.Person" parameterType="int">
    <!-- 这里和普通的sql 查询语句差不多，对于只有一个查询条件后面的 #{pid}表示占位符，里面不一定要写pid,写啥都可以，但是不要空着；如果有多个查询条件，则要写pojo类里面的属性 -->
    select * from person where pid = #{pid}
  </select>
   
  <!-- 查询person 表所有数据 -->
  <select id="getAllPerson" resultType="com.ys.bean.Person">
    select * from person
  </select>
   
  <!-- 根据id更新数据 -->
  <update id="updatePersonById" parameterType="com.ys.bean.Person">
    update person set pname=#{pname},page=#{page} where pid = #{pid}
  </update>
   
  <!-- 向 person 表插入一条数据 -->
  <insert id="addPerson" parameterType="com.ys.bean.Person">
    insert into person(pid,pname,page) values(#{pid},#{pname},#{page})
  </insert>
   
  <!-- 根据 pid 删除数据 -->
  <delete id="deletePersonById" parameterType="Long">
    delete from person where pid=#{pid}
  </delete>
   
</mapper>

⑥、向 mybatis-configuration.xml 配置文件中注册 personMapper.xml 文件

<mappers>
       <!-- 注册personMapper.xml文件，
       personMapper.xml位于com.ys.bean这个包下，所以resource写成com/ys/bean/personMapper.xml-->
       <mapper resource="com/ys/bean/personMapper.xml"/>
</mappers>

⑦、创建测试类

package com.ys.test;
 
import java.io.InputStream;
import java.util.List;
 
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
 
import com.ys.bean.Person;
 
public class MyBatisTest {
    SqlSession session;
     
    @Before
    public void beforeLoadXML(){
        //加载 mybatis 配置文件
        InputStream inputStream = MyBatisTest.class.
                getClassLoader().getResourceAsStream("mybatis-configuration.xml");
        //构建sqlSession的工厂
        SqlSessionFactory sqlSessionFactory =
                new SqlSessionFactoryBuilder().build(inputStream);
        //根据 sqlSessionFactory 产生 session
        session = sqlSessionFactory.openSession();
    }
     
    //根据 pid 查询 person 表中的数据
    @Test
    public void testSelectById(){
        //这个字符串有 personMapper.xml 文件中 两个部分构成
        //<mapper namespace="com.ys.bean.personMapper"> 的 namespace 的值
        //<select id="selectPersonById" > id 值
        String statement = "com.ys.bean.personMapper"+".selectPersonById";
        Person p = session.selectOne(statement, 1);
        System.out.println(p);
        session.close();
    }
     
    //查询person 表所有数据
    @Test
    public void testGetAllPerson(){
        String statement = "com.ys.bean.personMapper.getAllPerson";
        List<Person> listPerson = session.selectList(statement);
        System.out.println(listPerson);
        session.close();
    }
     
    //根据id更新数据
    @Test
    public void updateById(){
        String statement = "com.ys.bean.personMapper.updatePersonById";
        Person p = new Person();
        p.setPid(1);
        p.setPname("aaa");
        p.setPage(11);
        session.update(statement, p);
        session.commit();
        session.close();
    }
     
    //向 person 表插入一条数据
    @Test
    public void addPerson(){
        String statement = "com.ys.bean.personMapper.addPerson";
        Person p = new Person();
        //由于我们设置了主键的自增长机制，故这里不需要手动设置 pid 的值
        //p.setPid(1);
        p.setPname("add");
        p.setPage(11);
        session.insert(statement, p);
        session.commit();
        session.close();
    }
     
    //根据 pid 删除person 表中的数据
    @Test
    public void deletePersonById(){
        String statement = "com.ys.bean.personMapper.deletePersonById";
        session.delete(statement, 1);
        session.commit();
        session.close();
         
    }
}

3、MyBatis 入门实例注解配置

①、上面的前面四步都是一样的，但是第五步不一样，我们不需要创建 personMapper.xml 文件，首先在 src 目录下创建 personMapper.java 文件

package com.ys.annocation;
 
import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;
 
import com.ys.bean.Person;
 
public interface PersonMapper {
     
    @Insert("insert into person(pid,pname,page) values(#{pid},#{pname},#{page})")
    public int add(Person person);
     
    @Select("select * from person where pid = #{pid}")
    public Person getPerson(int pid);
     
    @Update("update person set pname=#{pname},page=#{page} where pid = #{pid}")
    public int updatePerson(Person preson);
     
