【MyBatis】MyBatis基础教程(6)

前言：

本文内容：注解增删改查、Lombok使用、复杂查询环境搭建

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注解增删改查

我们可以在工具类创建的时候实现自动提交事务

MybatisUtil.java

// .......  
// 设置为true自动提交事务
public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession(true);
}

关于@Param()注解

• 基本类型的参数或者String类型，需要加
• 引用类型不需要加
• 如果只有一个基本类型的话，可以忽略(建议都加上)
• 在SQL中引用的就是@Param("value")里的value

#{},${}的区别：${}会存在SQL注入，而#{}不会

使用注解实现CRUD

UserMapper.java

// 使用注解实现CRUD
   // 查询 参数需要@Param("value") 以这个为主
   @Select("select * from user where id=#{id}")
   User getUserById(@Param("id") int id, @Param("name") String name);
   // 添加  引用对象不需要@Param 这里写实体类里的
   @Insert("insert into user(id,name,pwd) values(#{id},#{name},#{pwd})")
   int addUser(User user);
   // 修改
   @Update("update user set name=#{name},pwd=#{pwd} where id=#{id}")
   int updateUser(User user);
   // 删除
   @Delete("delete from user where id=#{id}")
   int deleteUser(@Param("id") int id);

MapperTest.java

// id查询
   @Test
   public void getUserById(){
       // 获得sqlSession对象
       SqlSession  sqlSession = MyBatisUtil.getSqlSession();
       // 执行sql
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       // mapper调用查询方法
       User user = mapper.getUserById(1,"admin");
       // 输出查询结果
           System.out.println(user);
       // 关闭sqlSession
       sqlSession.close();
   }
   // 添加
   @Test
   public void addUser(){
       // 获得sqlSession对象
       SqlSession  sqlSession = MyBatisUtil.getSqlSession();
       // 执行sql
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       // mapper调用添加方法
       mapper.addUser(new User(5, "小呆呆", "123123"));
       // 关闭sqlSession
       sqlSession.close();
   }
   // 修改
   @Test
   public void updateUser(){
       // 获得sqlSession对象
       SqlSession  sqlSession = MyBatisUtil.getSqlSession();
       // 执行sql
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       // mapper调用修改方法
       mapper.updateUser(new User(5, "小呆瓜", "33333"));
       // 关闭sqlSession
       sqlSession.close();
   }
   // 删除
   @Test
   public void deleteUser(){
       // 获得sqlSession对象
       SqlSession  sqlSession = MyBatisUtil.getSqlSession();
       // 执行sql
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       // mapper调用删除方法
       mapper.deleteUser(6);
       // 关闭sqlSession
       sqlSession.close();
   }

运行结果

===================ID查询=====================
Opening JDBC Connection
Created connection 592617454.
==>  Preparing: select * from user where id=?
==> Parameters: 1(Integer)
<==    Columns: id, name, pwd
<==        Row: 1, admin, 123
<==      Total: 1
User{id=1, name='admin', pwd='123'}
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@23529fee]
Returned connection 592617454 to pool.

Process finished with exit code 0

===================添加=====================
Opening JDBC Connection
Created connection 487075464.
==>  Preparing: insert into user(id,name,pwd) values(?,?,?)
==> Parameters: 5(Integer), 小呆呆(String), 123123(String)
<==    Updates: 1
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@1d082e88]
Returned connection 487075464 to pool.

Process finished with exit code 0
===================修改=====================
Opening JDBC Connection
Created connection 6320204.
==>  Preparing: update user set name=?,pwd=? where id=?
==> Parameters: 小呆瓜(String), 33333(String), 5(Integer)
<==    Updates: 1
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@60704c]
Returned connection 6320204 to pool.

Process finished with exit code 0 
===================删除=====================
Opening JDBC Connection
Created connection 112302969.
==>  Preparing: delete from user where id=?
==> Parameters: 6(Integer)
<==    Updates: 1
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@6b19b79]
Returned connection 112302969 to pool.

