Mybatis笔记3

淩亂°似流年 2021-12-03 02:29 218阅读 0赞

**Mybatis映射文件的SQL深入**

(Mybatis今天学的不多，看了半天的mysql必知必会)

动态sql语句-if语句，查询一个用户的时候，有可能根据地址查询，用户名查询，性别查询等，所以需要动态sql语句

1.接口中新添加方法

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，还有可能是都有 List<User> findUserByCondition(User user);

2.配置文件的写法，根据条件查询

<select id="findUserByCondition" resultType="userMap" parameterType="user"> select * from user where 1=1 <if test="userName != null"> and username=#{userName} </if> </select>

3.测试方法

public void testFindByCondition(){ User u = new User(); u.setUserName("老王"); //5.执行查询所有方法 List<User> users = userDao.findUserByCondition(u); for(User user : users){ System.out.println(user); } }

**mybatis中的多表查询**

示例：用户和账户，一个用户可以有多个账户，一个账户只能属于一个用户

步骤：

1.  建立两张表：用户表和账户表，让用户表和账户表之间具备一对多的关系：需要使用外键在账户表中添加
2.  建立两个实体类：用户实体类和账户实体类，让用户和账户的实体类能体现出一对多的关系
3.  建立两个配置文件，用户的配置文件和账户的配置文件
4.  实现配置：当我们查询用户是，可以同时得到用户下所包含的账户信息，当我们查询账户是，可以同时得到账户的所属用户信息

账户表的创建

![img][]

用户表的创建

![img][img 1]

接口的建立

用户接口

public interface IAccountDao { //查询所有账户 List<Account> finaAll(); }

账户接口

public interface IUserDao { /** * 查询所有用户 */ List<User> findAll(); /** * 根据id查询用户信息 */ User findById(Integer userId); }

**用户实体类的建立**

用户实体类

package com.itheima.domain; import java.io.Serializable; import java.util.Date; public class User implements Serializable { private Integer id; private String username; private String address; private String sex; private Date birthday; @Override public String toString() { return "User{" + "id=" + id + ", username='" + username + '\'' + ", address='" + address + '\'' + ", sex='" + sex + '\'' + ", birthday=" + birthday + '}'; } 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 String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } }

账户实体类

package com.itheima.domain; import java.io.Serializable; public class Account implements Serializable { private Integer id; private Integer uid; private Double money; @Override public String toString() { return "Account{" + "id=" + id + ", uid=" + uid + ", money=" + money + '}'; } 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; } }

**初步的配置文件**

用户的

<?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.IUserDao">
    
        
        <select id="findAll" resultType="user">
           select * from user
        </select>
    
        
        <select id="findById" parameterType="INT" resultType="user">
            select * from user where id = #{uid}
        </select>
    </mapper>

账户的

目的：查询所有账户，同时还有获取到当前账户的所属用户信息

![img][img 2]

添加一个实体类，继承Account

package com.itheima.domain; //让他继承Account public class AccountUser extends Account{ //只需要用户名和地址 private String username; private String address; public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } @Override public String toString() { //让他先调用父类的toString return super.toString()+" AccountUser{" + "username='" + username + '\'' + ", address='" + address + '\'' + '}'; } }

接口添加方法

//查询所有账户，并且带有用户名称和地址名称 List<AccountUser> findAllAccount();

test类实现功能

@Test //查询所有账户，同时包含用户名称和地址 public void testFindAllAccountUser(){ List<AccountUser> aus = accountDao.findAllAccount(); for(AccountUser au :aus){ System.out.println(au); } }

![img][img 3]

![img][img 4]

![img][img 5]

转载于:https://www.cnblogs.com/train99999/p/11192373.html

[img]: https://www.z4a.net/images/2019/07/15/imagecedc33d845da229d.png
[img 1]: https://www.z4a.net/images/2019/07/15/imageed3eec88029669a7.png
[img 2]: https://www.z4a.net/images/2019/07/15/image509167042db7b855.png
[img 3]: https://www.z4a.net/images/2019/07/15/image62e03a1dc9dc5d7e.png
[img 4]: https://www.z4a.net/images/2019/07/15/image7853ef12b1d36f79.png
[img 5]: https://www.z4a.net/images/2019/07/15/image46a556a2d9a4d888.png