MybatisPlus学习笔记

1.创建数据库，创建数据库表

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user`  (
  `id` bigint NOT NULL COMMENT '编号',
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '姓名',
  `age` int NULL DEFAULT NULL COMMENT '年龄',
  `email` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL COMMENT '邮箱',
  `create_time` datetime NULL DEFAULT NULL COMMENT '创建时间',
  `update_time` datetime NULL DEFAULT NULL COMMENT '更新时间',
  `version` int NULL DEFAULT NULL COMMENT '版本号',
  `deleted` int NULL DEFAULT NULL COMMENT '是否删除',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES (1, '小小', 18, 'xiaohong@email.com', NULL, NULL, NULL, 0);
INSERT INTO `user` VALUES (2, '小白', 20, 'xiaobai@email.com', NULL, NULL, NULL, 0);
INSERT INTO `user` VALUES (3, '小黑', 28, 'xiaohei@email.com', NULL, NULL, NULL, 0);
INSERT INTO `user` VALUES (4, '小绿', 21, 'xiaolv@email.com', NULL, NULL, NULL, 0);
INSERT INTO `user` VALUES (5, '小紫', 24, 'xiaozi@email.com', NULL, NULL, NULL, 0);
INSERT INTO `user` VALUES (1443101546259562498, '小橙', 20, 'xiaocheng@email.com', NULL, NULL, NULL, 1);
INSERT INTO `user` VALUES (1443113324154621953, '小青', 20, 'xiaocheng@email.com', '2021-09-29 15:20:03', '2021-09-29 15:20:53', NULL, 0);
INSERT INTO `user` VALUES (1443461637085245441, '张三', 20, 'lisi@email.com', '2021-09-30 14:24:07', '2021-09-30 14:45:52', 2, 1);
INSERT INTO `user` VALUES (1443479768882565121, '王五', 20, 'lisi@email.com', '2021-09-30 15:36:10', '2021-09-30 15:36:10', 1, 1);

SET FOREIGN_KEY_CHECKS = 1;

2.创建spring boot demo

3.引入相关依赖

<!--MybatisPlus-->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.3.1</version>
</dependency>
<!--MySQL-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.25</version>
</dependency>
<!--lombok-->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <optional>true</optional>
</dependency>

4.编写配置文件

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/mp?serverTimezone=GMT%2B8
spring.datasource.username=root
spring.datasource.password=root

5.编写代码

5.1 创建entity包编写实体类：User.java

@Data
public class User {
    private Long id;
    private String name;
    private Integer age;
    private String email;
}

5.2 创建mapper包编写Mapper接口：UserMapper.java

public interface UserMapper extends BaseMapper<User> {
}

5.3 在入口类加入注解

@SpringBootApplication
@MapperScan("com.zhi.mapper")
public class MpDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(MpDemoApplication.class, args);
    }
}

5.4 配置 mybatis 日志

#mybatis日志
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

5.5 测试

@SpringBootTest
class MpDemoApplicationTests {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void update(){
        User user = new User();
        user.setId(1L);
        user.setName("小小");
        int i = userMapper.updateById(user);
        System.out.println(i);
    }

    @Test
    public void findAll() {
        List<User> users = userMapper.selectList(null);
        System.out.println(users);
    }

    @Test
    public void insert(){
        User user = new User();
        user.setName("小橙");
        user.setAge(20);
        user.setEmail("xiaocheng@email.com");
        int insert = userMapper.insert(user);
        System.out.println(insert);
    }
}

5.6 查看sql日志

==>  Preparing: SELECT id,name,age,email FROM user
==> Parameters: 
<==    Columns: id, name, age, email
<==        Row: 1, 小红, 18, xiaohong@email.com
<==        Row: 2, 小白, 20, xiaobai@email.com
<==        Row: 3, 小黑, 28, xiaohei@email.com
<==        Row: 4, 小绿, 21, xiaolv@email.com
<==        Row: 5, 小紫, 24, xiaozi@email.com
<==        Row: 1443101546259562498, 小橙, 20, xiaocheng@email.com
<==      Total: 6

6.主键策略 MybatisPlus的默认的主键策略是：ASSIGN_ID(雪花算法)

