mybatis中一对一，一对多，多对多的关系

时间：2021-10-01 11:59:10

首先 创建好项目 然后导入依赖：

<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.12</version>
  <scope>test</scope>
</dependency>

<dependency>
  <groupId>org.mybatis</groupId>
  <artifactId>mybatis</artifactId>
  <version>3.4.5</version>
</dependency>
<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.43</version>
</dependency>


然后，再加入一些配置信息，加载java文件夹下下面的xml文件：
<build>
  <finalName>g160828_mybatis01</finalName>

  <resources>
    <resource>
      <directory>src/main/java</directory>
      <includes>
        <include>**/*.xml</include>
      </includes>
    </resource>
  </resources>


</build


一：一对一

1.先说一下 一对一的关系：

我的Person类与Card类：

Person：

private String pname;
private int pid;
private int page;

private Card card;  //一对一
 

Card类：



 

private int uid;
private String cnumber;
 

 

 

 

然后，再是我的dao接口一个方法：
 

public Person getPersonandCard(int pid);
 

 

 

2.然后，在生成person.xml，这里我就把card.xml浓缩在person.xml里面去了：
 

 

<?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.desert.Dao.IPersonDao">



<resultMap id="myPersonMap" type="com.desert.entity.Person">
    <id property="pid" column="pid"></id>
    <result property="pname" column="pname"></result>
    <result property="page" column="page"></result>
    <association property="card" javaType="com.desert.entity.Card">
        <id property="uid" column="uid"></id>
        <result property="cnumber" column="cnumber"></result>
    </association>
</resultMap>

 

 

<!--我这里就做一个示列，根据id得到人和卡-->
<select id="getPersonandCard" resultMap="myPersonMap" parameterType="int">
    select p.*,c.cnumber from person p,card c where p.pid=c.uid and p.pid=#{pid}
</select>

</mapper>





 

3.再是配置我的mybatis-config.xml文件：
 

 

<?xml version="1.0" encoding="UTF-8" ?>
        <!DOCTYPE configuration  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-config.dtd">  <configuration>

<!--设置别名--> <typeAliases>
    <!--<typeAlias type="com.desert.Dto.MyPerson" alias="a"></typeAlias>-->  <package name="com.desert"></package>
</typeAliases>

<environments default="development">
    <environment id="development">
        <transactionManager type="JDBC"/>
        <dataSource type="POOLED">
            <property name="driver" value="com.mysql.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://localhost:3306/test"/>
            <property name="username" value="root"/>
            <property name="password" value="root"/>
        </dataSource>
    </environment>
</environments>
<mappers>
    <mapper resource="com/desert/entity/person.xml"/>
</mappers>
</configuration>

 

4.测试： 

 

SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config"));

//通过sessionFactory获得SqlSession SqlSession sqlSession=sqlSessionFactory.openSession();



IPersonDao iPersonDao=sqlSession.getMapper(IPersonDao.class);
 

//根据id得到Person和它的Card
Person person=iPersonDao.getPersonandCard(1);
System.out.println(person+","+person.getCard());
 

sqlSession.close();
 

 

 

二：一对多：
 

一对多 ，我就拿一个省份和城市这个关系来说吧：
 

首先：是我的省份表：
 

Provinces：
 

 

private int pid;
private String pname;

private Set<Citys> citysSet;
然后，再是我的城市表： 

City：
 

 

private int cid;
private String cname;
private int pid;
 

 

然后，再是我的dao接口一个方法：
 

 

 

public Provinces getProvinces(int pid);
 



然后，再是我的person.xml文件关于多对多的关系：
 

 

<resultMap id="myProvincesMap" type="com.desert.entity.Provinces">
    <id property="pid" column="pid"></id>
    <result property="pname" column="pname"></result>
    <collection property="citysSet" ofType="com.desert.entity.Citys">
        <id property="cid" column="cid"></id>
        <result property="cname" column="cname"></result>
        <result property="pid" column="pid"></result>
    </collection>
</resultMap>

 

<!--我这里就是根据id得到一个省份，然后再点出这个省份下面的城市-->
 

 

<select id="getProvinces" resultMap="myProvincesMap" parameterType="int">
    select p.*,c.cname from provinces p,citys c where p.pid=c.pid and p.pid=#{pid}
</select>
 

