【MyBatis】MyBatis 多表操作

MyBatis 多表操作

文章源码

一对一查询

需求：查询所有账户信息，关联查询下单用户信息。

注意：因为一个账户信息只能供某个用户使用，所以从查询账户信息出发关联查询用户信息为一对一查询。如果从用户信息出发关联查询用户下的账户信息则为一对多查询，因为一个用户可以有多个账户。

可以使用 resultMap，定义专门的 resultMap 用于映射一对一查询结果。

• 定义账户信息的数据表

  DROP TABLE IF EXISTS `account`;
  
  CREATE TABLE `account` (
                          `ID` int(11) NOT NULL COMMENT '编号',
                          `UID` int(11) default NULL COMMENT '用户编号',
                          `MONEY` double default NULL COMMENT '金额',
                          PRIMARY KEY  (`ID`),
                          KEY `FK_Reference_8` (`UID`),
                          CONSTRAINT `FK_Reference_8` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
  
  insert  into `account`(`ID`,`UID`,`MONEY`) values (1,41,1000),(2,45,1000),(3,41,2000);
  

• 定义账户信息的实体类

  package cn.parzulpan.domain;
  
  import java.io.Serializable;
  
  /**
  * @Author : parzulpan
  * @Time : 2020-12
  * @Desc :
  */
  
  public class Account implements Serializable {
      private Integer id;
      private Integer uid;
      private Double money;
      private User user;
  
      public Integer getId() {
          return id;
      }
  
      public void setId(Integer id) {
          this.id = id;
      }
  
      public Integer getUid() {
          return uid;
      }
  
      public void setUid(Integer uid) {
          this.uid = uid;
      }
  
      public Double getMoney() {
          return money;
      }
  
      public void setMoney(Double money) {
          this.money = money;
      }
  
      public User getUser() {
          return user;
      }
  
      public void setUser(User user) {
          this.user = user;
      }
  
      @Override
      public String toString() {
          return "Account{" +
                  "id=" + id +
                  ", uid=" + uid +
                  ", money=" + money +
                  ", user=" + user +
                  '}';
      }
  }
  

• 编写 SQL

  select u.*, a.id as aid, a.uid, a.money
  from account a, user u
  where a.uid = u.id;
  

• 定义账户的持久层 DAO 接口

  package cn.parzulpan.dao;
  
  import cn.parzulpan.domain.Account;
  
  import java.util.List;
  
  /**
  * @Author : parzulpan
  * @Time : 2020-12
  * @Desc :
  */
  
  public interface AccountDAO {
  
      /**
      * 查询所有账户，同时获取账户的所属用户名称以及它的地址信息
      * @return
      */
      List<Account> findAll();
  }
  

• 配置 AccountDAO.xml 文件

  <?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="cn.parzulpan.dao.AccountDAO">
  
      <!-- 建立对应关系 -->
      <resultMap id="accountMap" type="account">
          <id column="aid" property="id"/>
          <result column="uid" property="uid"/>
          <result column="money" property="money"/>
  
          <!-- 用于指定从数据表方的引用实体属性 -->
          <association property="user" javaType="user">
              <id column="id" property="id"/>
              <result column="username" property="username"/>
              <result column="sex" property="sex"/>
              <result column="birthday" property="birthday"/>
              <result column="address" property="address"/>
          </association>
      </resultMap>
  
      <select id="findAll" resultMap="accountMap">
          select u.*, a.id as aid, a.uid, a.money
          from account a, user u
          where a.uid = u.id;
      </select>
  </mapper>
  

• 测试

  package cn.parzulpan.test;
  
  import cn.parzulpan.dao.AccountDAO;
  import cn.parzulpan.domain.Account;
  import org.apache.ibatis.io.Resources;
  import org.apache.ibatis.session.SqlSession;
  import org.apache.ibatis.session.SqlSessionFactory;
  import org.apache.ibatis.session.SqlSessionFactoryBuilder;
  import org.junit.After;
  import org.junit.Before;
  import org.junit.Test;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.List;
  
  /**
  * @Author : parzulpan
  * @Time : 2020-12
  * @Desc : 多表查询
  */
  
  public class MyBatisQueryTest {
      private InputStream is;
      SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
      private SqlSessionFactory factory;
      private SqlSession session;
      private AccountDAO accountDAO;
  
