（四）MyBatis关系映射

第一节：一对一关系实现

需要实现一对一的关系，首先我们有两张表，t-addree和t_student。

 CREATE TABLE `t_address` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `sheng` varchar(20) DEFAULT NULL,
   `shi` varchar(20) DEFAULT NULL,
   `qu` varchar(20) DEFAULT NULL,
   PRIMARY KEY (`id`)
 ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

 insert  into `t_address`(`id`,`sheng`,`shi`,`qu`) values (1,'江苏省','苏州市','姑苏区'),(2,'江苏省','南京市','鼓楼区');

 CREATE TABLE `t_student` (
   `id` int(11) NOT NULL AUTO_INCREMENT,
   `name` varchar(20) DEFAULT NULL,
   `age` int(11) DEFAULT NULL,
   `addressId` int(11) DEFAULT NULL,
   PRIMARY KEY (`id`)
 ) ENGINE=InnoDB AUTO_INCREMENT=8 DEFAULT CHARSET=utf8;

 insert  into `t_student`(`id`,`name`,`age`,`addressId`) values (1,'张三',10,1),(2,'李四',11,2),(3,'李四',11,2),(4,'李四',11,2),(5,'李四',11,2),(6,'李四',11,2),(7,'李四',11,2);

然后写model层

Address.java

 package com.javaxk.model;

 public class Address {

     private Integer id;
     private String sheng;
     private String shi;
     private String qu;

     public Integer getId() {
         return id;
     }
     public void setId(Integer id) {
         this.id = id;
     }
     public String getSheng() {
         return sheng;
     }
     public void setSheng(String sheng) {
         this.sheng = sheng;
     }
     public String getShi() {
         return shi;
     }
     public void setShi(String shi) {
         this.shi = shi;
     }
     public String getQu() {
         return qu;
     }
     public void setQu(String qu) {
         this.qu = qu;
     }
     @Override
     public String toString() {
         return "Address [id=" + id + ", sheng=" + sheng + ", shi=" + shi
                 + ", qu=" + qu + "]";
     }

 }

Student.java

 package com.javaxk.model;

 public class Student {

     private Integer id;
     private String name;
     private Integer age;
     private Address address;

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

     public Student(Integer id, String name, Integer age) {
         super();
         this.id = id;
         this.name = name;
         this.age = age;
     }

     public Student(String name, Integer age) {
         super();
         this.name = name;
         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 Integer getAge() {
         return age;
     }
     public void setAge(Integer age) {
         this.age = age;
     }
     public Address getAddress() {
         return address;
     }

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

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

 }

mappers映射类

AddressMapper.java

 package com.javaxk.mappers;

 import com.javaxk.model.Address;

 public interface AddressMapper {

     public Address findById(Integer id);

 }

StudentMapper.java

 package com.javaxk.mappers;

 import java.util.List;

 import com.javaxk.model.Student;

 public interface StudentMapper {

     public Student findStudentWithAddress(Integer id);
 }

主程序运行类

StudentTest3.java

 package com.javaxk.service;

 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.javaxk.mappers.StudentMapper;
 import com.javaxk.model.Student;
 import com.javaxk.util.SqlSessionFactoryUtil;

 public class StudentTest3 {

     private static Logger logger=Logger.getLogger(StudentTest.class);
     private SqlSession sqlSession=null;
     private StudentMapper studentMapper=null;

     /**
      * 测试方法前调用
      * @throws Exception
      */
     @Before
     public void setUp() throws Exception {
         sqlSession=SqlSessionFactoryUtil.openSession();
         studentMapper=sqlSession.getMapper(StudentMapper.class);
     }

     /**
      * 测试方法后调用
      * @throws Exception
      */
     @After
     public void tearDown() throws Exception {
         sqlSession.close();
     }

     @Test
     public void testFindStudentWithAddress() {
         logger.info("查询学生(带地址)");
         Student student=studentMapper.findStudentWithAddress(1);
         System.out.println(student);
     }

 }

Mapper映射文件的不同写法。。。

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.javaxk.mappers.AddressMapper">

     <resultMap type="Address" id="AddressResult">
         <result property="id" column="id"/>
         <result property="sheng" column="sheng"/>
         <result property="shi" column="shi"/>
         <result property="qu" column="qu"/>
     </resultMap>

     <select id="findById" parameterType="Integer" resultType="Address">
         select * from t_address where id=#{id}
     </select>

