【Java】MyBatis Plus入门

正文索引 [隐藏]

MyBatis plus快速上手

1. 创建Maven工程
Spring Boot(2.3.0) + MyBatis Plus(国产的开源框架,并没有接入到 Spring 官方孵化器中)
2. 在pom.xml导入依赖

<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>3.3.1.tmp</version>
</dependency>

3. 新建实体类
package com.southwind.mybatisplus.entity;
import lombok.Data;
@Data
public class User {
private Integer id;
private String name;
private Integer age;
}

4. 创建Mapper接口
package com.southwind.mybatisplus.mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.southwind.mybatisplus.entity.User;
public interface UserMapper extends BaseMapper {
}

5. application.yml
spring:
datasource:
driver-class-name: com.mysql.cj.jdbc.Driver
url: jdbc:mysql://localhost:3306/db?useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8
username: root
password: root
mybatis-plus:
configuration:
log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

6. 启动类需要扫描Mapper包
package com.southwind.mybatisplus;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
@MapperScan("com.southwind.mybatisplus.mapper")
public class MybatisplusApplication {
public static void main(String[] args) {
SpringApplication.run(MybatisplusApplication.class, args);
}
}

7. 测试
package com.southwind.mybatisplus.mapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
@SpringBootTest
class UserMapperTest {
@Autowired
private UserMapper mapper;
@Test
void test(){
mapper.selectList(null).forEach(System.out::println);
}
}

常用注解

  • @TableName
  • 映射数据库的表名

    package com.southwind.mybatisplus.entity;
    import com.baomidou.mybatisplus.annotation.TableName;
    import lombok.Data;
    @Data
    @TableName(value = "user")
    public class Account {
    private Integer id;
    private String name;
    private Integer age;
    }

  • @TableId
  • 设置主键映射,value 映射主键字段名
    type 设置主键类型,主键的生成策略,

    AUTO(0),
    NONE(1),
    INPUT(2),
    ASSIGN_ID(3),
    ASSIGN_UUID(4),
    /** @deprecated */
    @Deprecated
    ID_WORKER(3),
    /** @deprecated */
    @Deprecated
    ID_WORKER_STR(3),
    /** @deprecated */
    @Deprecated
    UUID(4);

    INPUT 如果开发者没有手动赋值,则数据库通过自增的方式给主键赋值,如果开发者手动赋值,则存入该值。
    AUTO 默认就是数据库自增,开发者无需赋值。
    ASSIGN_ID MP 自动赋值,雪花算法。
    ASSIGN_UUID 主键的数据类型必须是 String,自动生成 UUID 进行赋值

  • @TableField
  • 映射非主键字段,value 映射字段名
    exist 表示是否为数据库字段 false,如果实体类中的成员变量在数据库中没有对应的字段,则可以使用 exist,VO、DTO
    select 表示是否查询该字段
    fill 表示是否自动填充,将对象存入数据库的时候,由 MyBatis Plus 自动给某些字段赋值,create_time、update_time
    1、给表添加 create_time、update_time 字段
    2、实体类中添加成员变量

    package com.southwind.mybatisplus.entity;
    import com.baomidou.mybatisplus.annotation.FieldFill;
    import com.baomidou.mybatisplus.annotation.TableField;
    import com.baomidou.mybatisplus.annotation.TableId;
    import com.baomidou.mybatisplus.annotation.TableName;
    import lombok.Data;
    import java.util.Date;
    @Data
    @TableName(value = "user")
    public class User {
    @TableId
    private String id;
    @TableField(value = "name",select = false)
    private String title;
    private Integer age;
    @TableField(exist = false)
    private String gender;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
    }

