mybatisPlus-wrapper条件构造器

承接:mybatisPlus-性能分析插件

1 在测试包下编写一个新测试类WrapperTest.java

src/test/java/com/lv/mybatis_plus/WrapperTest.java

package com.lv.mybatis_plus;

import com.lv.mybatis_plus.mapper.UserMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
public class WrapperTest {
    @Autowired
    private UserMapper userMapper;
    
}

2 多条件查询

src/test/java/com/lv/mybatis_plus/WrapperTest.java

@Test
void test1() {
    //查询name不为空,邮箱不为空的,并且年龄大于等于12的用户
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper
            .isNotNull("name")
            .isNotNull("email")
            .ge("age",12);
    userMapper.selectList(wrapper).forEach(System.out::println); //和我们刚才学习的map对比一下
}

运行测试查看控制台生成的sql

3 条件查询

src/test/java/com/lv/mybatis_plus/WrapperTest.java

@Test
void test2(){
    //查询名字是可乐
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.eq("name","Tom");
    User user = userMapper.selectOne(wrapper); //查询一个数据,出现多个结果使用List 或者 Map
    System.out.println(user);
}

运行,查看控制台生成的sql

4 区间条件查询

src/test/java/com/lv/mybatis_plus/WrapperTest.java

@Test
void test3(){
    //查询年龄在 22 ~ 25 岁 之间的用户
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.between("age",20,25); //区间
    Integer count = userMapper.selectCount(wrapper);//查询结果数
    System.out.println(count);
}

运行,查看控制台生成的sql

5 模糊查询

src/test/java/com/lv/mybatis_plus/WrapperTest.java

@Test
void test4(){
    //名字里面不包含a的用户
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    // likeRight右边加%,likeLeft左边加%
    wrapper
            .notLike("name","a")
            .likeRight("email","t");
    List<Map<String, Object>> maps = userMapper.selectMaps(wrapper);
    maps.forEach(System.out::println);
}

运行,查看控制台生成的sql

6 拼接子查询sql

src/test/java/com/lv/mybatis_plus/WrapperTest.java

@Test
void test5(){
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    //id 在子查询中查出来
    wrapper.inSql("id","select id from user where id<3");
    List<Object> objects = userMapper.selectObjs(wrapper);
    objects.forEach(System.out::println);
}

运行,查看控制台生成的sql

7 排序查询

src/test/java/com/lv/mybatis_plus/WrapperTest.java

@Test
void test6(){
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    //通过id进行降序排序
    wrapper.orderByDesc("id");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

运行,查看控制台生成的sql

其它的查询方式可以参照官方文档: 条件构造器 | MyBatis-Plus (baomidou.com)