数据层，业务层开发简单流程

数据层

1、使用lombok @Data快速定义实体类

package com.tj.domain;
import lombok.Data;
//实体类
@Data
public class Users {
    private Integer id;
    private Integer isuse;
    private String user_id;
    private String password;
    private String user_name;
}

2、继承MP的BaseMapper的方法类，可以自定义其他的接口方法

package com.tj.dao;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.tj.domain.Users;
import org.apache.ibatis.annotations.Mapper;
import org.springframework.stereotype.Repository;
@Mapper
@Repository
public interface UsersDao extends BaseMapper<Users> {
   //除了继承，还可以自定义接口，名称不要和继承相同否则会覆盖
}

业务层

1、继承MP的通用接口IService的方法

package com.tj.service;
import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.service.IService;
import com.tj.domain.Users;
public interface IUserService extends IService<Users> {
    IPage<Users> getPage(int pagenum, int pagesize, Users user);
}

2、extends 通用实现类ServiceImpl implements IUserService实现类

package com.tj.service.impl;
import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.tj.dao.UsersDao;
import com.tj.domain.Users;
import com.tj.service.IUserService;
import org.apache.logging.log4j.util.Strings;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl extends ServiceImpl<UsersDao, Users> implements IUserService {
    @Autowired
    private UsersDao usersDao;
    //分页查询
    @Override
    public IPage<Users> getPage(int pagenum, int pagesize, Users user) {
        //查询条件
        LambdaQueryWrapper<Users> lqw = new LambdaQueryWrapper<>();
        //user_id
        lqw.like(Strings.isNotEmpty(user.getUser_id()), Users::getUser_id, user.getUser_id());
        //and id
        lqw.like(user.getId() != null, Users::getId, user.getId());
        //and user_and
        lqw.like(Strings.isNotEmpty(user.getUser_name()), Users::getUser_name, user.getUser_name());
        IPage page = new Page(pagenum, pagesize);
        usersDao.selectPage(page, lqw);
        return page;
    }
}

3、测试业务层

package com.tj.dao.service;
import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.tj.domain.Users;
import com.tj.service.IUserService;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import java.util.List;
@SpringBootTest
public class UserServiceTest {
    @Autowired
    private IUserService userService;
    @Test
    void testGetById() {
        System.out.println(userService.getById(2));
    }
    @Test
    void testSave() { //新增
        Users user = new Users();
        user.setId(10);
        user.setIsuse(0);
        user.setUser_id("ceshi");
        user.setUser_name("测试");
        user.setPassword("87976494d664ds46dfsd6f4sfsfsd");
        userService.saveOrUpdate(user);
    }
    @Test
    void testModify() { //修改
        Users user = new Users();
        user.setId(10);
        user.setIsuse(0);
        user.setUser_id("xiug");
        user.setUser_name("测试xiugai");
        user.setPassword("87976494d664ds46dfsd6f4sfsfsd");
        userService.updateById(user);
    }
    @Test
    void testDelete() { //删除
        userService.removeById(10);
    }
    @Test
    void testGetPage() { //分页查询
        IPage<Users> page = new Page<Users>(3, 5);
        userService.page(page,null);
        long current = page.getCurrent();//当前页
        long pages = page.getPages();//总页数
        long size = page.getSize();//每页显示几条
        long total = page.getTotal();//总条数
        List records = page.getRecords();//  分页对象记录列表
    }
    @Test
    void testGetBy() {  //按条件查询
        LambdaQueryWrapper<Users> lqw = new LambdaQueryWrapper<>();
        String name = "1";
        String name2 = "2";
        String name3 = "3";
        lqw.like(name3 != null, Users::getUser_name, name3);
        lqw.and(e -> {
            e.like(name != null, Users::getUser_name, name).or();
            e.like(name2 != null, Users::getUser_name, name2);
        });
        //等于 WHERE (user_name LIKE ? AND (user_name LIKE ? OR user_name LIKE ?))
        List<Users> userList = userService.list(lqw);
    }
}