java web(六)：mybatis之一对一、一对多、多对多映射

前言：

　　百度百科：

　　　　MyBatis 是一款优秀的持久层框架，它支持定制化 SQL、存储过程以及高级映射。MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集。MyBatis 可　　　　以使用简单的 XML 或注解来配置和映射原生信息，将接口和 Java 的 POJOs(Plain Ordinary Java Object,普通的 Java对象)映射成数据库中的记录。

　　这篇文章讲解如何 使用mysql数据库，总结mybatis的一对一、一对多、多对多映射如何进行增删改查。

---

准备工作：

　　1.打开ecplise创建一个普通的java项目。项目结构如下图所示：

　　2.先看jar包，这次我们用到4个jar包，单元测试jar包junit-4.7.jar,日志包log4j-1.2.17.jar,mybatis所用的jar包以及连接mysql数据库用到的mysql-connector-java-5.1.47.jar

【ojdbc14.jar是连接oracle数据库用到的jar包】。

　　注：jar包记得build path

　　3.dtd约束文件：是对全局配置文件和sql映射文件的约束。在ecplise中点击 window --> preference ,在输入栏键入xml，然后选择 XML Catalog,点击Add。

　

　　注：-//mybatis.org//DTD Mapper 3.0//EN  、-//mybatis.org//DTD Config 3.0//EN ，key值是规定的，location是点击workspace在项目中选择的约束文件。

　　4.driver.properties配置文件是连接数据库所用到的配置信息。在mybaits-config.xml中会用到。

#基于mysql数据库
driver=com.mysql.jdbc.Driver
#?useUnicode=true&characterEncoding=utf8为了支持中文数据的写入
url=jdbc:mysql://188.131.246.182:3306/cnblogs?useUnicode=true&characterEncoding=utf-8
username=study
password=123456

#基于Oracle数据库
#driver=oracle.jdbc.driver.OracleDriver
#url=jdbc:oracle:thin:@127.0.0.1:1521:XE
#username=briup
#password=briup

　　5.log4j.properties是日志jar包要用到的配置文件。其中定义了输出日志级别、输出位置以及是否打印sql语句。

log4j.rootLogger=DEBUG, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d [%-5p] %c - %m%n
#show sql
log4j.logger.java.sql.ResultSet=INFO
log4j.logger.org.apache=INFO
log4j.logger.java.sql.Connection=DEBUG
log4j.logger.java.sql.Statement=DEBUG
log4j.logger.java.sql.PreparedStatement=DEBUG

　　6.全局配置文件：mybatis-config.xml。该文件的详细信息可网上找资料。我这里给一个简单能用的。

<?xml version="1.0" encoding="UTF-8"?>
<!-- dtd约束 -->
<!DOCTYPE  configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd" >
<configuration>
    <!-- properties必须是第一个子标签
         定义变量,定义完成后，可以在后面的标签中使用
         resource引入配置文件，优先级更高
    -->
    <properties resource="driver.properties">
        <property name="driver" value=""/>
        <property name="url" value=""/>
        <property name="username" value=""/>
        <property name="password" value=""/>
    </properties>

    <typeAliases>
　　　　　<!-- 给包下的类定义别名 -->
        <package name="com.cnblogs.bean"/>
    </typeAliases>

    <!-- 使用mysql数据库,如果要切换到Oracle数据库,default="oracle" -->
    <environments default="mysql">
        <!-- mysql -->
        <environment id="mysql">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}" />
                <property name="url" value="${url}" />
                <property name="username" value="${username}" />
                <property name="password" value="${password}" />
            </dataSource>
        </environment>

        <!-- oracle -->
        <environment id="oracle">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}" />
                <property name="url" value="${url}" />
                <property name="username" value="${username}" />
                <property name="password" value="${password}" />
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/cnblogs/OneToMany/OneToMany.xml" />
    </mappers>

</configuration>

　　

　　准备工作完成以后就可以开始写sql语句了。

---

　　　注：嵌套结果查询：一次查一张表，分多次查。

　　　　　 嵌套结果映射：一次查多张表，分别映射。　　　　　　　　　　　　　　　　　　

　　　　　　　　　　　　　　　　　　一对一映射

1.创建bean类：Student【学生】、FoodCard【饭卡】

　　Student.java

package com.cnblogs.bean;
/**
 *  和饭卡一一对应
 *  CREATE TABLE `student` (
      `id` int(11) NOT NULL AUTO_INCREMENT,
      `name` varchar(255) NOT NULL,
      `gender` varchar(255) NOT NULL,
      `age` int(11) DEFAULT NULL,
      PRIMARY KEY (`id`)
    )
 *
 */
public class Student {

    private Integer id;

    private String name;

    private String gender;

    private int age;

    public Student() {
        super();
        // TODO Auto-generated constructor stub
    }

    public Student(String name, String gender, int age) {
        super();
        this.name = name;
        this.gender = gender;
        this.age = age;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", gender=" + gender +
                ", age=" + age + "]";
    }

}

　　FoodCard.java

package com.cnblogs.bean;
/**
 * 饭卡，和学生一对一映射
 * CREATE TABLE `food_card` (
      `id` int(11) NOT NULL AUTO_INCREMENT,
      `number` varchar(255) NOT NULL,
      `balance` double DEFAULT NULL,
      `stu_id` int(11) NOT NULL,
      PRIMARY KEY (`id`),
      KEY `stu_id` (`stu_id`),
      CONSTRAINT `stu_id` FOREIGN KEY (`stu_id`) REFERENCES `student` (`id`)
    )
 *
 */
public class FoodCard {
    private Integer id;

