MyBatis学习笔记(三) 关联关系

首先给大家推荐几个网页：

http://blog.csdn.net/isea533/article/category/2092001 没事看看 - MyBatis工具：www.mybatis.tk

http://www.mybatis.org/mybatis-3/zh/getting-started.html 入门

http://www.mybatis.tk/

http://mbg.cndocs.tk/

http://edu.51cto.com/course/course_id-1354.html  mybatis视频教程

一、多对多关系。

一般我们在设置多对多关系的时候，都是建立第三张关系表。

例子：学生t_student与课程t_courses，一个学生可以对应学习多门课程，一门课程对应可以有多名学生学习。第三张关系表t_stu_cou。

1）关系整理好，接着建立数据库表，添加信息。

 create table t_student(
  id int primary key auto_increment,
  student_name varchar(20)
 );

 create table t_courses(
 id  int primary key auto_increment,
 courses_name varchar(20)
 );

 create table t_stu_cou(
  id int primary key auto_increment,
  fk_stu_id int,
  fk_cou_id int
 );

添加数据。

 insert into t_student values (null,'米兰');
 insert into t_student values (null,'凌雪');
 insert into t_student values (null,'成成');
 insert into t_student values (null,'睿懿');
 insert into t_student values (null,'瑞瑞');

 insert into t_courses values (null,'语文');
 insert into t_courses values (null,'数学');
 insert into t_courses values (null,'计算机');
 insert into t_courses values (null,'java编程');
 insert into t_courses values (null,'html');

 insert into t_stu_cou values (null,1,1);
 insert into t_stu_cou values (null,1,2);
 insert into t_stu_cou values (null,2,3);
 insert into t_stu_cou values (null,2,4);
 insert into t_stu_cou values (null,3,1);
 insert into t_stu_cou values (null,3,5);
 insert into t_stu_cou values (null,4,4);
 insert into t_stu_cou values (null,4,2);

 2）建立JavaBean。

CoursesBean.java

 package com.cy.mybatis.beans;

 import java.io.Serializable;
 import java.util.List;
 /**
  * manyTOmany
  * @author acer
  *
  */
 public class CoursesBean implements Serializable{

     private static final long serialVersionUID = 1L;
     private Integer id;
     private String name;
    // 使用 List<StudentBean>集合，是说明学习这门课程的所有学生
     private List<StudentBean> student;
     public CoursesBean() {
         super();
     }
     public CoursesBean(Integer id, String name, List<StudentBean> student) {
         super();
         this.id = id;
         this.name = name;
         this.student = student;
     }
     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 List<StudentBean> getStudent() {
         return student;
     }
     public void setStudent(List<StudentBean> student) {
         this.student = student;
     }
     @Override
     public String toString() {
         return "CoursesBean [id=" + id + ", name=" + name + ", student="
                 + student + "]";
     }

 }

StudentBean.java

 package com.cy.mybatis.beans;

 import java.io.Serializable;
 import java.util.List;
 /**
  * manyTOmany
  * @author acer
  *
  */
 public class StudentBean implements Serializable{

     private static final long serialVersionUID = 1L;

     private Integer id;
     private String name;
     private List<CoursesBean> courses;
     public StudentBean() {
         super();
         // TODO Auto-generated constructor stub
     }
     public StudentBean(Integer id, String name, List<CoursesBean> courses) {
         super();
         this.id = id;
         this.name = name;
         this.courses = courses;
     }
     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 List<CoursesBean> getCourses() {
         return courses;
     }
     public void setCourses(List<CoursesBean> courses) {
         this.courses = courses;
     }
     @Override
     public String toString() {
         return "StudentBean [id=" + id + ", name=" + name + ", courses="
                 + courses + "]";
     }

 }

3) 定义接口  

CoursesMapper.java

 package com.cy.mybatis.mapper;

 import com.cy.mybatis.beans.CoursesBean;

 public interface CoursesMapper {

     /**
      * 根据id查询课程
      * @param id
      * @return
      */
     public CoursesBean findCouById(int id);

     /**
      * 要求查课时，将选课的学生一并查出
      * @param id
      * @return
      */
     public CoursesBean findCouAndStu(int id);

