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。
1 create table t_student( 2 id int primary key auto_increment, 3 student_name varchar(20) 4 ); 5 6 create table t_courses( 7 id int primary key auto_increment, 8 courses_name varchar(20) 9 ); 10 11 create table t_stu_cou( 12 id int primary key auto_increment, 13 fk_stu_id int, 14 fk_cou_id int 15 );
添加数据。
2）建立JavaBean。
CoursesBean.java
1 package com.cy.mybatis.beans;
2
3 import java.io.Serializable;
4 import java.util.List;
5 /**
6 * manyTOmany
7 * @author acer
8 *
9 */
10 public class CoursesBean implements Serializable{
11
12
13 private static final long serialVersionUID = 1L;
14 private Integer id;
15 private String name;
16 // 使用 List<StudentBean>集合，是说明学习这门课程的所有学生
17 private List<StudentBean> student;
18 public CoursesBean() {
19 super();
20 }
21 public CoursesBean(Integer id, String name, List<StudentBean> student) {
22 super();
23 this.id = id;
24 this.name = name;
25 this.student = student;
26 }
27 public Integer getId() {
28 return id;
29 }
30 public void setId(Integer id) {
31 this.id = id;
32 }
33 public String getName() {
34 return name;
35 }
36 public void setName(String name) {
37 this.name = name;
38 }
39 public List<StudentBean> getStudent() {
40 return student;
41 }
42 public void setStudent(List<StudentBean> student) {
43 this.student = student;
44 }
45 @Override
46 public String toString() {
47 return "CoursesBean [id=" + id + ", name=" + name + ", student="
48 + student + "]";
49 }
50
51
52 }
StudentBean.java
3) 定义接口
CoursesMapper.java
StudentMapper.java
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
1 <?xml version="1.0" encoding="UTF-8"?>
2 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
3 <mapper namespace="com.cy.mybatis.mapper.CoursesMapper">
4
5
6 <resultMap type="CoursesBean" id="coursesMap">
7 <!-- 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，
8 所以javaType="java.lang.Integer"可以写成javaType="Integer"-->
9
10 <id property="id" column="id" javaType="java.lang.Integer"/>
11 <result property="name" column="courses_name" javaType="java.lang.String"/>
12 </resultMap>
13
14 <resultMap type="CoursesBean" id="couAndStu">
15 <id property="id" column="id" javaType="java.lang.Integer"/>
16 <result property="name" column="courses_name" javaType="java.lang.String"/>
17
18 <!-- 对于一个属性的类型是一个集合，就使用collection
19 对于一个属性的类型是一个类，就使用association -->
20 <collection property="student" column="id" select="findStudentByCourses"></collection>
21 </resultMap>
22
23
24
25 <select id="findCouById" resultMap="coursesMap">
26 select * from t_courses where id=#{id}
27 </select>
28
29
30
31 <!-- 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。
32 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-->
33 <select id="findStudentByCourses" resultMap="com.cy.mybatis.mapper.StudentMapper.studentMap">
34 select * from t_student where id in (select fk_stu_id from t_stu_cou where fk_cou_id=#{id})
35 </select>
36
37 <select id="findCouAndStu" resultMap="couAndStu">
38 select * from t_courses where id=#{id}
39 </select>
40 </mapper>
StudentMapper.xml
5) 测试
1 package com.cy.mybatis.service;
2
3 import org.apache.ibatis.session.SqlSession;
4
5 import com.cy.mybatis.beans.CoursesBean;
6 import com.cy.mybatis.beans.StudentBean;
7 import com.cy.mybatis.mapper.CoursesMapper;
8 import com.cy.mybatis.mapper.StudentMapper;
9 import com.cy.mybatis.tools.DBTools;
10
11
12
13 public class ManyToManyService {
14
15 public static void main(String[] args) {
16
17 findStudentByCourses();
18 findCoursesByStudent();
19 }
20
21
22
23 private static void findCoursesByStudent() {
24 SqlSession session = DBTools.getSession();