    // 卡号
    private String number;

    //余额
    private Double balance;

    // 对应的学生
    private Student stu;

    public FoodCard() {
        super();
        // TODO Auto-generated constructor stub
    }

    public FoodCard(String number, Double balance) {
        super();
        this.number = number;
        this.balance = balance;
    }

    public FoodCard(String number, Double balance, Student stu) {
        super();
        this.number = number;
        this.balance = balance;
        this.stu = stu;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public Double getBalance() {
        return balance;
    }

    public void setBalance(Double balance) {
        this.balance = balance;
    }

    public Student getStu() {
        return stu;
    }

    public void setStu(Student stu) {
        this.stu = stu;
    }

    @Override
    public String toString() {
        return "FoodCard [id=" + id + ", number=" + number + ", balance=" +
                balance + ", stu=" + stu + "]";
    }

}

3.编写sql映射文件。首先告诉mybatis那个xml文件是你的映射文件。在mybatis的<Mappers>标签中添加一条

" <mapper resource="com/cnblogs/oneToOne/OneToOne.xml"/> " 按住Ctrl+鼠标左键点击跳转到xml映射文件代表配置成功。

<?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">
<!-- com.cnblogs.oneToOne.OneToOne是我们定义接口的全限定名字 这样就可以使用接口调用映射的SQL语句了 这个
        名字一定要和接口对应上-->
<mapper namespace="com.cnblogs.oneToOne.OneToOne">

    <!-- 插入一条学生信息 -->
    <insert id="insertStudent" parameterType="Student" useGeneratedKeys="true"
            keyProperty="id">
        insert into student(name,gender,age)
        values(#{name},#{gender},#{age})
    </insert>

    <!-- 插入一条饭卡信息 自动生成主键
          #{number}代表调用getNumber()方法
      -->
    <insert id="insertFoodCard" parameterType="FoodCard" useGeneratedKeys="true"
            keyProperty="id">
        insert into food_card(number,balance,stu_id)
        values(#{number},#{balance},#{stu.id})
    </insert>

    <!-- 删除一条饭卡信息-->
    <delete id="deleteFoodCardById" parameterType="int">
         delete from food_card where id=#{id}
    </delete>

    <!-- 根据学生id删除一条饭卡信息 -->
    <delete id="deleteFoodCardByStuId" parameterType="int">
        delete from food_card where stu_id=#{id}
    </delete>
    <!-- 删除一条学生信息 由于主键被饭卡表引用,需要级联删除,先调用deleteFoodCardByStuId   -->
    <delete id="deleteStudentById" parameterType="int">
        delete from student where id=#{id}
    </delete>

    <!-- 模拟一个业务需求：假设一批学生毕业了，需要删除关于这批学生的所有饭卡信息 -->
    <delete id="deleteFoodCardByStuIds" parameterType="java.util.List">
        delete from food_card where stu_id in(
            <foreach collection="list" item="stu" separator="," >
                #{stu.id}
            </foreach>
         )
    </delete>

    <!-- 如果方法要传入两个参数,#{param1}代表第一个参数,#{param2}代表第二个参数  -->
    <!-- 根据名字和年龄更改一条学生记录 -->
    <update id="updateStudentByNameAndAge">
        update student set age=21
        where name=#{param1} and age=#{param2}
    </update>

    <!-- 一对一映射
         查询两张表food_card和student,如何将student查到的记录映射到
         FoodCard对象中？
      -->
     <resultMap type="Student" id="StudentMap">
         <id column="id" property="id" />
         <result column="name" property="name"/>
         <result column="gender" property="gender"/>
         <result column="age" property="age"/>
     </resultMap>

     <!-- 嵌套结果映射 -->
     <resultMap type="FoodCard" id="FoodCardMap">
         <id column="id" property="id" />
         <result column="number" property="number"/>
         <result column="balance" property="balance"/>
         <!-- 一对一映射,将很多列映射到stu属性上 -->
         <association property="stu" resultMap="StudentMap" />
     </resultMap>

    <select id="selectFoodCardWithStudent" parameterType="int" resultMap="FoodCardMap">
        select * from student stu,food_card fc
        where fc.id=#{id} and fc.stu_id=stu.id
    </select>

    <!-- 嵌套结果查询 -->
    <select id="selectStudentById" resultType="Student">
        select * from student where id=#{id}
    </select>
    <resultMap type="FoodCard" id="FoodCardMap2">
         <id column="id" property="id" />
         <result column="number" property="number"/>
         <result column="balance" property="balance"/>
         <!-- 一对一  嵌套结果查询-->
         <association property="stu" select="selectStudentById" column="stu_id"/>
     </resultMap>
    <select id="selectFoodCardWithStudent2" parameterType="int" resultMap="FoodCardMap2">
        select * from food_card fc where fc.id=#{id}
    </select>