 }

StudentMapper.java

 package com.cy.mybatis.mapper;

 import com.cy.mybatis.beans.StudentBean;

 public interface StudentMapper {
     /**
      * 根据id值查询学生信息
      * @param id
      * @return
      */
     public StudentBean findStuById(int id);

     /**
      * 要求查询学生时，将学生选择的课程查出
      * @param id
      * @return
      */
     public StudentBean findStuAndCou(int id);

 }

 4) 定义xml文件。CoursesMapper.xml    StudentMapper.xml

 mybatis实际是对XML进行操作，我们所有的方法都直接定义在XML中，写个接口只是为了更好的符合我们3层的思想.XML中只要有方法，就可以使用，而调用的方式就是：namespace+方法名；

CoursesMapper.xml 

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 <mapper namespace="com.cy.mybatis.mapper.CoursesMapper">

  <resultMap type="CoursesBean" id="coursesMap">
    <!--   在默认情况下，mybatis会自动在TypeAliasRegistry初始化的时候挂在很多jdk常用类，
                           所以javaType="java.lang.Integer"可以写成javaType="Integer"-->  

     <id property="id" column="id" javaType="java.lang.Integer"/>
     <result property="name" column="courses_name" javaType="java.lang.String"/>
  </resultMap>

  <resultMap type="CoursesBean" id="couAndStu">
     <id property="id" column="id" javaType="java.lang.Integer"/>
     <result property="name" column="courses_name" javaType="java.lang.String"/>

     <!-- 对于一个属性的类型是一个集合，就使用collection
                       对于一个属性的类型是一个类，就使用association   -->
     <collection property="student" column="id" select="findStudentByCourses"></collection>
  </resultMap>

  <select id="findCouById" resultMap="coursesMap">
   select * from t_courses where id=#{id}
  </select>

  <!-- 有学生表，课程表这两张表都没有外键，我们就要使用第三张关联表。我们就要根据课程表的fk_cou_id，把学生的id值得到。
                对于多对多那么这个学生的id值就不可能是一个值 。在数据库里就要使用in-->
  <select id="findStudentByCourses" resultMap="com.cy.mybatis.mapper.StudentMapper.studentMap">
     select * from t_student where id in (select fk_stu_id from t_stu_cou where fk_cou_id=#{id})
  </select>

  <select id="findCouAndStu" resultMap="couAndStu">
  select * from t_courses where id=#{id}
  </select>
 </mapper>

StudentMapper.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 <mapper namespace="com.cy.mybatis.mapper.StudentMapper">

 <resultMap type="StudentBean" id="studentMap">
     <id property="id" column="id" javaType="java.lang.Integer"/>
     <result property="name" column="student_name" javaType="java.lang.String"/>
 </resultMap>

 <resultMap type="StudentBean" id="studentAndCourses">
      <id property="id" column="id" javaType="java.lang.Integer"/>
      <result property="name" column="student_name" javaType="java.lang.String"/>
      <collection property="courses" column="id" select="findCoursesByStudent"></collection>
 </resultMap>
     <select id="findStudentById" resultMap="studentMap">
         select * from t_student where id = #{id}
     </select>

     <select id="findStuAndCou" resultMap="studentAndCourses">
         select * from t_student where id = #{id}
     </select>
     <select id="findCoursesByStudent" resultMap="com.cy.mybatis.mapper.CoursesMapper.coursesMap">
         select * from t_courses where id in (select fk_cou_id from t_stu_cou where fk_stu_id = #{id})
     </select>

 </mapper>

 5) 测试

 package com.cy.mybatis.service;

 import org.apache.ibatis.session.SqlSession;

 import com.cy.mybatis.beans.CoursesBean;
 import com.cy.mybatis.beans.StudentBean;
 import com.cy.mybatis.mapper.CoursesMapper;
 import com.cy.mybatis.mapper.StudentMapper;
 import com.cy.mybatis.tools.DBTools;

 public class ManyToManyService {

     public static void main(String[] args) {

         findStudentByCourses();
         findCoursesByStudent();
     }

     private static void findCoursesByStudent() {
         SqlSession session = DBTools.getSession();
         StudentMapper sm=session.getMapper(StudentMapper.class);
         StudentBean sb=sm.findStuAndCou(1);
         System.out.println(sb);

