MyBatis日記（五）：一對一關係，一對多關係

一對一關係：

首先在數據庫中新增地址表（t_address）用於存儲人員的地址信息：

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

而後在人員信息表（t_person）中增長addressId字段：

 1 ALTER TABLE t_person ADD addressId int(11); 

在com.Aiden.domain中新增地址信息的實體類（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 [id=" + id + ", country=" + country + ", city=" + city + ", district=" + district + "]"; 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實體類中增長address屬性並添加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包中建立新的Junit測試類（MyBatisDemo02.Java），並添加測試方法：

 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  * 一對1、一對多關係映射 18  * @author 郭祥躍 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("一對多關係映射"); 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  * 根據ID查詢人員及地址信息 3  * @param id 4  * @return
5  */
6 public List<Person> findPersonWithAddressById(Integer id);

在personMapper.xml文件中添加select查詢：

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返回結果：此處resultMap標籤有幾種不一樣的實現，記之以下：

第一種：

 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>

查詢結果：

 

第二種：

 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>

查詢結果：

 

第三種：

 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>

查詢結果：

 

第四種(最經常使用)：

這種方法藉助於Address的查詢方法進行實現：

首先在addressMapper.java接口文件中，添加查詢的接口：

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

而後在addressMapper.xml中添加select標籤：

 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爲：

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>

查詢結果：

 

 

 

一對多關係：

簡單的說一對多的關係能夠用多個一對一關係實現。

首先在數據庫中新增公司信息表（t_company）用於存儲人員的地址信息：

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

而後在人員信息表（t_person）中增長addressId字段：

 1 ALTER TABLE t_person ADD companyId int(11); 

在com.Aiden.domain中新增公司信息的實體類（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 [id=" + id + ", companyName=" + companyName + "]"; 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  * 根據ID查詢公司詳情  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實體類中添加company屬性及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中添加新的查詢接口：

/** * 根據公司Id查詢人員信息 * @param id * @return
 */
public List<Person> findPersonWithByCompanyId(Integer companyId);

在personMapper.xml添加查詢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>

在測試類MybatisDemo02.java中添加測試方法，運行：

1 @Test 2 public void testFindPersonWithByCompanyId() { 3     logger.info("一對多關係映射——根據公司ID查詢人員"); 4     List<Person> person=personMapper.findPersonWithByCompanyId(1); 5     for (Person p : person) { 6  System.out.println(p); 7  } 8 }

運行結果：