</mapper>

　　　　　　*嵌套结果映射：

　　<!-- 嵌套结果映射 -->

<resultMap type="FoodCard" id="FoodCardMap">

　　<id column="id" property="id" />

　　<result column="number" property="number"/>

　　<result column="balance" property="balance"/>

　　 <!-- 一对一映射,将很多列映射到stu属性上 -->

　　<association property="stu" resultMap="StudentMap" />

</resultMap>

<select id="selectFoodCardWithStudent" parameterType="int" resultMap="FoodCardMap">

　　select * from student stu,food_card fc where fc.id=#{id} and fc.stu_id=stu.id

</select>

　　

　　resultMap标签，type属性表示和那种类型对应，id值起唯一标识作用，主键用id标签，表的其它列用result标签，column代表和数据库表对应的列，property

表示type值对应的属性【property指getXXX和setXXX】，column和property组合起来表示把查到的记录对应的列映射到对应的属性上。

　　嵌套结果查询的SQL语句，返回值不能再用resultType指定了，用resultMap指定。

注：嵌套结果映射中,如果两个表有同名的列，自然链接的时候只会保留一个列，上述中如果直接 'select * ' 会导致饭卡id和学生id一致。

必须显式的指定返回的列, ' select fc.id,fc.number,fc.balance,fc.stu_id,stu.id,stu.name,stu.age,stu.gender

from student stu,food_card fc where fc.id=#{id} and fc.stu_id=stu.id'。嵌套结果查询不需要显式指定。

　　

　　　　*嵌套结果查询

<!-- 嵌套结果查询 -->
<select id="selectStudentById" resultType="Student">
        select * from student where id=#{id}
</select>
<resultMap type="FoodCard" id="FoodCardMap2">
      <id column="id" property="id" />
      <result column="number" property="number"/>
      <result column="balance" property="balance"/>
      <!-- 一对一  嵌套结果查询-->
       <association property="stu" select="selectStudentById" column="stu_id"/>
</resultMap>
<select id="selectFoodCardWithStudent2" parameterType="int" resultMap="FoodCardMap2">
     select * from food_card fc where fc.id=#{id}
</select>
　　
　　一次查一张表，多次查。<association property="stu" select="selectStudentById" column="stu_id"/>
property代表映射到那个属性,select代表调用那个方法，column指定当前查表返回的那个列作为方法的参数。如果
还需要再查一张表，按照规则再加一条<association>
　

　　　　所有的sql语句对应的接口中必须有该方法。　

package com.cnblogs.oneToOne;

import java.util.List;

import com.cnblogs.bean.FoodCard;
import com.cnblogs.bean.Student;

public interface OneToOne {
    /**
     * 插入一条饭卡信息
     */
    public abstract void insertFoodCard(FoodCard foodCard);

    /**
     * 插入一条学生信息
     */
    public abstract void insertStudent(Student stu);

    /**
     * 删除一条饭卡记录
     */
    public abstract void deleteFoodCardById(Integer id);

    /**
     * 根据学生id删除一条饭卡记录
     */
    public abstract void deleteFoodCardByStuId(Integer id);

    /**
     * 删除一条学生记录根据id
     * 调用该方(法应该先调用deleteFoodCardByStuId(Integer)
     */
    public abstract void deleteStudentById(Integer id);

    /**
     * 提供一批学生信息，删除对应的饭卡
     */
    public abstract void deleteFoodCardByStuIds(List<Student> stus);

    /**
     * 根据年龄和姓名更改一条学生记录
     */
    public abstract void updateStudentByNameAndAge(String name,Integer age);

    /**
     * 根据id查找饭卡的详细信息[包括学生属性]
     * 使用嵌套结果映射
     */
    public abstract FoodCard selectFoodCardWithStudent(Integer id);

    /**
     * 根据id查找学生记录
     */
    public abstract Student selectStudentById(Integer id);

    /**
     * 根据id查找饭卡的详细信息[包括学生属性]
     * 使用嵌套结果查询
     */
    public abstract FoodCard selectFoodCardWithStudent2(Integer id);
}

　　　　单元测试类：

package com.cnblogs.jtest;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;

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

import com.cnblogs.bean.FoodCard;
import com.cnblogs.bean.Student;
import com.cnblogs.oneToOne.OneToOne;
import com.cnblogs.utils.MySqlSessionFactory;

public class OneToOneTest {

    @Test
    public void insertStudent() {
        Student student1 = new Student("jack","男",20);
        Student student2 = new Student("Tina", "女", 16);

        InputStream inputStream;
        try{
            // 读取配置文件
            inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSessionFactory sqlSessionFactory = new
                    SqlSessionFactoryBuilder().build(inputStream);
            // 手动提交事务
            SqlSession sqlSession = sqlSessionFactory.openSession(false);

            OneToOne mapper = sqlSession.getMapper(OneToOne.class);
            mapper.insertStudent(student1);
            mapper.insertStudent(student2);

            // 提交事务
            sqlSession.commit();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    @Test
    public void insertFoodCard() {
        Student stu1 = new Student();
        stu1.setId(15);
        Student stu2 = new Student();
        stu2.setId(16);

        FoodCard foodCard1 = new FoodCard("123456",100.0,stu1);
        FoodCard foodCard2 = new FoodCard("123457",312.4,stu2);

        InputStream inputStream;
        try{
            // 读取配置文件
            inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSessionFactory sqlSessionFactory = new
                    SqlSessionFactoryBuilder().build(inputStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();

            OneToOne mapper = sqlSession.getMapper(OneToOne.class);
            mapper.insertFoodCard(foodCard1);
            mapper.insertFoodCard(foodCard2);