25 StudentMapper sm=session.getMapper(StudentMapper.class);
26 StudentBean sb=sm.findStuAndCou(1);
27 System.out.println(sb);
28
29 }
30
31
32
33 private static void findStudentByCourses() {
34 SqlSession session = DBTools.getSession();
35 CoursesMapper cm=session.getMapper(CoursesMapper.class);
36 CoursesBean cb=cm.findCouAndStu(2);
37 System.out.println(cb);
38 }
39
40 }
结果显示：
1 DEBUG 2016-02-27 09:56:53,852 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection 2 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 586269. 3 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [[email protected]] 4 DEBUG 2016-02-27 09:56:54,070 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Preparing: select * from t_courses where id=? 5 DEBUG 2016-02-27 09:56:54,105 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 2(Integer) 6 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=?) 7 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====> Parameters: 2(Integer) 8 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==== Total: 2 9 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <== Total: 1 10 CoursesBean [id=2, name=数学, student=[StudentBean [id=1, name=米兰, courses=null], StudentBean [id=4, name=睿懿, courses=null]]] 11 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection 12 DEBUG 2016-02-27 09:56:54,136 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 23881129. 13 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [[email protected]] 14 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Preparing: select * from t_student where id = ? 15 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 1(Integer) 16 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 = ?) 17 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ====> Parameters: 1(Integer) 18 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <==== Total: 2 19 DEBUG 2016-02-27 09:56:54,152 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <== Total: 1 20 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
1 create TABLE t_pet( 2 id int primary key auto_increment, 3 name varchar(20), 4 type varchar(20), 5 bone int, 6 fish int 7 );
JavaBean
PetBean：
CatBean：
DogBean：
接口
PetMapper.java
1 package com.cy.mybatis.mapper;
2
3 import java.util.List;
4
5 import org.apache.ibatis.annotations.Param;
6
7 import com.cy.mybatis.beans.CatBean;
8 import com.cy.mybatis.beans.DogBean;
9 import com.cy.mybatis.beans.PetBean;
10
11 public interface PetMapper {
12 /**
13 * 添加宠物猫
14 * @param cat
15 * @return
16 */
17 public int saveCat(@Param("c")CatBean cat);
18
19 /**
20 * 添加宠物狗
21 * @param dog
22 * @return
23 */
24 public int saveDog(@Param("d")DogBean dog);
25
26 /**
27 * 查询所有的宠物
28 * @return
29 */
30 public List<PetBean> findAllPet();
31
32 /**
33 * 查询所有的宠物猫
34 * @return
35 */
36 public List<CatBean> findAllCat();
37
38
39 }
XML
1 <?xml version="1.0" encoding="UTF-8"?>
2 <!DOCTYPE mapper PUBLIC "-//mybatis.org/DTD Mapper 3.0" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
3 <mapper namespace="com.cy.mybatis.mapper.PetMapper">
4 <resultMap id="petMap" type="PetBean">
5 <id property="id" column="id" javaType="java.lang.Integer"/>
6 <result property="name" column="name" javaType="java.lang.String"/>
7 <!--discriminator：根据结果值决定使用哪个resultMap
8 case：判断条件
9 它的表现很像 Java 语言中的 switch 语句。
10 定义鉴别器指定了 column 和 javaType 属性
11 -->
12 <discriminator javaType="java.lang.String" column="type">
13 <case value="cat" resultType="CatBean">
14 <result property="fish" column="fish" javaType="java.lang.Integer"/>
15 </case>
16 <case value="dog" resultType="DogBean">
17 <result property="bone" column="bone" javaType="java.lang.Integer"/>
