好几把炫酷

入门案例

导入坐标

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.2</version>
</dependency>
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.1.16</version>
</dependency>

yml配置

spring:
  datasource:
    driver-class-name: com.mysql.jdbc.Driver
    username: root
    password: root
    url: jdbc:mysql:///db1?serverTimezone=UTC
    type: com.alibaba.druid.pool.DruidDataSource

数据层接口

接口继承一个mybatisplus写好的mapper。

1
2
3

@Mapper
public interface BookDao extends BaseMapper<Book> {
}

注意，这里搜索的数据库表是按泛型中的类名来搜索的，比如这里就是连接的db1下的book表，如果要更改，要到实体类上添加注解。

1 2	@TableName("tb_book") public class Book {

完成

mybatisplus会自动写好一些sql语句

@SpringBootTest
class MybatisPlusApplicationTests {
    @Autowired
    private BookDao bookDao;

    @Test
    void contextLoads() {
        List<Book> books = bookDao.selectList(null);
        System.out.println(books);
    }

}

标准CRUD制作

@SpringBootTest
class MybatisPlusApplicationTests {
    @Autowired
    private BookDao bookDao;

    @Test
    void testSave(){
        Book book = new Book("111","aaa","ddd");
        bookDao.insert(book);
    }

    @Test
    void testDelete(){
        bookDao.deleteById(5);
    }

    @Test
    void testUpdate(){
        Book book = new Book();
        book.setId(1);
        book.setName("999999");
        bookDao.updateById(book);
    }

    @Test
    void testGetById(){
        Book book = bookDao.selectById(1);
        System.out.println(book);
    }

注意，改操作是一个动态sql语句，可以随意更改。

分页查找

@Test
void testGetByPage() {
    IPage page = new Page(1, 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("一共多少条数据: " + page.getTotal());
    System.out.println("数据: " + page.getRecords());
}

需要配置mybatisplus拦截器

@Configuration
public class MpConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor(){
//        创建mp拦截器
        MybatisPlusInterceptor mybatisPlusInterceptor = new MybatisPlusInterceptor();
//        在mp拦截器中添加分页拦截器
        mybatisPlusInterceptor.addInnerInterceptor(new PaginationInnerInterceptor());
        return mybatisPlusInterceptor;
    }
}

DQL编程控制

条件查询

需要封装wrapper对象

    @Test
    void testByCondition(){
//        按条件查询
//        QueryWrapper queryWrapper = new QueryWrapper();
//        queryWrapper.lt("id",3);
//        List books = bookDao.selectList(queryWrapper);
//        System.out.println(books);

//        lambda格式
//        QueryWrapper<Book> queryWrapper = new QueryWrapper();
//        queryWrapper.lambda().lt(Book::getId,3);
//        List books = bookDao.selectList(queryWrapper);
//        System.out.println(books);

//        lambda格式
//        LambdaQueryWrapper<Book> lambdaQueryWrapper = new LambdaQueryWrapper<>();
//        lambdaQueryWrapper.lt(Book::getId,3);
//        List books = bookDao.selectList(lambdaQueryWrapper);
//        System.out.println(books);

//        多条件查询
      LambdaQueryWrapper<Book> lambdaQueryWrapper = new LambdaQueryWrapper<>();
      lambdaQueryWrapper.lt(Book::getId,2).or().gt(Book::getId,3);
      List books = bookDao.selectList(lambdaQueryWrapper);
      System.out.println(books);
    }

条件查询NULL判定

可在lt，gt方法中添加condition变量，，略过，，

查询投影

QueryWrapper<Book> queryWrapper = new QueryWrapper<Book>();
queryWrapper.select("count(*) as count,description");
queryWrapper.groupBy("description");
List<Map<String, Object>> maps = bookDao.selectMaps(queryWrapper);
System.out.println(maps);

查询条件设置

//        等同
//        LambdaQueryWrapper<Book> lambdaQueryWrapper = new LambdaQueryWrapper<>();
//        lambdaQueryWrapper.eq(Book::getName,"444");
//        Book book = bookDao.selectOne(lambdaQueryWrapper);
//        System.out.println(book);

//        范围查询
//        LambdaQueryWrapper<Book> lambdaQueryWrapper = new LambdaQueryWrapper<>();
//        lambdaQueryWrapper.between(Book::getId,1,4);
//        List<Book> books = bookDao.selectList(lambdaQueryWrapper);
//        System.out.println(books);

//        模糊匹配
        LambdaQueryWrapper<Book> lambdaQueryWrapper = new LambdaQueryWrapper<>();
        lambdaQueryWrapper.like(Book::getType,"2");
        List<Book> books = bookDao.selectList(lambdaQueryWrapper);
        System.out.println(books);