[Study]MyBatisPlus

Posted Spring-_-Bear

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一、入门案例

  1. 创建数据库与表

    CREATE DATABASE mybatis_plus;

USE mybatis_plus;

CREATE TABLE `user`  (
  `id` bigint NOT NULL AUTO_INCREMENT,
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,
  `age` int NULL DEFAULT NULL,
  `email` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 6 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_0900_ai_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES (1, '111', 111, '111@111.com');
INSERT INTO `user` VALUES (2, '222', 222, '222@222.com');
INSERT INTO `user` VALUES (3, '333', 333, '333@333.com');
INSERT INTO `user` VALUES (4, '444', 444, '444@444.com');
INSERT INTO `user` VALUES (5, '555', 555, '555@555.com');

  2. 创建 SpringBoot 工程，pom.xml 中引入依赖

    <!-- 引入 mysql connector、MyBatisPlus 依赖 -->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
</dependency>
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.5.1</version>
</dependency>

  3. 在 SpringBoot 工程的核心配置文件 application.yaml 中配置数据源信息

    spring:
  datasource:
    # 配置数据源类型
    type: com.zaxxer.hikari.HikariDataSource
    url: jdbc:mysql://localhost:3306/mybatis_plus?serverTimezone=GMT%2B8&characterEncoding=utf-8&useSSL=false
    driver-class-name: com.mysql.cj.jdbc.Driver
    username: admin
    password: admin

  4. 创建数据库表对应的实体类 User

    /**
 * 类名需要与数据库表名一致
 *
 * @author Spring-_-Bear
 * @datetime 2022-06-15 17:34
 */
@Data
public class User 
    private Long id;
    private String name;
    private Integer age;
    private String email;

  5. 创建 Mapper 接口 UserMapper

    /**
 * UserMapper.java
 * @author Spring-_-Bear
 * @datetime 2022-06-15 17:35
 */
public interface UserMapper extends BaseMapper<User>

  6. 创建 Service 接口及其实现类

    /**
 * UserService.java
 *
 * @author Spring-_-Bear
 * @datetime 2022-06-16 07:29
 */
@Service
public interface UserService extends IService<User> 


/**
 * UserServiceImpl.java
 * 
 * @author Spring-_-Bear
 * @datetime 2022-06-16 07:29
 */
@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User> implements UserService

  7. 在 SpringBoot 的配置类中开启接口所在包扫描

    @MapperScan("edu.whut.bear.mybatisplus.mapper")
@SpringBootApplication
public class MainApplication 
    public static void main(String[] args) 
        SpringApplication.run(MainApplication.class, args);

  8. application.yaml中加入日志功能

    mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

  9. 测试一把

    @SpringBootTest
class MainApplicationTests 
    @Autowired
    private UserMapper userMapper;

    @Test
    public void getAllUsers() 
        List<User> users = userMapper.selectList(null);
        users.forEach(System.out::println);

二、简单 CRUD

  1. 新增记录并返回自增主键

    @Test
public void insert() 
    User user = new User(null, "bear", 11, "bear@bear.com");
    int res = userMapper.insert(user);
    // User(id=1537210730757947393, name=bear, age=11, email=bear@bear.com)
    System.out.println(user);

  2. 通过指定条件删除记录、批量删除记录

    @Test
public void deleteByMap() 
    Map<String, Object> map = new HashMap<>();
    map.put("name", "bear");
    map.put("age", 13);
    // DELETE FROM user WHERE name = ? AND age = ?
    System.out.println(userMapper.deleteByMap(map));


@Test
public void deleteBatchIds() 
    List<Integer> list = Arrays.asList(1, 2, 3);
    // DELETE FROM user WHERE id IN ( ? , ? , ? )
    System.out.println(userMapper.deleteBatchIds(list));

  3. 通过实体类对象中的非空属性修改数据

    @Test
public void updateById() 
    User user = new User(4L, "springbear", 22, "2020@163.com");
    // UPDATE user SET name=?, age=?, email=? WHERE id=?
    System.out.println(userMapper.updateById(user));

  4. 不指定条件查询所有用户记录

    @Test
public void getAllUsers()
    List<User> users = userMapper.selectList(null);
    users.forEach(System.out::println);

三、常用注解

  1. @TableName 设置当前实体类对应的数据库表名

    /**
 * @author Spring-_-Bear
 * @datetime 2022-06-15 17:34
 */
@Data
@TableName("t_user")
public class User ...

  2. @TableId 将当前实体类的字段指定映射到数据库表的主键字段，value 属性指明数据库表主键名称，type 属性知名数据库表 id 自增类型

    public class User 
    /**
     * 将当前字段指定映射为数据库表的主键
     * 指定数据库表字段名，设置 ID 生成策略为自增 AUTO_INCREMENT
     */
    @TableId(value = "uid", type = IdType.AUTO)
    private Long id;

  3. @TableField 设置当前实体类对应的数据库表字段

    public class User
    /**
     * 设置 POJO 属性对应数据库表的字段名
     */
    @TableField("username")
    private String name;

  4. @TableLogic 设置当前字段逻辑删除字段，删除时逻辑删除对应的记录而非物理删除，查询时也总会带上记录存在的逻辑条件 ... WHERE isDELETED = 0 AND ...

    public class User
    /**
     * 设置为逻辑字段，当执行表记录删除操作时修改对应的 is_deleted 状态（默认为 0，修改后为 1）
     * 查询时总是查询 SELECT ... FROM ... WHERE id_deleted = 0，MyBatisPlus 中默认开启了自动驼峰命名转换
     */
    @TableLogic
    private Integer isDeleted;