    @Delete("delete from person where pid=#{pid}")
    public int deletePerson(int pid);
 
}

②、向 mybatis-configuration.xml 配置文件中注册 personMapper.xml 文件

③、编写测试类

@Test
public void testAnnocation(){
    PersonMapper mapper = session.getMapper(PersonMapper.class);
    Person p = new Person();
    p.setPid(7);
    p.setPname("abc");
    p.setPage(11);
    //调用增加方法
    mapper.add(p);
    //调用查询方法
    Person p1 = mapper.getPerson(3);
    System.out.println(p1);
    //调用更新方法
    p.setPage(100);
    mapper.updatePerson(p);
    //调用删除方法
    mapper.deletePerson(7);
    session.commit();
    session.close();
}

4、MyBatis 入门实例 一对一 基于xml配置

这里我们以老师和班级为例，假设一般班级只能拥有有一个老师，一个老师只能带一个班级。

①、创建实体类

Teacher.java

package one.to.one;

public class Teacher {
private int tid;
private String tname;
private Classes classes;

public int getTid() {
    return tid;
}
public void setTid(int tid) {
    this.tid = tid;
}
public String getTname() {
    return tname;
}
public void setTname(String tname) {
    this.tname = tname;
}
public Classes getClasses() {
    return classes;
}
public void setClasses(Classes classes) {
    this.classes = classes;
}
@Override
public String toString() {
    return "Teacher [tid=" + tid + ", tname=" + tname + ", classes=" + classes + "]";
}

}

Classes.java

package one.to.one;
 
public class Classes {
    private int cid;
    private String cname;
    private Teacher teacher;
     
    public int getCid() {
        return cid;
    }
    public void setCid(int cid) {
        this.cid = cid;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public Teacher getTeacher() {
        return teacher;
    }
    public void setTeacher(Teacher teacher) {
        this.teacher = teacher;
    }
    @Override
    public String toString() {
        return "Classes [cid=" + cid + ", cname=" + cname + ", teacher=" + teacher + "]";
    }
     
}

②、在数据库中根据实体类创建相应的数据表

③、定义操作 Classes 表的sql映射文件classesMapper.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="one.to.one.classesMapper">
    <!--
         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 classes c, teacher t where c.tid=t.tid and c.tid=#{tid}
     -->
    <select id="getClasses" resultMap="getClassesMap" parameterType="int">
        select * from classes c ,teacher t
            where c.tid=t.tid and c.tid=#{tid}
    </select>
    <resultMap type="one.to.one.Classes" id="getClassesMap">
        <id column="cid" property="cid"/>
        <result column="cname" property="cname"/>
        <association property="teacher" javaType="one.to.one.Teacher">
            <id column="tid" property="tid"></id>
            <result column="tname" property="tname"/>
        </association>
    </resultMap>
    <!--
         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 teacher t,classes c where t.cid = c.cid and t.cid=#{cid}
     -->
    <select id="getTeacher" resultMap="getTeacherMap" parameterType="int">
        select * from teacher t,classes c
            where t.cid = c.cid and t.cid=#{cid}
    </select>
    <resultMap type="one.to.one.Teacher" id="getTeacherMap">
        <id column="tid" property="tid"/>
        <result column="tname" property="tname"/>
        <association property="classes" javaType="one.to.one.Classes">
            <id column="cid" property="cid"/>
            <result column="cname" property="cname"/>
        </association>
    </resultMap>
     
     
    <!--
         方式二：嵌套查询：通过执行另外一个SQL映射语句来返回预期的复杂类型
         SELECT * FROM classes WHERE cid=1;
         SELECT * FROM teacher WHERE tid=1   //1 是上一个查询得到的tid的值
         property:别名(属性名)    column：列名 -->
          <!-- 把teacher的字段设置进去 -->
    <select id="getClasses2" resultMap="getClassesMap2">
        select * from classes c where c.cid = #{cid}
    </select>
    <resultMap type="one.to.one.Classes" id="getClassesMap2">
        <id column="cid" property="cid"/>
        <result column="cname" property="cname"/>
        <collection property="teacher" column="tid" select="getTeacherCollection">
        </collection>
    </resultMap>
    <select id="getTeacherCollection" resultType="one.to.one.Teacher">
        select tid tid,tname tname from teacher where tid=#{tid}
    </select>
   
