MyBatis日记（五）：一对一关系，一对多关系

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：

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

然后在人员信息表（t_person）中增加addressId字段：

 1 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）：

 1 package com.Aiden.domain;
 2 
 3 public class Address {
 4     
 5     private Integer id;
 6     private String country;
 7     private String city;
 8     private String district;
 9     public Address() {
10         super();
11     }
12     public Address(String country, String city, String district) {
13         super();
14         this.country = country;
15         this.city = city;
16         this.district = district;
17     }
18     public Address(Integer id, String country, String city, String district) {
19         super();
20         this.id = id;
21         this.country = country;
22         this.city = city;
23         this.district = district;
24     }
25     public Integer getId() {
26         return id;
27     }
28     public void setId(Integer id) {
29         this.id = id;
30     }
31     public String getCountry() {
32         return country;
33     }
34     public void setCountry(String country) {
35         this.country = country;
36     }
37     public String getCity() {
38         return city;
39     }
40     public void setCity(String city) {
41         this.city = city;
42     }
43     public String getDistrict() {
44         return district;
45     }
46     public void setDistrict(String district) {
47         this.district = district;
48     }
49     @Override
50     public String toString() {
51         return "Address [>;
52     }
53 }

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）：

1 <?xml version="1.0" encoding="UTF-8"?>
2 <!DOCTYPE mapper
3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
4 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
5 <mapper namespace="com.Aiden.dao.addressMapper">
6 </mapper>

在Person实体类中增加address属性并添加get、set方法：

1 private Address address;
2 
3 public Address getAddress() {
4     return address;
5 }
6 public void setAddress(Address address) {
7     this.address = address;
8 }

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

 1 package com.Aiden.service;
 2 
 3 import static org.junit.Assert.*;
 4 
 5 import java.util.List;
 6 
 7 import org.apache.ibatis.session.SqlSession;
 8 import org.apache.log4j.Logger;
 9 import org.junit.After;
10 import org.junit.Before;
11 import org.junit.Test;
12 
13 import com.Aiden.dao.personMapper;
14 import com.Aiden.domain.Person;
15 import com.Aiden.util.SqlSessionFactoryUtil;
16 /**
17  * 一对一、一对多关系映射
18  * @author 郭祥跃
19  *
20  */
21 public class MybatisDemo02 {
22     private static Logger logger=Logger.getLogger(MybatisDemo02.class);
23     private static SqlSession sqlSession=null;
24     private static personMapper personMapper=null;
25 
26     @Before
27     public void setUp() throws Exception {
28         sqlSession=SqlSessionFactoryUtil.openSession();
29         System.out.println(sqlSession);
30         personMapper=sqlSession.getMapper(personMapper.class);
31     }
32 
33     @After
34     public void tearDown() throws Exception {
35         sqlSession.close();
36     }
37 
38     @Test
39     public void testFindPersonWithAddressById() {
40         logger.info("一对多关系映射");
41         List<Person> person=personMapper.findPersonWithAddressById(3);
42         System.out.println(person);
43     }
44 
45 }

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

1 /**
2  * 根据ID查询人员及地址信息
3  * @param id
4  * @return
5  */
6 public List<Person> findPersonWithAddressById(Integer id);

在personMapper.xml文件中添加select查询：

1 <select id="findPersonWithAddressById" parameterType="Integer" resultMap="resultPersonWithAddress">
2    select * from t_person tp,t_address ta where tp.addressId=ta.id and tp.id=#{id}
3 </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：

 1 <resultMap type="Person" id="resultPersonWithAddress">
 2     <id property="id" column="id"/>
 3     <result property="name" column="name"/>
 4     <result property="age" column="age"/>
 5         
 6     <result property="address.id" column="id"/>
 7     <result property="address.country" column="country"/>
 8     <result property="address.city" column="city"/>
 9     <result property="address.district" column="district"/>
10 </resultMap>

查询结果：

MyBatis日记（五）：一对一关系，一对多关系

 

第二种：

 1 <resultMap type="Person" id="resultPersonWithAddress">
 2     <id property="id" column="id"/>
 3     <result property="name" column="name"/>
 4     <result property="age" column="age"/>
 5         
 6     <association property="address" resultMap="resultAddress"/>
 7 </resultMap>
 8 <resultMap type="Address" id="resultAddress">
 9     <id property="id" column="id"/>
10     <result property="country" column="country"/>
11     <result property="city" column="city"/>
12     <result property="district" column="district"/>
13 </resultMap>

查询结果：

MyBatis日记（五）：一对一关系，一对多关系

 