四、Wrapper

4.1 继承体系图

4.2 QueryWrapper

  1. SELECT

    @Test
public void selectWrapper() 
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    // 查询 name 字段含有 bear 且年龄在 10-20 之间的记录
    queryWrapper.like("name", "bear").between("age", 10, 20);
    // SELECT id,name,age,email,is_deleted FROM t_user WHERE is_deleted=0 AND (name LIKE ? AND age BETWEEN ? AND ?)
    List<User> userList = userMapper.selectList(queryWrapper);
    userList.forEach(System.out::println);

  2. ORDER BY

    @Test
public void orderWrapper() 
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    // 先按 age 降序排，再按 id 升序排
    queryWrapper.orderByDesc("age").orderByAsc("id");
    // SELECT id,name,age,email,is_deleted FROM t_user WHERE is_deleted=0 ORDER BY age DESC,id ASC
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);

  3. DELETE

    @Test
public void deleteWrapper() 
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    // 删除 email 为空的记录
    queryWrapper.isNull("email");
    // DELETE FROM t_user WHERE (email IS NULL)
    int res = userMapper.delete(queryWrapper);
    System.out.println(res);

  4. UPDATE

    @Test
public void deleteWrapper() 
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    // 将【年龄大于 20 且名字中含有字母 a】或【邮箱为空】的用户信息进行修改
    queryWrapper.gt("age", 20).like("name", "a")
        .or().isNull("email");
    User user = new User(null, "springbear", 22, "springbear2020@163.com");
    // UPDATE t_user SET name=?, age=?, email=? WHERE (age > ? AND name LIKE ? OR email IS NULL)
    int res = userMapper.update(user, queryWrapper);
    System.out.println(res);

  5. 控制条件优先级

    @Test
public void priorityWrapper() 
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    // 将【名字中含有字母 a】并且【年龄大于 20 或邮箱为空的用户信息进行修改】，在 MyBatisPlus 中 Lambda 表达式中的条件会优先执行
    //  
    queryWrapper.like("name", "a")
        .and(i -> i.gt("age", 20).or().isNull("email"));
    User user = new User(null, "bear", 22, "bear@bear.com");
    // UPDATE t_user SET name=?, age=?, email=? WHERE (name LIKE ? AND (age > ? OR email IS NULL))
    int res = userMapper.update(user, queryWrapper);
    System.out.println(res);

  6. 查询特定的列

    @Test
public void columnWrapper() 
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    // 查询特定列
    queryWrapper.select("name", "age");
    // SELECT name,age FROM t_user
    List<Map<String, Object>> userMaps = userMapper.selectMaps(queryWrapper);
    userMaps.forEach(System.out::println);

  7. 子查询

    @Test
public void subQueryWrapper() 
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    // 子查询
    queryWrapper.inSql("id", "select id from t_user where id < 100");
    // SELECT id,name,age,email FROM t_user WHERE (id IN (select id from t_user where id < 100))
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);

  8. 条件组装查询（当满足指定的条件时才组装该条件）

    @Test
public void conditionWrapper() 
    String username = "springbear";
    int maxAge = 1000;
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    // 条件组装查询：username 中含有 "bear"，最大年龄小于 100
    queryWrapper.like(username.contains("bear"), "name", username)
        .lt(maxAge < 100, "age", maxAge);
    // SELECT id,name,age,email FROM t_user WHERE (name LIKE ?)
    List<User> users = userMapper.selectList(queryWrapper);
    users.forEach(System.out::println);

4.3 UpdateWrapper

@Test
public void updateWrapper() 
    UpdateWrapper<User> updateWrapper = new UpdateWrapper<>();
    // 将【名字中含有字母 a】并且【年龄大于 20 或邮箱为空的用户信息进行修改】，在 MyBatisPlus 中 Lambda 表达式中的条件会优先执行
    updateWrapper.like("name", "a")
        .and(i -> i.gt("age", 20).or().isNull("email"));
    // 设置要修改的字段
    updateWrapper.set("name", "熊猫");
    // UPDATE t_user SET name=? WHERE (name LIKE ? AND (age > ? OR email IS NULL))
    int res = userMapper.update(null, updateWrapper);
    System.out.println(res);

4.4 AbstractLambdaWrapper

@Test
public void lambdaQueryWrapper() 
    String name = "bear";
    int maxAge = 100;
    LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();
    // 使用 Lambda 函数式接口自动获取 POJO 字段对应的数据库表字段名（LambdaQueryWrapper 使用方法一致）
    lambdaQueryWrapper.like(name != null, User::getName, name)
        .ge(maxAge <= 100, User::getAge, maxAge);
    //  SELECT id,name,age,email FROM t_user WHERE (name LIKE ? AND age >= ?)
    List<User> users = userMapper.selectList(lambdaQueryWrapper);
    users.forEach(System.out::println);

五、高级功能

5.1 分页插件

  1. 在任意的配置类中配置分页组件 PaginationInnerInterceptor

    /**
 * 创建配置类配置 MyBatisPlus 分页组件
 *
 * @author Spring-_-Bear
 * @datetime 2022-06-16 16:59
 */
@Configuration
// 扫描 InterfaceMapper 所在包
@MapperScan("edu.whut.bear.mybatisplus.mapper")
public class MyBatisPlusConfig 
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() 
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        // 设置数据库的类型
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;

  2. 测试一把

    @Test
public void page() 
    int currentPage = 1<
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