MyBatis日记（五）：一对一关系，一对多关系

一对一关系：

首先在数据库中新增地址表（t_address）用于存储人员的地址信息：

 CREATE TABLE `t_address` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `country` varchar(100) DEFAULT NULL,
   `city` varchar(100) DEFAULT NULL,
   `district` varchar(100) DEFAULT NULL,
   PRIMARY KEY (`id`)
 ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8

然后在人员信息表（t_person）中增加addressId字段：

ALTER TABLE t_person ADD addressId int(11);

在com.Aiden.domain中新增地址信息的实体类（Address.java）：

 package com.Aiden.domain;
 
 public class Address {
 
     private Integer id;
     private String country;
     private String city;
     private String district;
     public Address() {
         super();
     }
     public Address(String country, String city, String district) {
         super();
         this.country = country;
         this.city = city;
         this.district = district;
     }
     public Address(Integer id, String country, String city, String district) {
         super();
         this.id = id;
         this.country = country;
         this.city = city;
         this.district = district;
     }
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getCountry() {
         return country;
     }
     public void setCountry(String country) {
         this.country = country;
     }
     public String getCity() {
         return city;
     }
     public void setCity(String city) {
         this.city = city;
     }
     public String getDistrict() {
         return district;
     }
     public void setDistrict(String district) {
         this.district = district;
     }
     @Override
     public String toString() {
         return "Address [id=" + id + ", country=" + country + ", city=" + city + ", district=" + district + "]";
     }
 }

在com.Aiden.dao中新增地址信息的接口（addressMapper.java）：

package com.Aiden.dao;
public interface addressMapper {}

在com.Aiden.dao中新增地址信息的映射文件（addressMapper.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.Aiden.dao.addressMapper">
 </mapper>

在Person实体类中增加address属性并添加get、set方法：

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

在com.Aiden.service包中创建新的Junit测试类（MyBatisDemo02.Java），并添加测试方法：

 package com.Aiden.service;
 
 import static org.junit.Assert.*;
 
 import java.util.List;
 
 import org.apache.ibatis.session.SqlSession;
 import org.apache.log4j.Logger;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 
 import com.Aiden.dao.personMapper;
 import com.Aiden.domain.Person;
 import com.Aiden.util.SqlSessionFactoryUtil;
 /**
  * 一对一、一对多关系映射
  * @author 郭祥跃
  *
  */
 public class MybatisDemo02 {
     private static Logger logger=Logger.getLogger(MybatisDemo02.class);
     private static SqlSession sqlSession=null;
     private static personMapper personMapper=null;
 
     @Before
     public void setUp() throws Exception {
         sqlSession=SqlSessionFactoryUtil.openSession();
         System.out.println(sqlSession);
         personMapper=sqlSession.getMapper(personMapper.class);
     }
 
     @After
     public void tearDown() throws Exception {
         sqlSession.close();
     }
 
     @Test
     public void testFindPersonWithAddressById() {
         logger.info("一对多关系映射");
         List<Person> person=personMapper.findPersonWithAddressById(3);
         System.out.println(person);
     }
 
 }

在personMapper.java文件中添加新的接口（findPersonWithAddressById）：

 /**
  * 根据ID查询人员及地址信息
  * @param id
  * @return
  */
 public List<Person> findPersonWithAddressById(Integer id);

在personMapper.xml文件中添加select查询：

 <select id="findPersonWithAddressById" parameterType="Integer" resultMap="resultPersonWithAddress">
    select * from t_person tp,t_address ta where tp.addressId=ta.id and tp.id=#{id}
 </select>

添加resultMap返回结果：此处resultMap标签有几种不同的实现，记之如下：

第一种：

 <resultMap type="Person" id="resultPersonWithAddress">
     <id property="id" column="id"/>
     <result property="name" column="name"/>
     <result property="age" column="age"/>
 
     <result property="address.id" column="id"/>
     <result property="address.country" column="country"/>
     <result property="address.city" column="city"/>
     <result property="address.district" column="district"/>
 </resultMap>

查询结果：

第二种：

 <resultMap type="Person" id="resultPersonWithAddress">
     <id property="id" column="id"/>
     <result property="name" column="name"/>
     <result property="age" column="age"/>
 
     <association property="address" resultMap="resultAddress"/>
 </resultMap>
 <resultMap type="Address" id="resultAddress">
     <id property="id" column="id"/>
     <result property="country" column="country"/>
     <result property="city" column="city"/>
     <result property="district" column="district"/>
 </resultMap>

查询结果：

第三种：

 <resultMap type="Person" id="resultPersonWithAddress">
     <id property="id" column="id" />
     <result property="name" column="name" />
     <result property="age" column="age" />
 