</mapper>

　说明：我们这里一对一的关联操作，有两种方式：

　　　　1、使用嵌套结果映射来处理重复的联合结果的子集

　　　　2、通过执行另外一个SQL映射语句来返回预期的复杂类型

　　　　相关属性解释：

④、向 mybatis-configuration.xml 配置文件中注册 classesMapper.xml 文件

⑤、编写测试类

package one.to.one;
 
import java.io.InputStream;
 
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
 
import com.ys.test.MyBatisTest;
 
public class OneToOneTest {
SqlSession session;
     
    @Before
    public void beforeLoadXML(){
        //加载 mybatis 配置文件
        InputStream inputStream = MyBatisTest.class.
                getClassLoader().getResourceAsStream("mybatis-configuration.xml");
        //构建sqlSession的工厂
        SqlSessionFactory sqlSessionFactory =
                new SqlSessionFactoryBuilder().build(inputStream);
        //根据 sqlSessionFactory 产生 session
        session = sqlSessionFactory.openSession();
    }
     
    //一对一嵌套结果方式：根据教师id查询班级信息
    @Test
    public void testGetClasses(){
        String statement = "one.to.one.classesMapper.getClasses";
        Classes c = session.selectOne(statement, 1);
        System.out.println(c);
    }
     
    //一对一嵌套结果方式：根据班级id查询教师信息
    @Test
    public void testGetTeacher(){
        String statement = "one.to.one.classesMapper.getTeacher";
        Teacher t = session.selectOne(statement, 1);
        System.out.println(t);
    }
     
    //一对一嵌套查询方式：根据教师id查询班级信息
    @Test
    public void testGetClasses2(){
        String statement = "one.to.one.classesMapper.getClasses2";
        Classes c = session.selectOne(statement, 1);
        System.out.println(c);
    }
     
     
 
}

4、MyBatis 入门实例 一对多，多对一 基于xml配置

这里我们以班级和学生为例，一个班级里面对应多个学生，这是一对多；反过来，多个学生对应一个班级，这是多对一

①、建立学生和班级的实体类

Student.java

package one.to.many;
 
public class Student {
    private int sid;
    private String sname;
    private Classes classes;
    public int getSid() {
        return sid;
    }
    public void setSid(int sid) {
        this.sid = sid;
    }
    public String getSname() {
        return sname;
    }
    public void setSname(String sname) {
        this.sname = sname;
    }
    public Classes getClasses() {
        return classes;
    }
    public void setClasses(Classes classes) {
        this.classes = classes;
    }
    @Override
    public String toString() {
        return "Student [sid=" + sid + ", sname=" + sname + ", classes=" + classes + "]";
    }
     
}

Classes.java

package one.to.many;
 
import java.util.Set;
 
public class Classes {
    private int cid;
    private String cname;
    private Set<Student> students;
     
    public int getCid() {
        return cid;
    }
    public void setCid(int cid) {
        this.cid = cid;
    }
    public String getCname() {
        return cname;
    }
    public void setCname(String cname) {
        this.cname = cname;
    }
    public Set<Student> getStudents() {
        return students;
    }
    public void setStudents(Set<Student> students) {
        this.students = students;
    }
    @Override
    public String toString() {
        return "Classes [cid=" + cid + ", cname=" + cname + ", students=" + students + "]";
    }
}

②、在数据库中根据实体类创建相应的数据表

③、多对一：定义操作 Classes 表的sql映射文件classesMapper.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="one.to.many.classesMapper">
    <select id="getClasses" resultMap="getClassesMap">
        select * from classes c,student s where s.cid=c.cid and c.cid=#{cid}
    </select>
    <resultMap type="one.to.many.Classes" id="getClassesMap">
        <id column="cid" property="cid"></id>
        <result column="cname" property="cname"/>
        <collection property="students" ofType="one.to.many.Student">
            <id column="sid" property="sid"/>
            <result column="sname" property="sname"/>
        </collection>
    </resultMap>
     
</mapper>

④、一对多：定义操作 Student 表的sql映射文件studentMapper.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="many.to.one.studentMapper">
    <select id="getStudents" resultMap="getStudentMap">
        select * from classes c,student s where s.cid=c.cid and s.sid=#{sid}
    </select>
    <resultMap type="one.to.many.Student" id="getStudentMap">
        <id column="sid" property="sid"></id>
        <result column="sname" property="sname"/>
        <association property="classes" javaType="one.to.many.Classes">
            <id column="cid" property="cid"/>
            <result column="cname" property="cname"/>
        </association>
    </resultMap>
     