            // 提交事务
            sqlSession.commit();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    @Test
    public void deleteFoodCardById() {
        InputStream inputStream;
        try{
            // 读取配置文件
            inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSessionFactory sqlSessionFactory = new
                    SqlSessionFactoryBuilder().build(inputStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();

            OneToOne mapper = sqlSession.getMapper(OneToOne.class);
            mapper.deleteFoodCardById(5);

            // 提交事务
            sqlSession.commit();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    @Test
    public void deleteStudentById() {
        InputStream inputStream;
        try{
            // 读取配置文件
            inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSessionFactory sqlSessionFactory = new
                    SqlSessionFactoryBuilder().build(inputStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();

            OneToOne mapper = sqlSession.getMapper(OneToOne.class);
            mapper.deleteFoodCardByStuId(6);
            mapper.deleteStudentById(6);
            // 提交事务
            sqlSession.commit();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    @Test
    public void deleteFoodCardByStuIds() {
        InputStream inputStream;
        try{
            // 读取配置文件
            inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSessionFactory sqlSessionFactory = new
                    SqlSessionFactoryBuilder().build(inputStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();

            OneToOne mapper = sqlSession.getMapper(OneToOne.class);

            Student stu1 = new Student();
            stu1.setId(5);
            Student stu2 = new Student();
            stu2.setId(7);
            Student stu3 = new Student();
            stu3.setId(10);
            ArrayList<Student> stus = new ArrayList<Student>();
            stus.add(stu1);
            stus.add(stu2);
            stus.add(stu3);

            mapper.deleteFoodCardByStuIds(stus);

            // 提交事务
            sqlSession.commit();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    @SuppressWarnings("unused")
    @Test
    public void updateStudentByNameAndAge() {
        SqlSession sqlSession = null;
        try {
            // 手动提交事务
            sqlSession = MySqlSessionFactory.opensession();
            OneToOne mapper = sqlSession.getMapper(OneToOne.class);

            mapper.updateStudentByNameAndAge("jack", 20);

            sqlSession.commit();
        } catch (IOException e) {
            if(sqlSession != null)
                sqlSession.rollback();
            e.printStackTrace();
        }
    }

    @Test
    public void selectFoodCardWithStudent() {
        SqlSession sqlSession = null;
        try {
            sqlSession = MySqlSessionFactory.opensession();
            OneToOne mapper = sqlSession.getMapper(OneToOne.class);

            FoodCard foodCard = mapper.selectFoodCardWithStudent(12);
            System.out.println(foodCard);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void selectFoodCardWithStudent2() {
        SqlSession sqlSession = null;
        try {
            sqlSession = MySqlSessionFactory.opensession();
            OneToOne mapper = sqlSession.getMapper(OneToOne.class);

            FoodCard foodCard = mapper.selectFoodCardWithStudent2(12);
            System.out.println(foodCard);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

　　　　获得SqlSesion对象的步骤重多，我们可以进行封装成一个工厂类。

package com.cnblogs.utils;

import java.io.IOException;
import java.io.InputStream;

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 MySqlSessionFactory {
    
    public static SqlSessionFactory getSqlSessionFactory() throws IOException{
        // 读取配置文件
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        if(inputStream == null)
            throw new IOException("配置文件路径不对或者配置文件内容出错");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        return sqlSessionFactory;

    }
    
    /**
     * 
     * @param flag true 自动提交事务,false 手动提交事务
     * @return
     */
    public static SqlSession opensession(boolean flag) throws IOException{
        return getSqlSessionFactory().openSession(flag);
    }
    
    /**
     * 默认手动提交事务
     * @return
     */
    public static SqlSession opensession() throws IOException{
        return opensession(false);
    }
    
}

---

　　　　　　　　　　一对多映射

简单模拟一下映射关系,一个人只能有一个户籍所在地，而一个户籍所在地可以对应许多人。把外键放在一的那边。

1)pojo类：

Human.java

package com.cnblogs.bean;

import java.util.Date;

/**
 * create table human(
 *     id int,
 *  name varchar,
 *  gender varchar,
 *  age int,
 *  dob datetime,
 *  address_id int reference address(id)
 * )
 *
 */
public class Human {
    private Integer id;

    private String name;

    private String gender;

    private Integer age;

    private Date dob;
    // 人对应的地址
    private Address address;

    public Human() {
        super();
    }

    public Human(String name, String gender, Integer age, Date dob) {
        super();
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.dob = dob;
    }

    public Human(String name, String gender, Integer age, Date dob, Address address) {
        super();
        this.name = name;
        this.gender = gender;
        this.age = age;
        this.dob = dob;
        this.address = address;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Date getDob() {
        return dob;
    }

    public void setDob(Date dob) {
        this.dob = dob;
    }

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Human [id=" + id + ", name=" + name + ", gender=" + gender + ", age=" + age +
                ", dob=" + dob + ", address=" + address + "]";
    }

}

Address.java

package com.cnblogs.bean;

import java.util.List;

/**
 * table
 * address(
 *     id int key,
 *     province varchar,
 *  city varchar,
 *  street varchar
 * )
 *
 */
public class Address {
    private Integer id;

    private String province;

    private String city;

    private String street;
    // 地址对应的人
    private List<Human> humans;

    public Address() {
        super();
    }

    public Address(String province, String city, String street) {
        super();
        this.province = province;
        this.city = city;
        this.street = street;
    }

    public Address(String province, String city, String street, List<Human> humans) {
        super();
        this.province = province;
        this.city = city;
        this.street = street;
        this.humans = humans;
    }

    public Address(Integer id, String province, String city, String street) {
        super();
        this.id = id;
        this.province = province;
        this.city = city;
        this.street = street;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getProvince() {
        return province;
    }

    public void setProvince(String province) {
        this.province = province;
    }