然后，再去测试就好了： 

 

try {
 

     //加载配置文件
    SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config"));

    //通过sessionFactory获得SqlSession  SqlSession sqlSession=sqlSessionFactory.openSession();



    //根据id得到省份，然后通过省份点出城市：
 

    IPersonDao iPersonDao=sqlSession.getMapper(IPersonDao.class);
    Provinces provinces=iPersonDao.getProvinces(1);
    System.out.println(provinces.getPname());
 for (Citys citys : provinces.getCitysSet()) {
    System.out.println(citys.getCname());
    }
 

  sqlSession.close();



} catch (IOException e) {
    e.printStackTrace();
}
 


 


 

三：多对多的关系：
 

多对多的关系我就以Users和Roles用户和角色来演示：
 

Users表：
 

 

private int uid;
private String uname;

private Set<Roles> roles;
 

 

Roles表：
 

 

private int rid;
private String rname;

private Set<Users> users;
 

然后，再是我的users.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.desert.Dao.IUsersDao">

    <resultMap type="com.desert.entity.Users" id="usersMap">
        <id property="uid" column="uid" />
        <result property="uname" column="uname" />

    </resultMap>

    <resultMap type="com.desert.entity.Users" id="usersRolesMap" extends="usersMap">
        <collection property="roles" ofType="com.desert.entity.Roles">
            <id property="rid" column="rid" />
            <result property="rname" column="rname" />
        </collection>
    </resultMap>

    <select id="selectAllUser" resultMap="usersMap">
        select * from users
    </select>

    <select id="selectusersRoles" parameterType="int" resultMap="usersRolesMap">
       select u.uid,u.uname,r.rid,r.rname  from users u left join u_r ur on u.uid=ur.uid  left join roles r on ur.rid=r.rid where u.uid =#{uid}
    </select>
    
</mapper>



再者，是我的roles.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.desert.Dao.IRolesDao">

    <resultMap type="com.desert.entity.Roles" id="rolesMap">
        <id property="rid" column="rid" />
        <result property="rname" column="rname" />
    </resultMap>

    <resultMap type="com.desert.entity.Roles" id="rolesUsersMap" extends="rolesMap">
        <collection property="users" ofType="com.desert.entity.Users">
            <id property="uid" column="uid" />
            <result property="uname" column="uname" />
        </collection>
    </resultMap>

    <select id="selectAllRoles" resultMap="rolesMap">
        select * from roles
    </select>

</mapper>
 



 

3.接下来就是我的dao层接口：
 

//根据id得到用户，然后再通过用户点出该用户的所有接口：
 

 

public Users selectusersRoles(int uid);




 

4.然后，去mybatisj-config.xml加载这个xml文件：
 

<?xml version="1.0" encoding="UTF-8" ?>
        <!DOCTYPE configuration  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"  "http://mybatis.org/dtd/mybatis-3-config.dtd">  <configuration>

<!--设置别名--> <typeAliases>
    <!--<typeAlias type="com.desert.Dto.MyPerson" alias="a"></typeAlias>-->  <package name="com.desert"></package>
</typeAliases>

<environments default="development">
    <environment id="development">
        <transactionManager type="JDBC"/>
        <dataSource type="POOLED">
            <property name="driver" value="com.mysql.jdbc.Driver"/>
            <property name="url" value="jdbc:mysql://localhost:3306/test"/>
            <property name="username" value="root"/>
            <property name="password" value="root"/>
        </dataSource>
    </environment>
</environments>
<mappers>
    <mapper resource="com/desert/entity/users.xml"/>
    <mapper resource="com/desert/entity/roles.xml"/>
</mappers>
</configuration>




 

5.现在，就可以开始测试了：
 

 

try {
    SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(Resources.getResourceAsStream("mybatis-config"));

    //通过sessionFactory获得SqlSession  SqlSession sqlSession=sqlSessionFactory.openSession();
 

    IUsersDao iUsersDao=sqlSession.getMapper(IUsersDao.class);
 

    //通过根据id得到用户
    Users users= (Users) iUsersDao.selectusersRoles(1);
    System.out.println("用户名"+users.getUname());
 

     //点出所有的角色：
 for (Roles roles : users.getRoles()) {
       System.out.println("角色名："+roles.getRname());
   }
 

 

 

   sqlSession.close();

} catch (IOException e) {
    e.printStackTrace();
}
 

 

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