@TableId(type = IdType.ASSIGN_ID)
private Long id;

要想影响所有实体的配置，可以设置全局主键配置

#全局设置主键生成策略
mybatis-plus.global-config.db-config.id-type=assign_id

7.自动填充

7.1 准备工作 添加 datetime 类型的新字段 create_time,update_time

在表对应实体类添加对应属性

7.2 在实体类要进行自动填充属性添加注解

@TableField(fill = FieldFill.INSERT)
private Date createTime;    //create_time
@TableField(fill = FieldFill.INSERT_UPDATE)
private Date updateTime;    //update_time

7.3 创建MyMetaObjectHandler类

@Component      //把这个类的对象交给spring管理
public class MyMetaObjectHandler implements MetaObjectHandler {

    //mp执行添加操作时这个方法执行
    @Override
    public void insertFill(MetaObject metaObject) {
        //根据名称设置属性值
        this.setFieldValByName("createTime",new Date(),metaObject);
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }

    //mp执行更新操作时这个方法执行
    @Override
    public void updateFill(MetaObject metaObject) {
        this.setFieldValByName("updateTime",new Date(),metaObject);
    }
}

8.乐观锁实现流程 乐观锁是用于解决问题的一种方式

8.1修改实体类 在表添加字段作为版本号，在表对应实体类添加版本号属性

在实体类进行版本号操作的属性上面添加 @Version 注解

@Version
private Integer version;

8.2注册乐观锁插件 把 @MapperScan 注解从入口类转移到 MpConfig 中并注册乐观锁

@Configuration
@MapperScan("com.zhi.mapper")
public class MpConfig {
    /*
    乐观锁插件
     */
    @Bean
    public OptimisticLockerInnerInterceptor optimisticLockerInnerInterceptor(){
        return new OptimisticLockerInnerInterceptor();
    }
}

9查询

9.1多个id批量查询

//多个id批量查询
@Test
public void testSelect1(){
    List<User> users = userMapper.selectBatchIds(Arrays.asList(1, 2, 3));
    System.out.println(users);
}

9.2简单条件查询

//简单条件查询
@Test
public void testSelect2(){
    HashMap<String, Object> columnMap = new HashMap<>();
    columnMap.put("name","张三");
    columnMap.put("age",20);
    List<User> users = userMapper.selectByMap(columnMap);
    System.out.println(users);
}

10分页查询

10.1在MpConfig中配置分页插件

@Bean
public PaginationInterceptor paginationInterceptor(){
    return new PaginationInterceptor();
}

10.2编写分页代码

(1)插入Page对象，传入俩个参数分别为当前页和每页记录数
(2)调用mp的方法实现分页

//分页查询
@Test
public void testSelectPage(){
    //第一个为当前页，第二个为每页显示几个
    Page<User> page = new Page<>(1,3);
    Page<User> userPage = userMapper.selectPage(page, null);
    long pages = userPage.getPages();           //获取总页数
    long current = userPage.getCurrent();       //当前页
    List<User> records = userPage.getRecords(); //当前数据的集合
    long total = userPage.getTotal();           //表中总记录数
    boolean b = userPage.hasNext();             //是否有下一页
    boolean b1 = userPage.hasPrevious();        //是否有上一页
    System.out.println(userPage);
}

11删除与逻辑删除

11.1删除

//根据id删除
@Test
public void testDeleteId(){
    int i = userMapper.deleteById(1L);
    System.out.println(i);
}
//根据条件删除
@Test
public void testDeleteByMap(){
    HashMap<String, Object> objectObjectHashMap = new HashMap<>();
    objectObjectHashMap.put("name","小黑");
    objectObjectHashMap.put("age",28);
    int i = userMapper.deleteByMap(objectObjectHashMap);
    System.out.println(i);
}
//批量删除
@Test
public void testDeleteBeachIds(){
    int i = userMapper.deleteBatchIds(Arrays.asList(2, 3));
    System.out.println(i);
}

11.2逻辑删除

(1)在表中添加字段，对应实体类添加属性，作为逻辑删除标志

private Integer deleted;

(2)在实体类逻辑删除的属性上添加注解

@TableLogic
@TableField(fill = FieldFill.INSERT)
private Integer deleted;

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