 </mapper> 

第一种方式：

 <?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.javaxk.mappers.StudentMapper">

     <resultMap type="Student" id="StudentResult">
         <id property="id" column="id"/>
         <result property="name" column="name"/>
         <result property="age" column="age"/>

         <result property="address.id" column="addressId"/>
         <result property="address.sheng" column="sheng"/>
         <result property="address.shi" column="shi"/>
         <result property="address.qu" column="qu"/>
     </resultMap>
     <select id="findStudentWithAddress" resultMap="StudentResult" parameterType="Integer">
         select * from t_student t1,t_address t2 where t1.addressId=t2.id and t1.id=#{id}
     </select>
 </mapper> 

第二种方式：

 <?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.javaxk.mappers.StudentMapper">
 <resultMap type="Address" id="AddressResult">
         <result property="id" column="id"/>
         <result property="sheng" column="sheng"/>
         <result property="shi" column="shi"/>
         <result property="qu" column="qu"/>
 </resultMap>

 <resultMap type="Student" id="StudentResult">
         <id property="id" column="id"/>
         <result property="name" column="name"/>
         <result property="age" column="age"/>
         <association property="address" resultMap="AddressResult"/>
 </resultMap>

 <select id="findStudentWithAddress" resultMap="StudentResult" parameterType="Integer">
         select * from t_student t1,t_address t2 where t1.addressId=t2.id and t1.id=#{id}
     </select>
 </mapper> 

第三种方式：

 <?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.javaxk.mappers.StudentMapper">
      <resultMap type="Student" id="StudentResult">
         <id property="id" column="id"/>
         <result property="name" column="name"/>
         <result property="age" column="age"/>
         <association property="address" javaType="Address">
             <result property="id" column="id"/>
             <result property="sheng" column="sheng"/>
             <result property="shi" column="shi"/>
             <result property="qu" column="qu"/>
         </association>
     </resultMap> 

     <select id="findStudentWithAddress" resultMap="StudentResult" parameterType="Integer">
         select * from t_student t1,t_address t2 where t1.addressId=t2.id and t1.id=#{id}
     </select>

 </mapper> 

第四种方式：

 <?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.javaxk.mappers.StudentMapper">
     <resultMap type="Student" id="StudentResult">
         <id property="id" column="id"/>
         <result property="name" column="name"/>
         <result property="age" column="age"/>
         <association property="address" column="id" select="com.javaxk.mappers.AddressMapper.findById"></association>
     </resultMap>

     <select id="findStudentWithAddress" resultMap="StudentResult" parameterType="Integer">
         select * from t_student t1,t_address t2 where t1.addressId=t2.id and t1.id=#{id}
     </select>

 </mapper> 

第二节：一对多关系实现

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="com.javaxk.mappers.StudentMapper">

     <resultMap type="Student" id="StudentResult">
         <id property="id" column="id"/>
         <result property="name" column="name"/>
         <result property="age" column="age"/>
         <association property="address" column="addressId" select="com.javaxk.mappers.AddressMapper.findById"></association>
         <association property="grade" column="gradeId" select="com.javaxk.mappers.GradeMapper.findById"></association>
     </resultMap>

     <select id="findStudentWithAddress" resultMap="StudentResult" parameterType="Integer">
         select * from t_student t1,t_address t2 where t1.addressId=t2.id and t1.id=#{id}
     </select>

 </mapper> 

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.javaxk.mappers.AddressMapper">

     <resultMap type="Address" id="AddressResult">
         <result property="id" column="id"/>
         <result property="sheng" column="sheng"/>
         <result property="shi" column="shi"/>
         <result property="qu" column="qu"/>
     </resultMap>

     <select id="findById" parameterType="Integer" resultType="Address">
         select * from t_address where id=#{id}
     </select>

 </mapper> 

GradeMapper.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.javaxk.mappers.GradeMapper">

     <resultMap type="Grade" id="GradeResult">
         <result property="id" column="id"/>
         <result property="gradeName" column="gradeName"/>

     </resultMap>

     <select id="findById" parameterType="Integer" resultType="Grade">
         select * from t_grade where id=#{id}
     </select>

 </mapper> 

测试主类：

     @Test
     public void testFindStudentWithGrade(){
         logger.info("查询学生(带年级)");
         Student student=studentMapper.findStudentWithAddress(1);
         System.out.println(student);
     }