     }

     private static void findStudentByCourses() {
         SqlSession session = DBTools.getSession();
         CoursesMapper cm=session.getMapper(CoursesMapper.class);
         CoursesBean cb=cm.findCouAndStu(2);
         System.out.println(cb);
     }

 }

结果显示：

 DEBUG 2016-02-27 09:56:53,852 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 586269.
 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@8f21d]
 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select * from t_courses where id=?
 DEBUG 2016-02-27 09:56:54,105 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 2(Integer)
 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====>  Preparing: select * from t_student where id in (select fk_stu_id from t_stu_cou where fk_cou_id=?)
 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====> Parameters: 2(Integer)
 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <====      Total: 2
 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 1
 CoursesBean [id=2, name=数学, student=[StudentBean [id=1, name=米兰, courses=null], StudentBean [id=4, name=睿懿, courses=null]]]
 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 23881129.
 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@16c65a9]
 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select * from t_student where id = ?
 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 1(Integer)
 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====>  Preparing: select * from t_courses where id in (select fk_cou_id from t_stu_cou where fk_stu_id = ?)
 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====> Parameters: 1(Integer)
 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <====      Total: 2
 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 1
 StudentBean [id=1, name=米兰, courses=[CoursesBean [id=1, name=语文, student=null], CoursesBean [id=2, name=数学, student=null]]]

二 、继承

最简单的例子，宠物。

数据库

 create TABLE t_pet(
 id int  primary key auto_increment,
 name varchar(20),
 type varchar(20),
 bone int,
 fish int
 );

 JavaBean

PetBean：

 package com.cy.mybatis.beans;

 import java.io.Serializable;

 public class PetBean implements Serializable {

     private static final long serialVersionUID = 8920733441991237426L;

     private Integer id;
     private String name;
     public PetBean() {
         super();
     }
     public PetBean(Integer id, String name) {
         super();
         this.id = id;
         this.name = name;

     }
     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;
     }

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

 }

CatBean：

 package com.cy.mybatis.beans;

 public class CatBean extends PetBean {

     private static final long serialVersionUID = 1978574561040340989L;

     private Integer fish;

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

     public CatBean(Integer id, String name) {
         super(id, name);
         // TODO Auto-generated constructor stub
     }

     public Integer getFish() {
         return fish;
     }
     public void setFish(Integer fish) {
         this.fish = fish;
     }

     @Override
     public String toString() {
         return "CatBean [fish=" + fish + ", toString()=" + super.toString()
                 + "]";
     }
 }

DogBean：

 package com.cy.mybatis.beans;

 public class DogBean extends PetBean {

     private static final long serialVersionUID = -9020056420879737672L;

     private Integer bone;

     public DogBean() {
         super();
     }

     public DogBean(Integer id, String name) {
         super(id, name);
     }

     public Integer getBone() {
         return bone;
     }

     public void setBone(Integer bone) {
         this.bone = bone;
     }

     @Override
     public String toString() {
         return "DogBean [bone=" + bone + ", toString()=" + super.toString()
                 + "]";
     }

 }

 

   接口

PetMapper.java

 package com.cy.mybatis.mapper;

 import java.util.List;

 import org.apache.ibatis.annotations.Param;

 import com.cy.mybatis.beans.CatBean;
 import com.cy.mybatis.beans.DogBean;
 import com.cy.mybatis.beans.PetBean;

 public interface PetMapper {
     /**
      * 添加宠物猫
      * @param cat
      * @return
      */
     public int saveCat(@Param("c")CatBean cat);

     /**
      * 添加宠物狗
      * @param dog
      * @return
      */
     public int saveDog(@Param("d")DogBean dog);

     /**
      * 查询所有的宠物
      * @return
      */
     public List<PetBean> findAllPet();

     /**
      * 查询所有的宠物猫
      * @return
      */
     public List<CatBean> findAllCat();

