MyBaits-Plus

Annotations

Annotations

MyBatis-Plus infers table information based on the PO (Persistent Object) entity details to generate SQL. By default:

• MyBatis-Plus converts the PO entity class name from camelCase to snake_case for the table name.
• MyBatis-Plus converts all variable names in the PO entity from camelCase to snake_case for the column names, and infers the column types from the variable types.
• MyBatis-Plus treats a field named id as the primary key. However, the default implementation often does not match actual scenarios, so MyBatis-Plus provides several annotations to facilitate the declaration of table information. Annotations: https://baomidou.com/reference/annotation/ Key annotations: @TableName, @TableId, @TableField

Configuration

mybatis-plus:
  type-aliases-package: com.xxx.mp.domain.po
  global-config:
    db-config:
      id-type: auto # id auto-increment

https://baomidou.com/reference/

Wrapper and LambdaWrapper

QueryWrapper和UpdateWrapper

@Test
void testQueryWrapper() {
    // 1.构建查询条件 where name like "%o%" AND balance >= 1000
    QueryWrapper<User> wrapper = new QueryWrapper<User>()
            .select("id", "username", "info", "balance")
            .like("username", "o")
            .ge("balance", 1000);
    // 2.查询数据
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

@Test
void testUpdateWrapper() {
    List<Long> ids = List.of(1L, 2L, 4L);
    // 1.生成SQL
    UpdateWrapper<User> wrapper = new UpdateWrapper<User>()
            .setSql("balance = balance - 200") // SET balance = balance - 200
            .in("id", ids); // WHERE id in (1, 2, 4)
        // 2.更新，注意第一个参数可以给null，也就是不填更新字段和数据，
    // 而是基于UpdateWrapper中的setSQL来更新
    userMapper.update(null, wrapper);
}

To avoid String Hard Code above, we can use LambdaWrapper

e.g.

@Test
void testLambdaQueryWrapper() {
    // 1.构建条件 WHERE username LIKE "%o%" AND balance >= 1000
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.lambda()
            .select(User::getId, User::getUsername, User::getInfo, User::getBalance)
            .like(User::getUsername, "o")
            .ge(User::getBalance, 1000);
    // 2.查询
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

DIY SQL

We can use Wrapper to generate the condition expression (the condition after WHERE clause), and combine it with mapper.xml

@Test
void testCustomWrapper() {
    // 1.准备自定义查询条件
    List<Long> ids = List.of(1L, 2L, 4L);
    QueryWrapper<User> wrapper = new QueryWrapper<User>().in("id", ids);

    // 2.调用mapper的自定义方法，直接传递Wrapper
    userMapper.deductBalanceByIds(200, wrapper);
}

public interface UserMapper extends BaseMapper<User> {
    @Select("UPDATE user SET balance = balance - #{money} ${ew.customSqlSegment}")
    void deductBalanceByIds(@Param("money") int money, @Param("ew") QueryWrapper<User> wrapper);
}

IService and ServiceImpl

• save: Add a single element.
• saveBatch: Batch add elements.
• saveOrUpdate: Determine by ID, if the data exists, update it; otherwise, add it.
• saveOrUpdateBatch: Batch add or update.
• removeById: Delete by ID.
• removeByIds: Batch delete by IDs.
• removeByMap: Delete by key-value pairs in the Map.
• remove(Wrapper<T>): Delete by Wrapper condition.
• updateById: Update by ID.
• update(Wrapper<T>): Update by UpdateWrapper, where the Wrapper contains the set and where parts.
• update(T, Wrapper<T>): Update the data matched by Wrapper according to the data in T.
• updateBatchById: Batch update by ID.
• getById: Query one record by ID.
• getOne(Wrapper<T>): Query one record by Wrapper.
• getBaseMapper: Get the BaseMapper implementation within the Service, useful when you need to call custom SQL in the Mapper.
• listByIds: Batch query by IDs.
• list(Wrapper<T>): Query multiple records by Wrapper condition.
• list(): Query all records.
• count(): Count all records.
• count(Wrapper<T>): Count records that meet the Wrapper condition.

public interface IUserService extends IService<User> {
}

@Service
public class UserServiceImpl extends ServiceImpl<UserMapper, User>
}

Lambda in IService

@GetMapping("/list")
@ApiOperation("根据id集合查询用户")
public List<UserVO> queryUsers(UserQuery query){
    // 1.组织条件
    String username = query.getName();
    Integer status = query.getStatus();
    Integer minBalance = query.getMinBalance();
    Integer maxBalance = query.getMaxBalance();
    // 2.查询用户
    List<User> users = userService.lambdaQuery()
            .like(username != null, User::getUsername, username)
            .eq(status != null, User::getStatus, status)
            .ge(minBalance != null, User::getBalance, minBalance)
            .le(maxBalance != null, User::getBalance, maxBalance)
            .list();
    // 3.处理vo
    return BeanUtil.copyToList(users, UserVO.class);
}

• .one(): At most one result.
• .list(): Return a list of results.
• .count(): Return the count of results.

PageHelper

@Configuration
public class MybatisConfig {

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        // 初始化核心插件
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        // 添加分页插件
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

@Test
void testPageQuery() {
    // 1.分页查询，new Page()的两个参数分别是：页码、每页大小
    Page<User> p = userService.page(new Page<>(2, 2));
    // 2.总条数
    System.out.println("total = " + p.getTotal()); //4
    // 3.总页数
    System.out.println("pages = " + p.getPages()); //2
    // 4.数据
    List<User> records = p.getRecords();
    records.forEach(System.out::println);
    
    int pageNo = 1, pageSize = 5;
    // 分页参数
    Page<User> page = Page.of(pageNo, pageSize);
    // 排序参数, 通过OrderItem来指定
    page.addOrder(new OrderItem("balance", false));
    
    userService.page(page);
}