QueryWrapper, mybatisplus 中封裝了大量的查詢方法。用于高級查詢。傳入表的列和查詢的值，就能反射對應的sql. 簡化了查詢。

更多api，查詢使用，看：
https://baomidou.com/guide/wrapper.html

package cn.bitqian;import cn.bitqian.entity.User; import cn.bitqian.mapper.UserMapper; import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper; import org.junit.jupiter.api.Test; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.context.SpringBootTest;import java.util.List;/*** @author echo lovely* @date 2020/11/17 08:19*/@SpringBootTest public class WrapperDemo {@Autowiredprivate UserMapper userMapper;// 測試普通的條件查詢@Testvoid test1() {// 條件構造器QueryWrapper<User> queryWrapper = new QueryWrapper<>();// 查詢name為jack的人 并且年齡大于等于3歲queryWrapper.eq(true,"name", "Jack").ge("age", 3).between("age", 10, 20);User user = userMapper.selectOne(queryWrapper);System.out.println(user);queryWrapper.clear();}// 測試模糊查詢 demo@Testvoid test2() {// 查詢構造器QueryWrapper<User> userWrapper = new QueryWrapper<>();// condition 條件為 false 不包含該條件查詢// LIKE '值%'userWrapper.like("name", "J").likeRight(false, "name", "e");List<User> users = userMapper.selectList(userWrapper);users.forEach(System.out::println);}// 測試子查詢@Testvoid test3() {// ==> Preparing: SELECT id,name,age,email,version,// deleted,gmt_create,gmt_modify FROM user WHERE deleted=0// AND (id IN (select id from user where id < 3))QueryWrapper<User> userWrapper = new QueryWrapper<>();userWrapper.inSql("id", "select id from user where id < 3");List<Object> users = userMapper.selectObjs(userWrapper);users.forEach(System.out::println);}// order by ..@Testvoid test4() {QueryWrapper<User> userWrapper = new QueryWrapper<>();userWrapper.orderByDesc("id");List<User> users = userMapper.selectList(userWrapper);users.forEach(System.out::println);}}

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