      @Before
      public void init() throws IOException {
          is = Resources.getResourceAsStream("SqlMapConfig.xml");
          factory = builder.build(is);
          session = factory.openSession();
          accountDAO = session.getMapper(AccountDAO.class);
      }
  
      @After
      public void destroy() throws IOException {
          session.commit();   // 事务提交
          session.close();
          is.close();
      }
  
      @Test
      public void findAllTest() {
          List<Account> accounts = accountDAO.findAll();
          for (Account account : accounts) {
              System.out.println(account);
              System.out.println(account.getUser());
          }
      }
  }
  
  

一对多查询

需求：查询所有用户信息及用户关联的账户信息。

分析：用户信息和他的账户信息为一对多关系，并且查询过程中如果用户没有账户信息，此时也要将用户信息查询出来，所以左外连接查询比较合适。

• 编写 SQL

  select u.*, a.id as id, a.uid, a.money
  from user u left join account a on u.id = a. uid;
  

• User 类加入 List<Account>

• 用户持久层 DAO 接口中加入查询方法

  /**
  * 查询所有用户，同时获取出每个用户下的所有账户信息
  * @return
  */
  List<User> findAllAndAccount();
  

• 配置 UserDAO.xml 文件

      <resultMap id="userMap" type="user">
          <id column="id" property="id"/>
          <result column="username" property="username"/>
          <result column="address" property="address"/>
          <result column="sex" property="sex"/>
          <result column="birthday" property="birthday"/>
  
          <!-- collection 是用于建立一对多中集合属性的对应关系 ofType 用于指定集合元素的数据类型 -->
          <collection property="accounts" ofType="account">
              <id column="aid" property="id"/>
              <result column="uid" property="uid"/>
              <result column="money" property="money"/>
          </collection>
      </resultMap>
  
      <select id="findAllAndAccount" resultMap="userMap">
          select u.*, a.id as aid, a.uid, a.money
          from user u left join account a on u.id = a. uid;
      </select>
  

• 测试

  @Test
  public void findAllAndAccountTest() {
      List<User> users = userDAO.findAllAndAccount();
      for (User user : users) {
          System.out.println();
          System.out.println("----- " + user.getUsername() + " -----");
          System.out.println(user);
          System.out.println(user.getAccounts());
      }
  }
  

多对多查询

需求：实现查询所有对象并且加载它所分配的用户信息。

注意：查询角色我们需要用到Role表，但角色分配的用户的信息我们并不能直接找到用户信息，而是要通过中间表（USER_ROLE 表）才能关联到用户信息。

• 定义相关的数据表

  # -----
  
  DROP TABLE IF EXISTS `role`;
  
  CREATE TABLE `role` (
                          `ID` int(11) NOT NULL COMMENT '编号',
                          `ROLE_NAME` varchar(30) default NULL COMMENT '角色名称',
                          `ROLE_DESC` varchar(60) default NULL COMMENT '角色描述',
                          PRIMARY KEY  (`ID`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
  
  insert  into `role`(`ID`,`ROLE_NAME`,`ROLE_DESC`) values (1,'院长','管理整个学院'),(2,'总裁','管理整个公司'),(3,'校长','管理整个学校');
  
  # -----
  
  DROP TABLE IF EXISTS `user_role`;
  
  CREATE TABLE `user_role` (
                              `UID` int(11) NOT NULL COMMENT '用户编号',
                              `RID` int(11) NOT NULL COMMENT '角色编号',
                              PRIMARY KEY  (`UID`,`RID`),
                              KEY `FK_Reference_10` (`RID`),
                              CONSTRAINT `FK_Reference_10` FOREIGN KEY (`RID`) REFERENCES `role` (`ID`),
                              CONSTRAINT `FK_Reference_9` FOREIGN KEY (`UID`) REFERENCES `user` (`id`)
  ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
  
  insert  into `user_role`(`UID`,`RID`) values (41,1),(45,1),(41,2);
  

• 定义角色信息的实体类

  package cn.parzulpan.domain;
  
  import java.io.Serializable;
  import java.util.List;
  
