lombok

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

    @Test
    void selectById(){
        IPage page = new Page(2,2);
        bookDao.selectPage(page,null);
        System.out.println("当前页码值："+page.getCurrent());
        System.out.println("每页显示数："+page.getSize());
        System.out.println("一共多少页："+page.getPages());
        System.out.println("一共多少数据："+page.getTotal());
        System.out.println("数据："+page.getRecords());
    }

条件查询

方法一：

    @Test
    void selectById(){
        QueryWrapper qw = new QueryWrapper();
        qw.lt("id",3);
        List<Book> list = bookDao.selectList(qw);
        System.out.println(list);
    }

查询id小于3的数据

方法二：lam表达式

    @Test
    void selectById(){
        QueryWrapper<Book> qw = new QueryWrapper();
        qw.lambda().lt(Book::getId,3);
        List<Book> list = bookDao.selectList(qw);
        System.out.println(list);
    }

方法三：

    @Test
    void selectById(){
        LambdaQueryWrapper<Book> lwq = new LambdaQueryWrapper<Book>();
        lwq.lt(Book::getId,3);
        List<Book> list = bookDao.selectList(lwq);
        System.out.println(list);
    }

或

    @Test
    void selectById(){
        LambdaQueryWrapper<Book> lwq = new LambdaQueryWrapper<Book>();
        lwq.lt(Book::getId,3).or().gt(Book::getId,1);
        List<Book> list = bookDao.selectList(lwq);
        System.out.println(list);
    }

且

    @Test
    void selectById(){
        LambdaQueryWrapper<Book> lwq = new LambdaQueryWrapper<Book>();
        lwq.lt(Book::getId,3).gt(Book::getId,1);
        List<Book> list = bookDao.selectList(lwq);
        System.out.println(list);
    }

查询投影

    @Test
    void selectById(){
        BookQuery bookQuery = new BookQuery();
        //bookQuery.setId(1L);
        bookQuery.setId2(3L);

        LambdaQueryWrapper<Book> lwq = new LambdaQueryWrapper<Book>();
        lwq.lt(null!=bookQuery.getId2(),Book::getId,bookQuery.getId2())
                .gt(null!=bookQuery.getId(),Book::getId,bookQuery.getId());
        List<Book> list = bookDao.selectList(lwq);
        System.out.println(list);
    }

相当于将查询参数提出到一个类里，并通过condition参数判断是否满足条件

    @Test
    void selectById(){
        LambdaQueryWrapper<Book> lqw = new LambdaQueryWrapper<>();
        lqw.select(Book::getId,Book::getName,Book::getDescription);
        List<Book> list = bookDao.selectList(lqw);
        System.out.println(list);
    }

    @Test
    void selectById(){
        QueryWrapper<Book> lqw = new QueryWrapper<>();
        lqw.select("count(*)  as count");
        List<Map<String, Object>> list = bookDao.selectMaps(lqw);
        System.out.println(list);
    }

使用map集合来存储非lambda表达式查询结果

    @Test
    void selectById(){
        QueryWrapper<Book> lqw = new QueryWrapper<>();
        lqw.select("count(*)  as count,name");
        lqw.groupBy("name");
        List<Map<String, Object>> list = bookDao.selectMaps(lqw);
        System.out.println(list);
    }

对name进行分组查询

查询条件

    @Test
    void selectById(){
        QueryWrapper<Book> lqw = new QueryWrapper<>();
        lqw.between("id",1,2);
        List<Book> list = bookDao.selectList(lqw);
        System.out.println(list);
    }

    @Test
    void selectById(){
        LambdaQueryWrapper<Book> lwq = new LambdaQueryWrapper<>();
        lwq.like(Book::getName,"t");
        List<Book> list = bookDao.selectList(lwq);
        System.out.println(list);
    }

@TableName("tb_book")
@Data
public class Book {

    private Long id;
    private String name;
    private String type;
    @TableField("description")
    private String description;
    @TableField(exist = false)
    private String online;

}

@TableName与数据库表名对应
@TableField可以与表数据项对应

id生成策略


因为就算数据库的id字段设置自增后，由于idea，必须在对应的实体类中的id字段设置@TableId(type = IdType.AUTO)，才可以实现id自增，不然就算默认的长字符串

@TableName("tb_book")
@Data
public class Book {
    @TableId(type = IdType.AUTO)
    private Long id;
    private String name;
    private String type;
    @TableField("description")
    private String description;
    @TableField(exist = false)
    private String online;

}

用来对tablename进行全局配置
用

mybatis-plus:
  global-config:
    db-config:
      id-type: assign_id

来对idtype（id生成策略进行全局配置）

逻辑删除

    @TableLogic(value = "0",delval = "1")
    private Integer deleted;

可以直接配置 @TableLogic注解来配置逻辑删除，value表示没有删除，delval表示删除
也可以通过

mybatis-plus:
  global-config:
    db-config:
      id-type: assign_id
      logic-delete-field: deleted
      logic-delete-value: 1
      logic-not-delete-value: 0

来配置全局逻辑删除
logic-delete-field：表示逻辑删除字段
logic-not-delete-value：表示未删除的值
logic-delete-value：表示已经删除的值

乐观锁
1.使用注解定义变量

    @Version
    private Integer version;

2.配置拦截器

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
        MybatisPlusInterceptor mybatisPlusInterceptor = new MybatisPlusInterceptor();
        mybatisPlusInterceptor.addInnerInterceptor(new OptimisticLockerInnerInterceptor());
        return mybatisPlusInterceptor;
    }

3.直接把找到的pojo查询再修改

代码生成器