</mapper>

⑤、向 mybatis-configuration.xml 配置文件中注册 classesMapper.xml 、studentMapper.xml文件

⑥、编写测试类

package one.to.many;
 
import java.io.InputStream;
 
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Before;
import org.junit.Test;
 
import com.ys.test.MyBatisTest;
 
public class OneToManyTest {
SqlSession session;
     
    @Before
    public void beforeLoadXML(){
        //加载 mybatis 配置文件
        InputStream inputStream = MyBatisTest.class.
                getClassLoader().getResourceAsStream("mybatis-configuration.xml");
        //构建sqlSession的工厂
        SqlSessionFactory sqlSessionFactory =
                new SqlSessionFactoryBuilder().build(inputStream);
        //根据 sqlSessionFactory 产生 session
        session = sqlSessionFactory.openSession();
    }
     
    //一对多嵌套结果方式：根据班级id查询班级所有的学生信息
    @Test
    public void testGetClasses(){
        String statement = "one.to.many.classesMapper.getClasses";
        Classes c = session.selectOne(statement, 1);
        System.out.println(c);
        System.out.println(c.getStudents().size());
    }
     
     
    //多对一嵌套结果方式：根据学生id查询班级信息
    @Test
    public void testGetStudents(){
        String statement = "many.to.one.studentMapper.getStudents";
        Student s = session.selectOne(statement, 1);
        System.out.println(s);
        System.out.println(s.getClasses());
    }
}

5、MyBatis 入门实例 多对多 基于xml配置

这里我们以 users 表和 groups 表为例，一个 users 可能加入多个 groups，而一个 groups 可能包含多个 users，故构成 多对多 的关联

①、在数据库中建立相应的表

users 表

groups 表

两者之间的关联表users_groups表

②、建立对应的实体类

Users.java

package many.to.many;
 
import java.util.Set;
 
public class Users {
    private int uid;
    private String uname;
    private Set<Groups> groups;
    public int getUid() {
        return uid;
    }
    public void setUid(int uid) {
        this.uid = uid;
    }
    public String getUname() {
        return uname;
    }
    public void setUname(String uname) {
        this.uname = uname;
    }
    public Set<Groups> getGroups() {
        return groups;
    }
    public void setGroups(Set<Groups> groups) {
        this.groups = groups;
    }
    @Override
    public String toString() {
        return "User [uid=" + uid + ", uname=" + uname + ", groups=" + groups + "]";
    }
     
}

Groups.java

package many.to.many;
 
import java.util.Set;
 
public class Groups {
    private int gid;
    private String gname;
    private Set<Users> users;
    public int getGid() {
        return gid;
    }
    public void setGid(int gid) {
        this.gid = gid;
    }
    public String getGname() {
        return gname;
    }
    public void setGname(String gname) {
        this.gname = gname;
    }
    public Set<Users> getUsers() {
        return users;
    }
    public void setUsers(Set<Users> users) {
        this.users = users;
    }
    @Override
    public String toString() {
        return "Group [gid=" + gid + ", gname=" + gname + ", users=" + users + "]";
    }
     
}

Users_Groups.java

package many.to.many;
 
public class Users_Groups {
    private Users user;
    private Groups group;
    public Users getUser() {
        return user;
    }
    public void setUser(Users user) {
        this.user = user;
    }
    public Groups getGroup() {
        return group;
    }
    public void setGroup(Groups group) {
        this.group = group;
    }
 
}

③、多对多：定义操作 sql映射文件userMapper.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="many.to.many.userMapper">
    <!-- 给一个用户 id，查看该用户下的所有用户组信息 -->
    <select id="getUsers" resultMap="getGroupMap">
        select g.gid,g.gname from users_groups ug,groups g
            where ug.group_id=g.gid and ug.user_id=#{uid}
    </select>
    <resultMap type="many.to.many.Groups" id="getGroupMap">
        <id column="gid" property="gid"/>
        <result column="gname" property="gname"/>
        <collection property="users" ofType="many.to.many.Users">
            <id column="uid" property="uid"/>
        <result column="uname" property="uname"/>
        </collection>
    </resultMap>
     
</mapper>

⑤、向 mybatis-configuration.xml 配置文件中注册 userMapper.xml文件

⑥、编写测试类

//多对多：根据根据用户 id 查询所有的用户组信息

    @Test
    public void testGetGroups(){
        String statement = "many.to.many.userMapper.getUsers";
        List<Groups> listGroup = session.selectList(statement,1);
        for(Groups g : listGroup){
            System.out.println(g.toString());
        }
    }