Process finished with exit code 0

Lombok的使用

官方简介

Project Lombok is a java library that automatically plugs into your editor and build tools, spicing up your java.
Never write another getter or equals method again, with one annotation your class has a fully featured builder, Automate your logging variables, and much more.

ProjectLombok是一个java库，可以自动插入到编辑器和构建工具中，提高java的性能。
永远不要再编写另一个getter或equals方法，使用一个注释，你的类就有了一个功能齐全的生成器，自动化了你的日志变量，等等。

官方地址：Project Lombok

通过下载安装lombok.jar或者引入Maven即可使用

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.24</version>
    <scope>provided</scope>
</dependency>

简单使用

通过IDEA安装Lombok插件(新版IDEA默认安装Lombok插件)

File->Settings-Plugins->搜索Lombok安装即可

在Pom.xml导入jar包

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.10</version>
    <scope>provided</scope>
</dependency>

如果导入异常，可以

File->Settings->Build, Execution, Deployment->Compiler->Annotation Processors->勾选Enable annotation processing

常用参数

@Getter and @Setter
@ToString
@EqualsAndHashCode
@AllArgsConstructor:有参构造@NoArgsConstructor:无参构造
@Data:无参构造，get,set,toString,hashCode,equals
@Accessors

pojo.java

package com.jokerdig.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;

import java.io.Serializable;

/**
 * 实体类
 * @author Joker大雄
 * @data 2022/4/23 - 15:22
 **/
// @Data可以帮我们实现get、set、toString、hashCode、无参构造
// @AllArgsConstructor 有参构造
@Data
@AllArgsConstructor
public class User implements Serializable {
    private int id;
    private String name;
    private String pwd;

}

优点及缺点

优点：

• 通过注解的形式自动生成构造器、getter/setter、equals、hashcode、toString等方法，提高了一定开发效率
• 让代码变得简洁，不用过多的去关注相应的方法
• 属性做修改时，也简化了维护为这些属性所生成的getter/setter方法等

缺点：

• 不支持多种参数构造器的重载
• 虽省去了手动创建getter/setter方法，但降低了源代码的可读性和完整性，阅读源码也不舒适

复杂查询环境搭建

一对多

• 对于老师而言，集合… 一个老师有很多学生

多对一

• 对于学生而言，关联… 多个学生，关联一个老师

搭建测试环境

创建老师和学生表

CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `teacher`(`id`, `name`) VALUES (1, '张三老师'); 

CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `fktid` (`tid`),
  CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher` (`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('1', '小明', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('2', '小红', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('3', '小张', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('4', '小李', '1'); 
INSERT INTO `student` (`id`, `name`, `tid`) VALUES ('5', '小王', '1');

父项目pom.xml添加

<!--        lombok-->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.10</version>
</dependency>

mybatis-config.xml

<?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">
<!--核心配置文件-->
<configuration>
    <!--    引入db.properties-->
    <!--  也可以在标签里传值，但优先使用外部配置-->
    <properties resource="db.properties"/>
<!--    配置日志工厂-->
    <settings>
<!--        标准日志工厂-->
        <setting name="logImpl" value="STDOUT_LOGGING"/>
<!--        log4j 不推荐使用-->
<!--        <setting name="logImpl" value="LOG4j"/>-->
    </settings>
    
    
<!--    配置别名 一-->
    <typeAliases>
        <typeAlias type="com.jokerdig.pojo.Teacher" alias="Teacher"/>
        <typeAlias type="com.jokerdig.pojo.Student" alias="Student"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
<!--    绑定接口-->
    <mappers>
        <mapper resource="com/jokerdig/mapper/TeacherMapper.xml"/>
        <mapper resource="com/jokerdig/mapper/StudentMapper.xml"/>
    </mappers>
</configuration>

项目结构

测试简单查询

Opening JDBC Connection
Created connection 597190999.
==>  Preparing: select * from teacher
==> Parameters: 
<==    Columns: id, name
<==        Row: 1, 张三老师
<==      Total: 1
Closing JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@23986957]
Returned connection 597190999 to pool.

Process finished with exit code 0