第三种：

 1 <resultMap type="Person" id="resultPersonWithAddress">
 2     <id property="id" column="id" />
 3     <result property="name" column="name" />
 4     <result property="age" column="age" />
 5 
 6     <association property="address" javaType="Address">
 7         <id property="id" column="id" />
 8         <result property="country" column="country" />
 9         <result property="city" column="city" />
10         <result property="district" column="district" />
11     </association>
12 </resultMap>

查询结果：

MyBatis日记（五）：一对一关系，一对多关系

 

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：

 1 package com.Aiden.dao;
 2 
 3 import com.Aiden.domain.Address;
 4 
 5 public interface addressMapper {
 6     /**
 7      * 根据ID查询地址消息
 8      * @param id
 9      * @return
10      */
11     public Address findById(Integer id);
12 }

然后在addressMapper.xml中添加select标签：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 <mapper namespace="com.Aiden.dao.addressMapper">
 6 
 7     <select id="findAddressById" parameterType="Integer" resultType="Address">
 8         select * from t_address where id=#{id}
 9     </select>
10     
11 </mapper>

修改personMapper.xml中的resultMap为：

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

查询结果：

MyBatis日记（五）：一对一关系，一对多关系

 

 

 

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：

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

然后在人员信息表（t_person）中增加addressId字段：

 1 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）：

 1 package com.Aiden.domain;
 2 
 3 import java.util.List;
 4 
 5 public class Company {
 6     private Integer id;
 7     private String companyName;
 8     private List<Person> persons;
 9     public Company() {
10         super();
11     }
12     public Company(String companyName) {
13         super();
14         this.companyName = companyName;
15     }
16     public Company(Integer id, String companyName) {
17         super();
18         this.id = id;
19         this.companyName = companyName;
20     }
21     public Integer getId() {
22         return id;
23     }
24     public void setId(Integer id) {
25         this.id = id;
26     }
27     public String getCompanyName() {
28         return companyName;
29     }
30     public void setCompanyName(String companyName) {
31         this.companyName = companyName;
32     }
33     public List<Person> getPersons() {
34         return persons;
35     }
36     public void setPersons(List<Person> persons) {
37         this.persons = persons;
38     }
39     @Override
40     public String toString() {
41         return "Company [>;
42     }
43 }

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

 1 package com.Aiden.dao;
 2 
 3 import com.Aiden.domain.Company;
 4 
 5 public interface companyMapper {
 6     /**
 7      * 根据ID查询公司详情
 8      * @param id
 9      * @return
10      */
11     public Company findCompanyById(Integer id);
12 
13 }

在com.Aiden.dao中新增公司信息的映射文件（companyMapper.xml）：

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <!DOCTYPE mapper
 3 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 4 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 5 <mapper namespace="com.Aiden.dao.companyMapper">
 6 
 7     <resultMap type="Company" id="resultCompany">
 8         <id property="id" column="id"/>
 9         <result property="companyName" column="companyName"/>
10         <collection property="persons" column="id" select="com.Aiden.dao.personMapper.findPersonWithByCompanyId"/>
11     </resultMap>
12 
13     <select id="findCompanyById" parameterType="Integer" resultMap="resultCompany">
14         select * from t_company where id=#{id}
15     </select>
16 
17 </mapper>

在person实体类中添加company属性及get、set方法：

1 private Company company;
2 
3 public Company getCompany() {
4     return company;
5 }
6 public void setCompany(Company company) {
7     this.company = company;
8 }

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：

 1 <select id="findPersonWithByCompanyId" parameterType="Integer" resultMap="resultPersonWithCompany">
 2         select * from t_person where companyId=#{companyId}
 3 </select>
 4 
 5 
 6 <resultMap type="Person" id="resultPersonWithCompany">
 7         <id property="id" column="id" />
 8         <result property="name" column="name" />
 9         <result property="age" column="age" />
10         <association property="address" column="addressId" select="com.Aiden.dao.addressMapper.findAddressById"/>
11         <association property="company" column="companyId" select="com.Aiden.dao.companyMapper.findCompanyById"/>
12 </resultMap>

在测试类MybatisDemo02.java中添加测试方法，运行：

1 @Test
2 public void testFindPersonWithByCompanyId() {
3     logger.info("一对多关系映射——根据公司ID查询人员");
4     List<Person> person=personMapper.findPersonWithByCompanyId(1);
5     for (Person p : person) {
6         System.out.println(p);    
7     }
8 }

运行结果：

MyBatis日记（五）：一对一关系，一对多关系

 

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