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getStreet() {
        return street;
    }

    public void setStreet(String street) {
        this.street = street;
    }

    public List<Human> getHumans() {
        return humans;
    }

    public void setHumans(List<Human> humans) {
        this.humans = humans;
    }

    @Override
    public String toString() {
        return "Address [id=" + id + ", province=" + province + ", city=" + city +
                ", street=" + street + "]";
    }

}

2)在mybatis<Mappers>下加一条：<mapper resource="com/cnblogs/oneToMany/OneToMany.xml" />

3)编写OneToMany.xml和OneTomany.java接口

<?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">
<!-- com.cnblogs.OneToMany.OneToMany是我们定义接口的全限定名字 这样就可以使用接口调用映射的SQL语句了 这个
        名字一定要和接口对应上-->
<mapper namespace="com.cnblogs.oneToMany.OneToMany">
    <!-- 插入一条地址信息 -->
    <insert id="insertAddress" parameterType="Address"
            useGeneratedKeys="true" keyProperty="id">
        insert into address(province,city,street)
        values(#{province},#{city},#{street})
    </insert>

    <!-- 插入一条人类信息 -->
    <insert id="insertHuman" parameterType="Human"
            useGeneratedKeys="true" keyProperty="id">
        insert into human(name,gender,age,dob,address_id)
        values(#{name},#{gender},#{age},#{dob},#{address.id})
    </insert>

    <!-- 删改类似，省略.... -->

    <!-- 结果集映射
         基础结果集,说明了如何从数据库加载对象
     -->
    <resultMap type="Address" id="addressBaseMap">
        <id property="id" column="id" />
        <result property="province" column="province"/>
        <result property="city" column="city"/>
        <result property="street" column="street"/>
    </resultMap>
    <resultMap type="Human" id="humanBaseMap">
        <id property="id" column="id" />
        <result property="name" column="name"/>
        <result property="gender" column="gender"/>
        <result property="age" column="age"/>
        <result property="dob" column="dob"/>
    </resultMap>

    <!-- 结果集映射
         一个人对应一个户籍,所以这里还是一对一映射
         继承基础结果集
      -->
    <!-- 嵌套结果映射
         继承：namespace + id 完全限定名
     -->
    <resultMap type="Human" id="humanMap"
                extends="com.cnblogs.oneToMany.OneToMany.humanBaseMap">
        <!-- 避免human的id和address的id起冲突,sql语句会给列起别名，相应的这里也需要更改 -->
        <id property="id" column="hid" />
        <association property="address" resultMap="addressBaseMap"></association>
    </resultMap>
    <select id="selectHumanWithAddressById" parameterType="int" resultMap="humanMap">
        select h.id hid,h.name,h.gender,h.age,h.dob,a.*
        from human h,address a
        where h.id=#{id} and h.address_id = a.id
    </select>

    <!-- 一对多
         一个户籍地对应多个人
     -->
     <!-- 嵌套结果映射 -->
     <resultMap type="Address" id="AddressMap"
                 extends="com.cnblogs.oneToMany.OneToMany.addressBaseMap">
         <!-- 避免human的id和address的id起冲突,sql语句会给列起别名，相应的这里也需要更改  -->
         <id property="id" column="aid"/>
         <!-- 一对多使用collection集合 -->
         <collection property="humans" resultMap="humanBaseMap" />
     </resultMap>
     <!-- 嵌套结果映射sql语句 -->
     <select id="selectAddressWithHumanById" parameterType="int" resultMap="AddressMap">
         select a.id aid,a.province,a.city,a.street,h.*
         from address a,human h
         where a.id=#{id} and a.id=h.address_id
     </select>

     <!-- 嵌套结果查询 -->
     <!-- 嵌套结果查询中被用到的另一条sql语句 -->
     <select id="selectHumanByAddressId" parameterType="int" resultMap="humanBaseMap">
         select * from human
         where address_id=#{id}
     </select>
     <!-- 结果集 -->
     <resultMap type="Address" id="AddressMap2"
                 extends="com.cnblogs.oneToMany.OneToMany.addressBaseMap">
         <!-- 把id传过去 -->
         <collection property="humans" select="selectHumanByAddressId" column="id" />
     </resultMap>
     <!-- 嵌套结果查询sql语句  -->
     <select id="selectAddressWithHumanById2" parameterType="int" resultMap="AddressMap2">
         select * from address
         where id=#{id}
     </select>

</mapper>

OneTOMany.java

package com.cnblogs.oneToMany;

import java.util.List;

import com.cnblogs.bean.Address;
import com.cnblogs.bean.Human;

public interface OneToMany {
    /**
     * 插入一条地址信息
     * @param address
     */
    public abstract void insertAddress(Address address);

    /**
     * 插入一条人类信息
     * @param humam
     */
    public abstract void insertHuman(Human humam);

    /**
     * 根据id查询一条人类信息[包括户籍的详细信息]
     * @param id
     */
    public abstract Human selectHumanWithAddressById(Integer id);