18 </case>
19 </discriminator>
20 </resultMap>
21
22 <insert id="saveCat">
23 insert into t_pet(name,type,fish) values (#{c.name},‘cat‘,#{c.fish})
24 </insert>
25 <insert id="saveDog">
26 insert into t_pet(name,type,bone) values (#{d.name},‘dog‘,#{d.bone})
27 </insert>
28
29 <select id="findAllPet" resultMap="petMap">
30 select * from t_pet
31 </select>
32 <select id="findAllCat" resultMap="petMap">
33 select * from t_pet where type = ‘cat‘
34 </select>
35
36 </mapper>
测试：
1 package com.cy.mybatis.service;
2
3 import java.util.List;
4
5 import org.apache.ibatis.session.SqlSession;
6
7 import com.cy.mybatis.beans.CatBean;
8 import com.cy.mybatis.beans.DogBean;
9 import com.cy.mybatis.beans.PetBean;
10 import com.cy.mybatis.mapper.PetMapper;
11 import com.cy.mybatis.tools.DBTools;
12
13
14
15 public class ExtendsService {
16 public static void main(String[] args) {
17 // saveCat();
18 // saveDog();
19 findAllCat();
20 findAllPet();
21 }
22
23 private static void findAllCat() {
24 // TODO Auto-generated method stub
25 SqlSession session = DBTools.getSession();
26 PetMapper pm = session.getMapper(PetMapper.class);
27 List<CatBean> cats = pm.findAllCat();
28 for (CatBean catBean : cats) {
29 System.out.println(catBean);
30 }
31 }
32
33 private static void findAllPet() {
34 // TODO Auto-generated method stub
35 SqlSession session = DBTools.getSession();
36 PetMapper pm = session.getMapper(PetMapper.class);
37 List<PetBean> pets = pm.findAllPet();
38 for (PetBean petBean : pets) {
39 System.out.println(petBean);
40 }
41 }
42
43 private static void saveDog() {
44 // TODO Auto-generated method stub
45 SqlSession session = DBTools.getSession();
46 PetMapper pm = session.getMapper(PetMapper.class);
47 DogBean dog = new DogBean(null,"哈士奇");
48 dog.setBone(10);
49 pm.saveDog(dog);
50 session.commit();
51 }
52
53 private static void saveCat() {
54 // TODO Auto-generated method stub
55 SqlSession session = DBTools.getSession();
56 PetMapper pm = session.getMapper(PetMapper.class);
57 CatBean cat = new CatBean(null,"大脸猫");
58 cat.setFish(10);
59 pm.saveCat(cat);
60 session.commit();
61 }
62 }
结果显示
1 DEBUG 2016-02-27 11:51:56,857 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection 2 DEBUG 2016-02-27 11:51:57,073 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 8768896. 3 DEBUG 2016-02-27 11:51:57,074 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [[email protected]] 4 DEBUG 2016-02-27 11:51:57,076 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Preparing: select * from t_pet where type = ‘cat‘ 5 DEBUG 2016-02-27 11:51:57,107 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 6 DEBUG 2016-02-27 11:51:57,121 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <== Total: 1 7 CatBean [fish=10, toString()=PetBean [id=1, name=大脸猫]] 8 DEBUG 2016-02-27 11:51:57,122 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Opening JDBC Connection 9 DEBUG 2016-02-27 11:51:57,133 org.apache.ibatis.datasource.pooled.PooledDataSource: Created connection 28157774. 10 DEBUG 2016-02-27 11:51:57,134 org.apache.ibatis.transaction.jdbc.JdbcTransaction: Setting autocommit to false on JDBC Connection [[email protected]] 11 DEBUG 2016-02-27 11:51:57,134 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Preparing: select * from t_pet 12 DEBUG 2016-02-27 11:51:57,134 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: ==> Parameters: 13 DEBUG 2016-02-27 11:51:57,135 org.apache.ibatis.logging.jdbc.BaseJdbcLogger: <== Total: 2 14 CatBean [fish=10, toString()=PetBean [id=1, name=大脸猫]] 15 DogBean [bone=10, toString()=PetBean [id=2, name=哈士奇]]
时间： 2024-12-09 03:06:34