     <association property="address" javaType="Address">
         <id property="id" column="id" />
         <result property="country" column="country" />
         <result property="city" column="city" />
         <result property="district" column="district" />
     </association>
 </resultMap>

查询结果：

第四种(最常用)：

这种方法借助于Address的查询方法进行实现：

首先在addressMapper.java接口文件中，添加查询的接口：

 package com.Aiden.dao;
 
 import com.Aiden.domain.Address;
 
 public interface addressMapper {
     /**
      * 根据ID查询地址消息
      * @param id
      * @return
      */
     public Address findById(Integer id);
 }

然后在addressMapper.xml中添加select标签：

 <?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.Aiden.dao.addressMapper">
 
     <select id="findAddressById" parameterType="Integer" resultType="Address">
         select * from t_address where id=#{id}
     </select>
 
 </mapper>

修改personMapper.xml中的resultMap为：

 <resultMap type="Person" id="resultPersonWithAddress">
         <id property="id" column="id" />
         <result property="name" column="name" />
         <result property="age" column="age" />
         <association property="address" column="addressId" select="com.Aiden.dao.addressMapper.findAddressById"/>
 </resultMap>

查询结果：

一对多关系：

简单的说一对多的关系可以用多个一对一关系实现。

首先在数据库中新增公司信息表（t_company）用于存储人员的地址信息：

 CREATE TABLE `t_company` (
   `Id` int(11) NOT NULL AUTO_INCREMENT,
   `companyName` varchar(100) DEFAULT NULL,
   PRIMARY KEY (`Id`)
 ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8

然后在人员信息表（t_person）中增加addressId字段：

ALTER TABLE t_person ADD companyId int(11);

在com.Aiden.domain中新增公司信息的实体类（Company.java）：

 package com.Aiden.domain;
 
 import java.util.List;
 
 public class Company {
     private Integer id;
     private String companyName;
     private List<Person> persons;
     public Company() {
         super();
     }
     public Company(String companyName) {
         super();
         this.companyName = companyName;
     }
     public Company(Integer id, String companyName) {
         super();
         this.id = id;
         this.companyName = companyName;
     }
     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getCompanyName() {
         return companyName;
     }
     public void setCompanyName(String companyName) {
         this.companyName = companyName;
     }
     public List<Person> getPersons() {
         return persons;
     }
     public void setPersons(List<Person> persons) {
         this.persons = persons;
     }
     @Override
     public String toString() {
         return "Company [id=" + id + ", companyName=" + companyName + "]";
     }
 }

在com.Aiden.dao中新增公司信息的接口（companyMapper.java）：

 package com.Aiden.dao;
 
 import com.Aiden.domain.Company;
 
 public interface companyMapper {
     /**
      * 根据ID查询公司详情
      * @param id
      * @return
      */
     public Company findCompanyById(Integer id);
 
 }

在com.Aiden.dao中新增公司信息的映射文件（companyMapper.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.Aiden.dao.companyMapper">
 
     <resultMap type="Company" id="resultCompany">
         <id property="id" column="id"/>
         <result property="companyName" column="companyName"/>
         <collection property="persons" column="id" select="com.Aiden.dao.personMapper.findPersonWithByCompanyId"/>
     </resultMap>
 
     <select id="findCompanyById" parameterType="Integer" resultMap="resultCompany">
         select * from t_company where id=#{id}
     </select>
 
 </mapper>

在person实体类中添加company属性及get、set方法：

 private Company company;
 
 public Company getCompany() {
     return company;
 }
 public void setCompany(Company company) {
     this.company = company;
 }

在personMapper.java中添加新的查询接口：

/**
 * 根据公司Id查询人员信息
 * @param id
 * @return
 */
public List<Person> findPersonWithByCompanyId(Integer companyId);

在personMapper.xml添加查询select及resultMap：

 <select id="findPersonWithByCompanyId" parameterType="Integer" resultMap="resultPersonWithCompany">
         select * from t_person where companyId=#{companyId}
 </select>
 
 <resultMap type="Person" id="resultPersonWithCompany">
         <id property="id" column="id" />
         <result property="name" column="name" />
         <result property="age" column="age" />
         <association property="address" column="addressId" select="com.Aiden.dao.addressMapper.findAddressById"/>
         <association property="company" column="companyId" select="com.Aiden.dao.companyMapper.findCompanyById"/>
 </resultMap>

在测试类MybatisDemo02.java中添加测试方法，运行：

 @Test
 public void testFindPersonWithByCompanyId() {
     logger.info("一对多关系映射——根据公司ID查询人员");
     List<Person> person=personMapper.findPersonWithByCompanyId(1);
     for (Person p : person) {
         System.out.println(p);
     }
 }

运行结果：