 }

 XML

 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
 <mapper namespace="com.cy.mybatis.mapper.PetMapper">
     <resultMap id="petMap" type="PetBean">
         <id property="id" column="id" javaType="java.lang.Integer"/>
         <result property="name" column="name" javaType="java.lang.String"/>
         <!--discriminator：根据结果值决定使用哪个resultMap
             case：判断条件
                           它的表现很像 Java 语言中的 switch 语句。
                           定义鉴别器指定了 column 和 javaType 属性
             -->
         <discriminator javaType="java.lang.String" column="type">
             <case value="cat" resultType="CatBean">
                 <result property="fish" column="fish" javaType="java.lang.Integer"/>
             </case>
             <case value="dog" resultType="DogBean">
                 <result property="bone" column="bone" javaType="java.lang.Integer"/>
             </case>
         </discriminator>
     </resultMap>

     <insert id="saveCat">
         insert into t_pet(name,type,fish) values (#{c.name},'cat',#{c.fish})
     </insert>
     <insert id="saveDog">
         insert into t_pet(name,type,bone) values (#{d.name},'dog',#{d.bone})
     </insert>

     <select id="findAllPet" resultMap="petMap">
         select * from t_pet
     </select>
     <select id="findAllCat" resultMap="petMap">
         select * from t_pet where type = 'cat'
     </select>

 </mapper>

测试：

 package com.cy.mybatis.service;

 import java.util.List;

 import org.apache.ibatis.session.SqlSession;

 import com.cy.mybatis.beans.CatBean;
 import com.cy.mybatis.beans.DogBean;
 import com.cy.mybatis.beans.PetBean;
 import com.cy.mybatis.mapper.PetMapper;
 import com.cy.mybatis.tools.DBTools;

 public class ExtendsService {
     public static void main(String[] args) {
 //        saveCat();
 //        saveDog();
         findAllCat();
         findAllPet();
     }

     private static void findAllCat() {
         // TODO Auto-generated method stub
         SqlSession session = DBTools.getSession();
         PetMapper pm = session.getMapper(PetMapper.class);
         List<CatBean> cats = pm.findAllCat();
         for (CatBean catBean : cats) {
             System.out.println(catBean);
         }
     }

     private static void findAllPet() {
         // TODO Auto-generated method stub
         SqlSession session = DBTools.getSession();
         PetMapper pm = session.getMapper(PetMapper.class);
         List<PetBean> pets = pm.findAllPet();
         for (PetBean petBean : pets) {
             System.out.println(petBean);
         }
     }

     private static void saveDog() {
         // TODO Auto-generated method stub
         SqlSession session = DBTools.getSession();
         PetMapper pm = session.getMapper(PetMapper.class);
         DogBean dog = new DogBean(null,"哈士奇");
         dog.setBone(10);
         pm.saveDog(dog);
         session.commit();
     }

     private static void saveCat() {
         // TODO Auto-generated method stub
         SqlSession session = DBTools.getSession();
         PetMapper pm = session.getMapper(PetMapper.class);
         CatBean cat = new CatBean(null,"大脸猫");
         cat.setFish(10);
         pm.saveCat(cat);
         session.commit();
     }
 }

结果显示

 DEBUG 2016-02-27 11:51:56,857 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
 DEBUG 2016-02-27 11:51:57,073 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 8768896.
 DEBUG 2016-02-27 11:51:57,074 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@85cd80]
 DEBUG 2016-02-27 11:51:57,076 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select * from t_pet where type = 'cat'
 DEBUG 2016-02-27 11:51:57,107 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters:
 DEBUG 2016-02-27 11:51:57,121 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 1
 CatBean [fish=10, toString()=PetBean [id=1, name=大脸猫]]
 DEBUG 2016-02-27 11:51:57,122 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection
 DEBUG 2016-02-27 11:51:57,133 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 28157774.
 DEBUG 2016-02-27 11:51:57,134 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@1ada74e]
 DEBUG 2016-02-27 11:51:57,134 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==>  Preparing: select * from t_pet
 DEBUG 2016-02-27 11:51:57,134 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters:
 DEBUG 2016-02-27 11:51:57,135 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==      Total: 2
 CatBean [fish=10, toString()=PetBean [id=1, name=大脸猫]]
 DogBean [bone=10, toString()=PetBean [id=2, name=哈士奇]]