    /**
     * 嵌套结果映射
     * 根据id查询一条户籍信息[包括户籍所在地人的信息]
     * @param id
     * @return
     */
    public abstract Address selectAddressWithHumanById(Integer id);

    /**
     * 根据户籍地id查找人
     * @param id
     * @return
     */
    public abstract List<Human> selectHumanByAddressId(Integer id);

    /**
     * 嵌套结果查询
     * 根据id查询一条户籍信息[包括户籍所在地人的信息]
     * @param id
     * @return
     */
    public abstract Address selectAddressWithHumanById2(Integer id);
}

4)测试类

package com.cnblogs.jtest;

import java.io.IOException;
import java.util.Date;
import java.util.List;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import com.cnblogs.bean.Address;
import com.cnblogs.bean.Human;
import com.cnblogs.oneToMany.OneToMany;
import com.cnblogs.utils.MySqlSessionFactory;

public class OnetoManyTest {

    @Test
    public void insertHumanAndAddress() {
        try{
            SqlSession sqlSession = MySqlSessionFactory.opensession();
            OneToMany mapper = sqlSession.getMapper(OneToMany.class);

            // 准备数据
            Address address1 = new Address("湖南", "张家界", "步行街");
            Address address2 = new Address("湖南", "长沙", "步行街");

            mapper.insertAddress(address1);
            mapper.insertAddress(address2);

            //提交事务
            sqlSession.commit();

        } catch(Exception e) {
            e.printStackTrace();
        }

    }

    @SuppressWarnings("unused")
    @Test
    public void insertHuman() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            OneToMany mapper = session.getMapper(OneToMany.class);
            // 准备数据
            Address address1 = new Address();
            address1.setId(3);
            Address address2 = new Address();
            address2.setId(4);
            Human human1 = new Human("jack","男",22,new Date(),address1);
            Human human2 = new Human("tom","男",20,new Date(),address2);
            Human human3 = new Human("tina","女",22,new Date(),address1);
            Human human4 = new Human("alias","女",18,new Date(),address1);
            // 插入数据
            mapper.insertHuman(human1);
            mapper.insertHuman(human2);
            mapper.insertHuman(human3);
            mapper.insertHuman(human4);
            // 提交事务
            session.commit();
        } catch (IOException e) {
            if(session != null)
                session.close();
            e.printStackTrace();
        }
    }

    @SuppressWarnings("unused")
    @Test
    public void selectHumanWithAddressById() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            OneToMany mapper = session.getMapper(OneToMany.class);

            Human human1 = mapper.selectHumanWithAddressById(1);
            Human human2 = mapper.selectHumanWithAddressById(3);
            System.out.println("human: " + human1);
            System.out.println("human: " + human2);
        } catch (IOException e) {
            if(session != null)
                session.close();
            e.printStackTrace();
        }
    }

    @SuppressWarnings("unused")
    @Test
    public void selectAddressWithHumanById() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            OneToMany mapper = session.getMapper(OneToMany.class);

            Address address1 = mapper.selectAddressWithHumanById(3);
            Address address2 = mapper.selectAddressWithHumanById(4);

            System.out.println("address: " + address1);
            List<Human> humans1 = address1.getHumans();
            System.out.println("humans : ");
            for(Human h : humans1)
                System.out.println(h);
            System.out.println("============================");
            System.out.println("address: " + address2);
            List<Human> humans2 = address2.getHumans();
            System.out.println("humans : ");
            for(Human h : humans2)
                System.out.println(h);
        } catch (IOException e) {
            if(session != null)
                session.close();
            e.printStackTrace();
        }
    }

    @SuppressWarnings("unused")
    @Test
    public void selectAddressWithHumanById2() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            OneToMany mapper = session.getMapper(OneToMany.class);

            Address address1 = mapper.selectAddressWithHumanById2(3);
            Address address2 = mapper.selectAddressWithHumanById2(4);

            System.out.println("address: " + address1);
            List<Human> humans1 = address1.getHumans();
            System.out.println("humans : ");
            for(Human h : humans1)
                System.out.println(h);
            System.out.println("============================");
            System.out.println("address: " + address2);
            List<Human> humans2 = address2.getHumans();
            System.out.println("humans : ");
            for(Human h : humans2)
                System.out.println(h);
        } catch (IOException e) {
            if(session != null)
                session.close();
            e.printStackTrace();
        }
    }
}

---

　　　　　　　　　　　　　　　　多对多　

描述：一个老师可以讲多门课，一门课可以有多个老师教。

1）pojo类

Teacher.java

package com.cnblogs.bean;

import java.util.List;
/**
 * 教师类
 * 和课程对多多
 */
public class Teacher {
    // 教师id
    private Long id;
    // 教师名称
    private String name;
    // 教师职称 讲师 高级讲师 教授
    private String title;
    // 教师讲授的课程
    private List<Course> courses;

    public Teacher() {
        super();
    }

    public Teacher(String name, String title) {
        super();
        this.name = name;
        this.title = title;
    }

    public Teacher(String name, String title, List<Course> courses) {
        super();
        this.name = name;
        this.title = title;
        this.courses = courses;
    }

    public Teacher(Long id, String name, String title, List<Course> courses) {
        super();
        this.id = id;
        this.name = name;
        this.title = title;
        this.courses = courses;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public List<Course> getCourses() {
        return courses;
    }

    public void setCourses(List<Course> courses) {
        this.courses = courses;
    }

