mybatisplus查询练习代码

package com.yase;import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.yase.entity.Student;
import com.yase.entity.Teacher;
import com.yase.mapper.StudentMapper;
import com.yase.mapper.TeacherMapper;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;import javax.annotation.Resource;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;@SpringBootTest
public class TestSelect {@Resourceprivate TeacherMapper mapper;@Resourceprivate StudentMapper studentMapper;@Testpublic void selectById(){Teacher teacher = mapper.selectById(105);System.out.println(teacher);}@Testpublic void selectByIds(){List<Teacher> list = mapper.selectBatchIds(Arrays.asList(105, 106, 107));list.forEach(System.out::println);}@Testpublic void selectByMap(){Map<String,Object> map = new HashMap<>();map.put("teacher_name","李四");map.put("gender","女");List<Teacher> list = mapper.selectByMap(map);list.forEach(System.out::println);}@Testpublic void exists(){QueryWrapper<Teacher> wrapper = new QueryWrapper<>();wrapper.eq("teacher","张三");boolean exists = mapper.exists(wrapper);System.out.println(exists);}@Testpublic void count(){QueryWrapper<Teacher> wrapper =new QueryWrapper<>();wrapper.like("teacher_name","张");Long aLong = mapper.selectCount(wrapper);System.out.println(aLong);}@Testpublic void selectMaps(){QueryWrapper<Teacher> wrapper = new QueryWrapper<>();wrapper.like("teacher","张");List<Map<String, Object>> list = mapper.selectMaps(wrapper);list.forEach(map->map.forEach((key,value) -> System.out.println(key+" "+value)));}//只返回第一个字段的值@Testpublic void selectObjs(){QueryWrapper<Teacher> wrapper = new QueryWrapper<>();wrapper.like("teacher_name","张");List<Object> objects = mapper.selectObjs(wrapper);objects.forEach(System.out::println);}@Testpublic void selectList() {//查询全部数据，返回list<teacher>List<Teacher> list = mapper.selectList(null);list.forEach(System.out::println);}//and查询方式@Testpublic void selectList1() {QueryWrapper<Teacher> wrapper = new QueryWrapper<>();wrapper.like("teacher_name", "张").eq("gender", "女");List<Teacher> list = mapper.selectList(wrapper);list.forEach(System.out::println);}//or查询方式@Testpublic void selectList2() {QueryWrapper<Teacher> wrapper = new QueryWrapper<>();wrapper.like("teacher_name", "张").or().eq("gender", "女");List<Teacher> list = mapper.selectList(wrapper);list.forEach(System.out::println);}//查询性别是女，并且年龄大于23的女性@Testpublic void selectList3() {QueryWrapper<Teacher> wrapper = new QueryWrapper<>();wrapper.like("teacher_name", "张").eq("gender", "女").or().gt("age", 23);List<Teacher> list = mapper.selectList(wrapper);list.forEach(System.out::println);}//查询性张，并且（性别是女年龄大于23的女性）用and包括@Testpublic void selectList4() {QueryWrapper<Teacher> wrapper = new QueryWrapper<>();wrapper.likeRight("teacher_name", "张").and(i -> i.eq("gender", "女").or().gt("age", 23));List<Teacher> list = mapper.selectList(wrapper);list.forEach(System.out::println);}//按照年龄排序,相同用id降序排序@Testpublic void selectListOrderBy() {QueryWrapper<Teacher> wrapper = new QueryWrapper<>();wrapper.orderByDesc("age").orderByDesc("id");List<Teacher> list = mapper.selectList(wrapper);list.forEach(System.out::println);}//子查询@Testpublic void selectListSub() {QueryWrapper<Student> wrapper = new QueryWrapper<>();wrapper.inSql("tid", " select id from teacher where teacher_name = '张老师'");List<Student> students = studentMapper.selectList(wrapper);students.forEach(System.out::println);}//分页插件@Testpublic void selectPage() {//需要在构造方法里传入2个参数，一个页码，一个每页数量Page<Student> page = new Page<>(1, 5);QueryWrapper<Student> wrapper = new QueryWrapper<>();wrapper.likeRight("student_name", "李");//page里真正的数据List<Student> records = page.getRecords();records.forEach(System.out::println);studentMapper.selectPage(page, wrapper);System.out.println("总记录数：" + page.getTotal() +"总页数" + page.getPages() +"当前页数" + page.getCurrent() +"每页显示" + page.getSize() + "条数据" +"是否有上一页" + page.hasPrevious() +    //bollean"是否有下一页" + page.hasNext()         //bollean);}@Testpublic void selectMapsPage(){Page<Map<String,Object>> page = new Page<>(1, 5);QueryWrapper<Student> wrapper = new QueryWrapper<>();wrapper.likeRight("student_name", "李");studentMapper.selectMapsPage(page, wrapper);//page里真正的数据List<Map<String,Object>> records = page.getRecords();records.forEach(map->map.forEach((key,value)-> System.out.println(key+" "+value)));System.out.println("总记录数：" + page.getTotal() +"总页数" + page.getPages() +"当前页数" + page.getCurrent() +"每页显示" + page.getSize() + "条数据" +"是否有上一页" + page.hasPrevious() +    //bollean"是否有下一页" + page.hasNext()         //bollean);}//自定义查询@Testpublic void selectCustomer(){List<Student> list = studentMapper.selectCustomer();list.forEach(System.out::println);}}