    3. 创建自动填充处理器
    package com.southwind.mybatisplus.handler;
    import com.baomidou.mybatisplus.core.handlers.MetaObjectHandler;
    import org.apache.ibatis.reflection.MetaObject;
    import org.springframework.stereotype.Component;
    import java.util.Date;
    @Component
    public class MyMetaObjectHandler implements MetaObjectHandler {
    @Override
    public void insertFill(MetaObject metaObject) {
    this.setFieldValByName("createTime",new Date(),metaObject);
    this.setFieldValByName("updateTime",new Date(),metaObject);
    }
    @Override
    public void updateFill(MetaObject metaObject) {
    this.setFieldValByName("updateTime",new Date(),metaObject);
    }
    }

  • @Version
  • 标记乐观锁,通过 version 字段来保证数据的安全性,当修改数据的时候,会以 version 作为条件,当条件成立的时候才会修改成功。
    version = 2
    线程 1:update ... set version = 2 where version = 1
    线程2 :update ... set version = 2 where version = 1
    1、数据库表添加 version 字段,默认值为 1
    2、实体类添加 version 成员变量,并且添加 @Version

    package com.southwind.mybatisplus.entity;
    import com.baomidou.mybatisplus.annotation.*;
    import lombok.Data;
    import java.util.Date;
    @Data
    @TableName(value = "user")
    public class User {
    @TableId
    private String id;
    @TableField(value = "name",select = false)
    private String title;
    private Integer age;
    @TableField(exist = false)
    private String gender;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
    @Version
    private Integer version;
    }

    3. 注册配置类
    package com.southwind.mybatisplus.config;
    import com.baomidou.mybatisplus.extension.plugins.OptimisticLockerInterceptor;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.annotation.Configuration;
    @Configuration
    public class MyBatisPlusConfig {
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor(){
    return new OptimisticLockerInterceptor();
    }
    }

  • @EnumValue
  • 1. 通用枚举类注解,将数据库字段映射成实体类的枚举类型成员变量

    package com.southwind.mybatisplus.enums;
    import com.baomidou.mybatisplus.annotation.EnumValue;
    public enum StatusEnum {
    WORK(1,"上班"),
    REST(0,"休息");
    StatusEnum(Integer code, String msg) {
    this.code = code;
    this.msg = msg;
    }
    @EnumValue
    private Integer code;
    private String msg;
    }

    package com.southwind.mybatisplus.entity;
    import com.baomidou.mybatisplus.annotation.*;
    import com.southwind.mybatisplus.enums.StatusEnum;
    import lombok.Data;
    import java.util.Date;
    @Data
    @TableName(value = "user")
    public class User {
    @TableId
    private String id;
    @TableField(value = "name",select = false)
    private String title;
    private Integer age;
    @TableField(exist = false)
    private String gender;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
    @Version
    private Integer version;
    private StatusEnum status;
    }

    application.yml
    type-enums-package:
    com.southwind.mybatisplus.enums

    2. 实现接口
    package com.southwind.mybatisplus.enums;
    import com.baomidou.mybatisplus.core.enums.IEnum;
    public enum AgeEnum implements IEnum {
    ONE(1,"一岁"),
    TWO(2,"两岁"),
    THREE(3,"三岁");
    private Integer code;
    private String msg;
    AgeEnum(Integer code, String msg) {
    this.code = code;
    this.msg = msg;
    }
    @Override
    public Integer getValue() {
    return this.code;
    }
    }

  • @TableLogic
  • 映射逻辑删除

    1、数据表添加 deleted 字段

    2、实体类添加注解

    package com.southwind.mybatisplus.entity;
    import com.baomidou.mybatisplus.annotation.*;
    import com.southwind.mybatisplus.enums.AgeEnum;
    import com.southwind.mybatisplus.enums.StatusEnum;
    import lombok.Data;
    import java.util.Date;
    @Data
    @TableName(value = "user")
    public class User {
    @TableId
    private String id;
    @TableField(value = "name",select = false)
    private String title;
    private AgeEnum age;
    @TableField(exist = false)
    private String gender;
    @TableField(fill = FieldFill.INSERT)
    private Date createTime;
    @TableField(fill = FieldFill.INSERT_UPDATE)
    private Date updateTime;
    @Version
    private Integer version;
    @TableField(value = "status")
    private StatusEnum statusEnum;
    @TableLogic
    private Integer deleted;
    }

    3、application.yml 添加配置
    global-config:
    db-config:
    logic-not-delete-value: 0
    logic-delete-value: 1

查询

//mapper.selectList(null);
QueryWrapper wrapper = new QueryWrapper();
// Map map = new HashMap<>();
// map.put("name","小红");
// map.put("age",3);
// wrapper.allEq(map);
// wrapper.gt("age",2);
// wrapper.ne("name","小红");
// wrapper.ge("age",2);
//like '%小'
// wrapper.likeLeft("name","小");
//like '小%'
// wrapper.likeRight("name","小");
//inSQL
// wrapper.inSql("id","select id from user where id < 10"); // wrapper.inSql("age","select age from user where age > 3");
// wrapper.orderByDesc("age");
// wrapper.orderByAsc("age");
// wrapper.having("id > 8");
mapper.selectList(wrapper).forEach(System.out::println);

//        System.out.println(mapper.selectById(7));
// mapper.selectBatchIds(Arrays.asList(7,8,9)).forEach(System.out::println);
//Map 只能做等值判断,逻辑判断需要使用 Wrapper 来处理
// Map map = new HashMap<>();
// map.put("id",7);
// mapper.selectByMap(map).forEach(System.out::println);
QueryWrapper wrapper = new QueryWrapper();
wrapper.eq("id",7);
//// System.out.println(mapper.selectCount(wrapper));
//
// //将查询的结果集封装到Map中
// mapper.selectMaps(wrapper).forEach(System.out::println);
// System.out.println("-------------------");
// mapper.selectList(wrapper).forEach(System.out::println);
//分页查询
// Page page = new Page<>(2,2);
// Page result = mapper.selectPage(page,null);
// System.out.println(result.getSize());
// System.out.println(result.getTotal());
// result.getRecords().forEach(System.out::println);
// Page> page = new Page<>(1,2);
// mapper.selectMapsPage(page,null).getRecords().forEach(System.out::println);
// mapper.selectObjs(null).forEach(System.out::println);
System.out.println(mapper.selectOne(wrapper));

自定义 SQL(多表关联查询)

package com.southwind.mybatisplus.entity;
import lombok.Data;
@Data
public class ProductVO {
private Integer category;
private Integer count;
private String description;
private Integer userId;
private String userName;
}

package com.southwind.mybatisplus.mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.southwind.mybatisplus.entity.ProductVO;
import com.southwind.mybatisplus.entity.User;
import org.apache.ibatis.annotations.Select;
import java.util.List;
public interface UserMapper extends BaseMapper {
@Select("select p.*,u.name userName from product p,user u where p.user_id = u.id and u.id = #{id}")
List productList(Integer id);
}

添加

User user = new User();
user.setTitle("小明");
user.setAge(22);
mapper.insert(user);
System.out.println(user);

删除

//mapper.deleteById(1);
// mapper.deleteBatchIds(Arrays.asList(7,8));
// QueryWrapper wrapper = new QueryWrapper();
// wrapper.eq("age",14);
// mapper.delete(wrapper);
Map map = new HashMap<>();
map.put("id",10);
mapper.deleteByMap(map);

修改

//        //update ... version = 3 where version = 2
// User user = mapper.selectById(7);
// user.setTitle("一号");
//
// //update ... version = 3 where version = 2
// User user1 = mapper.selectById(7);
// user1.setTitle("二号");
//
// mapper.updateById(user1);
// mapper.updateById(user);
User user = mapper.selectById(1);
user.setTitle("小红");
QueryWrapper wrapper = new QueryWrapper();
wrapper.eq("age",22);
mapper.update(user,wrapper);
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