    @Override
    public String toString() {
        return "Teacher [id=" + id + ", name=" + name + ", title=" + title + ", courses=" + courses + "]";
    }

}

Course.java

package com.cnblogs.bean;

import java.util.List;
/**
 * 课程类
 * 和教师多对多
 *
 */
public class Course {
    // 课程id
    private Long id;
    // 课程名称
    private String name;
    // 课程描述
    private String description;
    // 课程对应的老师
    private List<Teacher> teachers;

    public Course() {
        super();
    }

    public Course(String name, String description) {
        super();
        this.name = name;
        this.description = description;
    }

    public Course(String name, String description, List<Teacher> teachers) {
        super();
        this.name = name;
        this.description = description;
        this.teachers = teachers;
    }

    public Course(Long id, String name, String description, List<Teacher> teachers) {
        super();
        this.id = id;
        this.name = name;
        this.description = description;
        this.teachers = teachers;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public List<Teacher> getTeachers() {
        return teachers;
    }

    public void setTeachers(List<Teacher> teachers) {
        this.teachers = teachers;
    }

    @Override
    public String toString() {
        return "Course [id=" + id + ", name=" + name + ", description=" + description + "]";
    }

}

桥表类:TeacherCourse.java

package com.cnblogs.bean;

import java.util.Date;

/**
 * 桥表类
 * 连接教师类和课程类
 *
 */
public class TeacherCourse {
    // id
    private Long id;
    // 授课开始时间
    private Date begin;
    // 授课结束时间
    private Date end;
    // 教师
    private Teacher teacher;
    // 课程
    private Course course;

    public TeacherCourse() {
        super();
        // TODO Auto-generated constructor stub
    }

    public TeacherCourse(Date begin, Date end) {
        super();
        this.begin = begin;
        this.end = end;
    }

    public TeacherCourse(Date begin, Date end, Teacher teacher, Course course) {
        super();
        this.begin = begin;
        this.end = end;
        this.teacher = teacher;
        this.course = course;
    }

    public TeacherCourse(Long id, Date begin, Date end, Teacher teacher, Course course) {
        super();
        this.id = id;
        this.begin = begin;
        this.end = end;
        this.teacher = teacher;
        this.course = course;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Date getBegin() {
        return begin;
    }

    public void setBegin(Date begin) {
        this.begin = begin;
    }

    public Date getEnd() {
        return end;
    }

    public void setEnd(Date end) {
        this.end = end;
    }

    public Teacher getTeacher() {
        return teacher;
    }

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

    public Course getCourse() {
        return course;
    }

    public void setCourse(Course course) {
        this.course = course;
    }

    @Override
    public String toString() {
        return "TeacherCourse [id=" + id + ", begin=" + begin + ", end=" + end + ", teacher=" + teacher + ", course="
                + course + "]";
    }

}

2)在mybatis-config.xml的<Mappers>下加一条：<mapper resource="com/cnblogs/oneToMany/OneToMany.xml" />　　

3)sql映射文件

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.cnblogs.manyTOMany.ManyToMany">
    <!-- 结果集映射关系 -->
    <resultMap type="Teacher" id="TeacherBaseMap">
        <id property="id" column="t_id"/>
        <result property="name" column="t_name"/>
        <result property="title" column="t_title"/>
    </resultMap>

    <resultMap type="Course" id="CourseBaseMap">
        <id property="id" column="c_id"/>
        <result property="name" column="c_name"/>
        <result property="description" column="c_des"/>
    </resultMap>

    <resultMap type="TeacherCourse" id="TeacherCourseBaseMap">
        <id property="id" column="id"/>
        <result property="begin" column="begin"/>
        <result property="end" column="end"/>
    </resultMap>

    <!-- 插入 -->
    <insert id="insertTeacher" parameterType="Teacher"
            useGeneratedKeys="true" keyProperty="id">
        insert into teacher(t_name,t_title)
        values(#{name},#{title})
    </insert>

    <insert id="insertCourse" parameterType="Course"
            useGeneratedKeys="true" keyProperty="id">
        insert into course(c_name,c_des)
        values(#{name},#{description})
    </insert>

    <insert id="insertTeacherCourse" parameterType="TeacherCourse"
            useGeneratedKeys="true" keyProperty="id">
        insert into teacher_course(begin,end,t_id,c_id)
        values(#{begin},#{end},#{teacher.id},#{course.id})
    </insert>

    <!-- 嵌套结果映射
         其实就是一对多查询，因为桥表的存在
      -->
    <resultMap type="Teacher" id="TeacherMap1"
               extends="com.cnblogs.manyTOMany.ManyToMany.TeacherBaseMap">
        <collection property="courses" resultMap="CourseBaseMap" column="c_id" />
    </resultMap>
    <!-- sql语句 -->
    <select id="selectTeacherWithCourseById" parameterType="long" resultMap="TeacherMap1">
        select * from teacher t,course c,teacher_course tc
        where t.t_id=#{id} and t.t_id=tc.t_id and tc.c_id=c.c_id
    </select>

