mybatis 一对一，一对多，多对多关系映射查询操作

Posted 2021-03-03 zsbenn

 定义两个类（对应数据库内两张表） User ,Account，每个Account属于一个User

User类 及其 对应的IUserDao

package com.itheima.domain;

import java.io.Serializable;
import java.util.Date;
import java.util.List;

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    //一对多关系映射，主表实体应该包含从表实体的集合引用
    private List<Account> accounts;

    public List<Account> getAccounts() {
        return accounts;
    }

    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username=‘" + username + ‘‘‘ +
                ", birthday=" + birthday +
                ", sex=‘" + sex + ‘‘‘ +
                ", address=‘" + address + ‘‘‘ +
                ‘}‘;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }
}

View Code

package com.itheima.dao;

import com.itheima.domain.QueryVo;
import com.itheima.domain.User;

import java.util.List;

public interface IUserDao {
    /*
    * 查询所有操作
    * */
    List<User> findAll();

    /*
    * 保存一条记录并返回id（直接将id赋给对应的属性）
    * */
    void saveUser(User user);

    /*
    * 更新用户
    * */
    void updateUser(User user);

    /*
    * 删除用户
    * */
    void deleteUser(Integer userId);

    /*
    * 根据Id查询User
    * */
    User findById(Integer userId);

    /*
    * 模糊查询
    * */
    List<User> findByName(String username);

    /*
    * 查询User总数
    * */
    int findTotal();

    /*
    *  根据queryVo查询中的条件查询用户
    * */
    List<User> findByVo(QueryVo vo);

    /*
    * 根据传入参数条件查询
    * @param user 查询的条件：有可能有用户名，有可能有性别，也有可能有地址，可能啥都没有
    * */
    List<User> findUserByCondition(User user);

    /*
    * 根据queryVo中提供的id集合查询用户信息
    * */
    List<User> findUserInIds(QueryVo vo);
}

View Code

Account类 及其对应的 IAccountDao

package com.itheima.domain;

import java.io.Serializable;

public class Account implements Serializable {
    private Integer id;
    private Integer uid;
    private Double money;

    //从表实体应该包含一个主表实体的对像引用
    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.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;
    }

    @Override
    public String toString() {
        return "Account{" +
                "id=" + id +
                ", uid=" + uid +
                ", money=" + money +
                ‘}‘;
    }
}

View Code

package com.itheima.dao;

import com.itheima.domain.Account;
import com.itheima.domain.AccountUser;

import java.util.List;

public interface IAccountDao {

    /*
    * 查询所有Account
    * */
    List<Account> findAll();

    /*
    * 查询所有账户，并且带有用户名和地址
    * */
    List<AccountUser> findAllAccountUser();

}

View Code

 

一对一(多对一)的关系查询：查询Account时也要查询出所属User的信息

显然每个Account对应了一个User

//从表实体应该包含一个主表实体的对像引用
    private User user;

下面是IAccountDao.xml 对于 findAll方法的配置

<?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.itheima.dao.IAccountDao">

    <!--定义封装account和user的resultMap-->
    <resultMap id="accountUserMap" type="com.itheima.domain.Account">
        <id property="id" column="aid"></id>
        <result property="uid" column="uid"></result>
        <result property="money" column="money"></result>
        <!--一对一关系映射，配置封装user的内容，column：外键，javaType:联系对象的全限定类名-->
        <association property="user" column="uid" javaType="com.itheima.domain.User">
            <id property="id" column="id"></id>
            <result column="username" property="username"></result>
            <result column="address" property="address"></result>
            <result column="sex" property="sex"></result>
            <result column="birthday" property="birthday"></result>
        </association>
    </resultMap>

    <!--查询所有Account并获得对应User信息(多对一标准写法)-->
    <select id="findAll" resultMap="accountUserMap">
        select u.*, a.id as aid, a.uid, a.money
        from account as a, user as u
        where u.id = a.uid
    </select>

    <!--查询所有Account，同时包含用户名和地址信息-->
    <select id="findAllAccountUser" resultType="com.itheima.domain.AccountUser">
        select a.*,u.username,u.address from account as a, user as u
        where a.uid = u.id;
    </select>
    
</mapper>

测试代码

/*
    * 查询所有Account并获得对应User信息(多对一标准写法)
    * */
    @Test
    public void testFindAll(){
        List<Account> accounts = accountDao.findAll();
        for(Account account:accounts)
            System.out.println(account+account.getUser().toString());
    }

 

一对多的关系查询：查询User时查询所有和其相关的Account集合

类似Account类内声明一个User的引用，User内也声明了一个Account类的集合

//一对多关系映射，主表实体应该包含从表实体的集合引用
    private List<Account> accounts;

IUserDao.xml 关于 findAll方法的配置

<resultMap id="userAccountMap" type="com.itheima.domain.User">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="address" column="address"></result>
        <result property="sex" column="sex"></result>
        <result property="birthday" column="birthday"></result>
        <!--配置user对象中accounts集合的映射,ofTpe:集合中元素的全限定类名-->
        <collection property="accounts" ofType="com.itheima.domain.Account">
            <id property="id" column="aid"></id>
            <result property="uid" column="uid"></result>
            <result property="money" column="money"></result>
        </collection>

    </resultMap>

    <!--配置查询所有-->
    <select id="findAll" resultMap="userAccountMap">
        select * from user as u left outer join account as a
        on u.id = a.uid
    </select>

测试方法

@Test
    public void testFindAll()throws Exception{
        //5.使用代理对象执行方法
        List<User>users = userDao.findAll();
        for(User user:users) {
            System.out.println("---------每个用户的信息----------");
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }