使用MyBatis-Plus 操作数据库CRUD_mybatis-plus执行insert操作的时候,对象中的createuser=null,但是执行

1、配置pom.xml

  <!--mybatis-plus 的SpringBoot的启动配置文件-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.3.2</version>
        </dependency>
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2、文件配置application.yml

#    配置mybatis-plus
mybatis-plus:
  configuration:
    #    打印sql语句
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  #配置枚举映射类
  type-enums-package:
    com.springboot.mybatisplus.enums
  #  配置逻辑删除（假删除） 注解 @TableLogic
  global-config:
    db-config:
      logic-delete-value: 1
      logic-not-delete-value: 0
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3、注解详解

@TableName

映射数据库的表名

@Data
@TableName(value = "user")
public class Account {
    private Integer id;
    private String name;
    private Integer age;
}
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@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);
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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

@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;
}
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3、创建自动填充处理器

@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);
    }
}
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@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

@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;
}
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3、注册配置类

@Configuration
public class MyBatisPlusConfig {
    
    @Bean
    public OptimisticLockerInterceptor optimisticLockerInterceptor(){
        return new OptimisticLockerInterceptor();
    }
    
}
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@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

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;
}
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@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;
}
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application.yml

type-enums-package: 
  com.southwind.mybatisplus.enums
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2、实现接口

public enum AgeEnum implements IEnum<Integer> {
    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;
    }
}
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@TableLogic

映射逻辑删除

1、数据表添加 deleted 字段

2、实体类添加注解

@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;
}
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3、application.yml 添加配置

global-config:
  db-config:
    logic-not-delete-value: 0
    logic-delete-value: 1
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查询

//mapper.selectList(null);
QueryWrapper wrapper = new QueryWrapper();
//        Map<String,Object> 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);
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//        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<String,Object> 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<User> page = new Page<>(2,2);
//        Page<User> result = mapper.selectPage(page,null);
//        System.out.println(result.getSize());
//        System.out.println(result.getTotal());
//        result.getRecords().forEach(System.out::println);

//        Page<Map<String,Object>> 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));
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自定义 SQL（多表关联查询）

@Data
public class ProductVO {
    private Integer category;
    private Integer count;
    private String description;
    private Integer userId;
    private String userName;
}
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public interface UserMapper extends BaseMapper<User> {
    @Select("select p.*,u.name userName from product p,user u where p.user_id = u.id and u.id = #{id}")
    List<ProductVO> productList(Integer id);
}
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添加

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

//mapper.deleteById(1);
//        mapper.deleteBatchIds(Arrays.asList(7,8));
//        QueryWrapper wrapper = new QueryWrapper();
//        wrapper.eq("age",14);
//        mapper.delete(wrapper);

Map<String,Object> map = new HashMap<>();
map.put("id",10);
mapper.deleteByMap(map);
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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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视频地址