    <!-- 嵌套结果查询 -->
    <select id="selectCourseById" parameterType="long" resultMap="CourseBaseMap">
        select * from course
        where c_id=#{id}
    </select>
    <resultMap type="Teacher" id="TeacherMap2"
               extends="com.cnblogs.manyTOMany.ManyToMany.TeacherBaseMap">
        <collection property="courses" select="selectCourseById" column="c_id" />
    </resultMap>
    <select id="selectTeacherWithCourseById2" parameterType="long"
            resultMap="TeacherMap2">
        select * from teacher t,teacher_course tc
        where t.t_id=#{id} and t.t_id=tc.t_id
    </select>
</mapper>

　接口：

package com.cnblogs.manyTOMany;

import com.cnblogs.bean.Course;
import com.cnblogs.bean.Teacher;
import com.cnblogs.bean.TeacherCourse;

public interface ManyToMany {
    /**
     * 插入一条教师数据
     * @param teacher
     */
    public abstract void insertTeacher(Teacher teacher);

    /**
     * 插入一条课程数据
     * @param course
     */
    public abstract void insertCourse(Course course);

    /**
     * 插入一条桥表数据
     * @param tc
     */
    public abstract void insertTeacherCourse(TeacherCourse tc);

    /**
     * 嵌套结果映射
     * 教师的详细信息
     * @param id
     * @return
     */
    public abstract Teacher selectTeacherWithCourseById(Long id);

    /**
     * 嵌套结果查询
     * @param id
     * @return
     */
    public abstract Teacher selectTeacherWithCourseById2(Long id);
}

4）测试类

package com.cnblogs.jtest;

import java.io.IOException;
import java.util.Date;

import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import com.cnblogs.bean.Course;
import com.cnblogs.bean.Teacher;
import com.cnblogs.bean.TeacherCourse;
import com.cnblogs.manyTOMany.ManyToMany;
import com.cnblogs.utils.MySqlSessionFactory;

public class ManyToManyTest {
    @Test
    public void insertTeacher() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            ManyToMany mapper = session.getMapper(ManyToMany.class);
            // 准备数据
            Teacher teacher1 = new Teacher("li","讲师");
            Teacher teacher2 = new Teacher("zj","高级讲师");
            Teacher teacher3 = new Teacher("kb","教授");

            mapper.insertTeacher(teacher1);
            mapper.insertTeacher(teacher2);
            mapper.insertTeacher(teacher3);

            // 提交事务
            session.commit();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void insertCourse() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            ManyToMany mapper = session.getMapper(ManyToMany.class);
            // 准备数据
            Course course1 = new Course("core java","核心java基础");
            Course course2 = new Course("c语言","ccc");
            Course course3 = new Course("c++","c++++");

            mapper.insertCourse(course1);
            mapper.insertCourse(course2);
            mapper.insertCourse(course3);

            // 提交事务
            session.commit();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void insertTeacherCourse() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            ManyToMany mapper = session.getMapper(ManyToMany.class);
            // 准备数据
            Course course1 = new Course();
            course1.setId(1L);
            Course course2 = new Course();
            course2.setId(2L);
            Course course3 = new Course();
            course3.setId(3L);

            Teacher teacher1 = new Teacher();
            teacher1.setId(4L);
            Teacher teacher2 = new Teacher();
            teacher2.setId(5L);
            Teacher teacher3 = new Teacher();
            teacher3.setId(6L);

            TeacherCourse tc1 = new TeacherCourse(new Date(),new Date(),teacher1,course1);
            TeacherCourse tc2 = new TeacherCourse(new Date(),new Date(),teacher2,course2);
            TeacherCourse tc3 = new TeacherCourse(new Date(),new Date(),teacher3,course3);

            mapper.insertTeacherCourse(tc1);
            mapper.insertTeacherCourse(tc2);
            mapper.insertTeacherCourse(tc3);

            // 提交事务
            session.commit();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void selectTeacherWithCourseById() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            ManyToMany mapper = session.getMapper(ManyToMany.class);
            // 准备数据
            Teacher t1 = mapper.selectTeacherWithCourseById(4L);
            Teacher t2 = mapper.selectTeacherWithCourseById(6L);

            System.out.println("Teacher: " + t1);
            System.out.println("Teacher: " + t2);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Test
    public void selectTeacherWithCourseById2() {
        SqlSession session = null;
        try {
            session = MySqlSessionFactory.opensession();
            ManyToMany mapper = session.getMapper(ManyToMany.class);
            // 准备数据
            Teacher t1 = mapper.selectTeacherWithCourseById2(4L);
            Teacher t2 = mapper.selectTeacherWithCourseById2(6L);

            System.out.println("Teacher: " + t1);
            System.out.println("Teacher: " + t2);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

---

总结：

　　使用mybatis操作数据库，把配置文件配置好以后，就非常简单了，就像在sql命令行直接输入sql语句一样。

　要分清嵌套结果映射和嵌套结果查询的区别。

　　* resultMap – 是最复杂也是最强大的元素，用来描述如何从数据库结果集中来加载对象。

　　* 一对一：重点掌握<association>标签在嵌套结果映射和嵌套结果查询中的使用

　　* 一对多：重点掌握<collection>标签在嵌套结果映射和嵌套结果查询中的使用

　　* 多对多：其实和一对多一样使用，不过多了一个桥接表。

mybatis还有更强大的功能：动态sql，将会在下篇使用。同时还会介绍mybatis  generator软件【一款根据数据库的表自动生成pojo类和sql映射文件】

　　如何想了解更多mybatis，可以去看文档。中文文档网址：http://www.mybatis.org/mybatis-3。