（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);

     }

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（四）MyBatis关系映射

第一节：一对一关系实现

第二节：一对多关系实现

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