03 mybatis多表查询一对一，一对多, 多对多

版权声明：转载需经过作者同意，请尊重原创 https://blog.csdn.net/woshilovetg/article/details/85386361

Account.java

package cn.itcast.domin; public class Account {     private Integer aid;     private Integer uid;     private Double money;     //实现一对一     private User user;     public User getUser() {         return user;     }     public void setUser(User user) {         this.user = user;     }     public Account() {     }     public Integer getAid() {         return aid;     }     public void setAid(Integer aid) {         this.aid = aid;     }     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;     }     @Override     public String toString() {         return "Account{" +                 "aid=" + aid +                 ", uid=" + uid +                 ", money=" + money +                 '}';     } }

User.java

package cn.itcast.domin; import java.io.Serializable; import java.util.Date; import java.util.List; /**  *  */ public class User implements Serializable {     private Integer userId;     private String userName;     private String userAddress;     private String userSex;     private Date userBirthday;     //实现一对多     private List<Account> accounts;     public List<Account> getAccounts() {         return accounts;     }     public void setAccounts(List<Account> accounts) {         this.accounts = accounts;     }     public Integer getUserId() {         return userId;     }     public void setUserId(Integer userId) {         this.userId = userId;     }     public String getUserName() {         return userName;     }     public void setUserName(String userName) {         this.userName = userName;     }     public String getUserAddress() {         return userAddress;     }     public void setUserAddress(String userAddress) {         this.userAddress = userAddress;     }     public String getUserSex() {         return userSex;     }     public void setUserSex(String userSex) {         this.userSex = userSex;     }     public Date getUserBirthday() {         return userBirthday;     }     public void setUserBirthday(Date userBirthday) {         this.userBirthday = userBirthday;     }     @Override     public String toString() {         return "User{" +                 "userId=" + userId +                 ", userName='" + userName + '\'' +                 ", userAddress='" + userAddress + '\'' +                 ", userSex='" + userSex + '\'' +                 ", userBirthday=" + userBirthday +                 '}';     }     public static void main(String[] args) {         System.out.println("000");     } }

IAccountDao.java

package cn.itcast.dao; import cn.itcast.domin.Account; import java.util.List; public interface IAccountDao {     //查询所有账户信息，关联查询用户的信息。（一对一）     public List<Account> findAccount(); }

IUserDao.java

package cn.itcast.dao; import cn.itcast.domin.User; import java.util.List; public interface IUserDao {     //查询所有用户信息及用户关联的账户信息。（一对多）     public List<User> findUser(); }

IAccountDao.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="cn.itcast.dao.IAccountDao">     <resultMap id="accountMap" type="cn.itcast.domin.Account">         <!--Account类中的属性和account表中的列相对应         <id></id>：account表中主键的和Account类属性对象         -->         <!--注意column属性对应的是，sql语句查询出来的字段名（或者起的别名），不是表中的字段-->         <id property="aid" column="aid"></id>         <result property="uid" column="uid"></result>         <result property="money" column="money"></result>         <!--Account类中，引入User类         property:Account类中引入User类，所起的属性名（ private User user）         javaType：user的全类名         <id></id>：user表中主键的和User类属性对象         -->         <!--一对一-->         <association property="user" javaType="cn.itcast.domin.User">             <!--注意column属性对应的是，sql语句查询出来的字段名（或者起的别名），不是表中的字段-->             <id property="userId" column="id"></id>             <result property="userName" column="username"></result>             <result property="userBirthday" column="birthday"></result>             <result property="userSex" column="sex"></result>             <result property="userAddress" column="address"></result>         </association>     </resultMap>     <!--查询所有账户信息，关联查询用户的信息。(一个账户对应一个用户，一对一)-->     <select id="findAccount" resultMap="accountMap">         SELECT             a.*, u.*         FROM             account a,             USER u         WHERE             a.uid = u.id     </select> </mapper>

IUserDao.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="cn.itcast.dao.IUserDao">     <resultMap id="userMap" type="cn.itcast.domin.User">         <!--注意column属性对应的是，sql语句查询出来的字段名（或者起的别名），不是表中的字段-->         <id property="userId" column="id"></id>         <result property="userName" column="username"></result>         <result property="userBirthday" column="birthday"></result>         <result property="userSex" column="sex"></result>         <result property="userAddress" column="address"></result>         <!--User类中引入的List<Account> accounts             ofType:引入list的泛型         -->         <!--一对多 -->         <collection property="accounts" ofType="cn.itcast.domin.Account">             <!--注意column属性对应的是，sql语句查询出来的字段名（或者起的别名），不是表中的字段-->             <id property="aid" column="aid"></id>             <result property="uid" column="uid"></result>             <result property="money" column="money"></result>         </collection>     </resultMap>     <!--查询所有用户信息及用户关联的账户信息。（一对多）-->     <select id="findUser" resultMap="userMap">         SELECT           *         FROM           USER u         LEFT JOIN account a         ON a.`uid` = u.`id`     </select> </mapper>

多对多