  /**
  * @Author : parzulpan
  * @Time : 2020-12
  * @Desc : 角色实体类
  */
  
  public class Role implements Serializable {
      private Integer roleId;
      private String roleName;
      private String roleDesc;
  
      private List<User> users;   //多对多的关系映射：一个角色可以赋予多个用户
  
      public Integer getRoleId() {
          return roleId;
      }
  
      public void setRoleId(Integer roleId) {
          this.roleId = roleId;
      }
  
      public String getRoleName() {
          return roleName;
      }
  
      public void setRoleName(String roleName) {
          this.roleName = roleName;
      }
  
      public String getRoleDesc() {
          return roleDesc;
      }
  
      public void setRoleDesc(String roleDesc) {
          this.roleDesc = roleDesc;
      }
  
      public List<User> getUsers() {
          return users;
      }
  
      public void setUsers(List<User> users) {
          this.users = users;
      }
  
      @Override
      public String toString() {
          return "Role{" +
                  "roleId=" + roleId +
                  ", roleName='" + roleName + '\'' +
                  ", roleDesc='" + roleDesc + '\'' +
                  ", users=" + users +
                  '}';
      }
  }
  

• 编写 RoleDAO 持久层接口

  package cn.parzulpan.dao;
  
  import cn.parzulpan.domain.Role;
  
  import java.util.List;
  
  /**
  * @Author : parzulpan
  * @Time : 2020-12
  * @Desc :
  */
  
  public interface RoleDAO {
  
      /**
      * 查询所有角色
      * @return
      */
      List<Role> findAll();
  }
  
  

• 编写映射文件

  <?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="cn.parzulpan.dao.RoleDAO">
  
      <!-- 建立对应关系 -->
      <resultMap id="roleMap" type="role">
          <id property="roleId" column="rid"/>
          <result property="roleName" column="role_name"/>
          <result property="roleDesc" column="role_desc"/>
          <collection property="users" ofType="user">
              <id column="id" property="id"/>
              <result column="username" property="username"/>
              <result column="address" property="address"/>
              <result column="sex" property="sex"/>
              <result column="birthday" property="birthday"/>
          </collection>
      </resultMap>
  
      <select id="findAll" resultMap="roleMap">
          select r.id as rid, r.role_name, r.role_desc, u.*
          from role r left outer join user_role ur on r.id = ur.rid left outer join user u on u.id = ur.uid
      </select>
  </mapper>
  

• 测试

  package cn.parzulpan.test;
  
  import cn.parzulpan.dao.AccountDAO;
  import cn.parzulpan.dao.RoleDAO;
  import cn.parzulpan.domain.Account;
  import cn.parzulpan.domain.Role;
  import cn.parzulpan.domain.User;
  import org.apache.ibatis.io.Resources;
  import org.apache.ibatis.session.SqlSession;
  import org.apache.ibatis.session.SqlSessionFactory;
  import org.apache.ibatis.session.SqlSessionFactoryBuilder;
  import org.junit.After;
  import org.junit.Before;
  import org.junit.Test;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.util.List;
  
  /**
  * @Author : parzulpan
  * @Time : 2020-12
  * @Desc : 多表查询
  */
  
  public class MyBatisManyQueryTest {
      private InputStream is;
      SqlSessionFactoryBuilder builder = new SqlSessionFactoryBuilder();
      private SqlSessionFactory factory;
      private SqlSession session;
      private RoleDAO roleDAO;
  
      @Before
      public void init() throws IOException {
          is = Resources.getResourceAsStream("SqlMapConfig.xml");
          factory = builder.build(is);
          session = factory.openSession();
          roleDAO = session.getMapper(RoleDAO.class);
      }
  
      @After
      public void destroy() throws IOException {
          session.commit();   // 事务提交
          session.close();
          is.close();
      }
  
      @Test
      public void findAllTest() {
          List<Role> roles = roleDAO.findAll();
          for (Role role : roles) {
              System.out.println();
              System.out.println("----- " +  " -----");
              System.out.println(role);
              if (role != null) {
                  System.out.println(role.getUsers());
              }
          }
      }
  }
  

练习和总结