mybatis-plus系统化学习之查询专题

1.背景

查询在实际生产中用得最多,也最灵活.

2.查询案例

表结构:

CREATE TABLE `sys_user` (
  `id` int(32) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `name` varchar(64) DEFAULT NULL,
  `parent_id` int(32) DEFAULT NULL COMMENT '领导id',
  `version` int(64) DEFAULT NULL,
  `gender` int(32) DEFAULT NULL,
  `age` int(32) DEFAULT NULL,
  `position` varchar(64) DEFAULT NULL,
  `account` varchar(255) DEFAULT NULL,
  `password` varchar(225) DEFAULT NULL,
  `status` varchar(64) DEFAULT NULL,
  `create_time` datetime DEFAULT NULL,
  `type` varchar(64) DEFAULT NULL COMMENT '类型',
  `update_time` datetime DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=25 DEFAULT CHARSET=utf8mb4;

需求:

1.最简单的根据id查询
2.根据多个id批量查询
3.map条件查询
条件构造器
4.名字中包含 东平 并且年龄小于等于30
5.名字中包含"东平"并且龄大于等于18且小于等于30并且account不为空
6.名字为姓 "李" 或者 年龄大于等于30，按照年龄降序排列，年龄相同按照id升序排列
7.查询年龄大于等于18岁,并且领导为 张三丰 的员工
8.查询姓"李" 并且 (年龄小于30 或 account不为空）
9.查询姓"李"  或者 (年龄小于30 并且 account不为空）
10.查询(年龄小于30 或者 account不为空) 并且 姓"李"
11.查询年龄大于18岁的
12查询(年龄大于15岁并且有领导的员工)按照领导分组，每组的平均年龄、最大年龄、最小年龄,并且只取平均年龄大于18的组。
13.lambda构造器(最大的优点就是列名写错了有提示,用户与普通的QueryWrapper用法一样)
 查询姓"李"  并且 年龄小于30

实现代码:

package com.ldp.demo01;

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.ldp.entity.SysUser;
import com.ldp.mapper.SysUserMapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;

/**
 * @author 姿势帝-博客园
 * @address https://www.cnblogs.com/newAndHui/
 * @WeChat 851298348
 * @create 11/06 10:27
 * @description <p>
 * 在讲查询的时候,我先把实体与表还原成最初的样子(即重新导入表结构和数据java实体),避免造成学习干扰
 * 这个章节将系统化的讲解查询
 * 需求如下:
 * 最简单的根据id查询
 *
 * </p>
 */
@RunWith(SpringRunner.class)
@SpringBootTest
public class Test03Select {
    @Autowired
    private SysUserMapper sysUserMapper;

    /**
     * 最简单的根据id查询
     * <p>
     * ==>  Preparing: SELECT id,version,age,gender,name,position,account,password,status,type,create_time,update_time FROM sys_user WHERE id=?
     * ==> Parameters: 20(Integer)
     */
    @Test
    public void selectById() {
        SysUser sysUser = sysUserMapper.selectById(20);
        System.out.println("sysUser=" + sysUser);
    }

    /**
     * 根据多个id批量查询
     * <p>
     * ==>  Preparing: SELECT id,version,age,gender,name,position,account,password,status,type,create_time,update_time FROM sys_user WHERE id IN ( ? , ? , ? , ? )
     * ==> Parameters: 17(Integer), 18(Integer), 19(Integer), 20(Integer)
     */
    @Test
    public void selectBatchIds() {
        List<Integer> asList = Arrays.asList(17, 18, 19, 20);
        List<SysUser> sysUsers = sysUserMapper.selectBatchIds(asList);
        System.out.println("list=" + sysUsers);
    }

    /**
     * map条件查询
     * 注意:map条件中的key是用数据库中的字段对应,而不是与java中的实体对应
     * ==>  Preparing: SELECT id,version,age,gender,name,position,account,password,status,type,create_time,update_time FROM sys_user WHERE name = ? AND age = ?
     * ==> Parameters: 李东平(String), 18(String)
     */
    @Test
    public void selectByMap() {
        Map<String, Object> columnMap = new HashMap<>();
        columnMap.put("name", "李东平");
        columnMap.put("age", "18");
        // columnMap 拼接的条件为 WHERE name = ? AND age = ?
        List<SysUser> sysUsers = sysUserMapper.selectByMap(columnMap);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 条件构造器
     * <p>
     * 1、名字中包含 东平 并且年龄小于等于30
     * name like '%东平%' and age<=30
     * ==>  Preparing: SELECT id,version,age,gender,name,position,account,password,status,type,create_time,update_time FROM sys_user
     * WHERE (name LIKE ? AND age <= ?)
     * ==> Parameters: %东平%(String), 30(Integer)
     * <p>
     * 备注:
     * 等于的英语单词是:equals
     * 小于的英文:less than
     * le表示小于等于 <=
     * lt表示小于 <
     * <p>
     * 同样的道理
     * 大于的英文为 greater than
     * gt 表示大于 >
     * ge 表示大于等于 >=
     */
    @Test
    public void testQueryWrapper1() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.like("name", "东平");
        queryWrapper.le("age", 30);
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 名字中包含"东平"并且龄大于等于18且小于等于30并且account不为空
     * ==>  Preparing: SELECT id,version,age,gender,name,position,account,password,status,type,create_time,update_time
     * FROM sys_user WHERE (name LIKE ? AND age >= ? AND age <= ? AND account IS NOT NULL)
     * ==> Parameters: %东平%(String), 30(Integer), 40(Integer)
     */
    @Test
    public void testQueryWrapper2() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.like("name", "东平");
        queryWrapper.ge("age", 30);
        queryWrapper.le("age", 40);
        // condition = true表示加上这个条件, condition = false表示  不 加上这个条件
        queryWrapper.isNotNull(true, "account");
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 名字为姓 "李" 或者 年龄大于等于30，按照年龄降序排列，年龄相同按照id升序排列
     * ==>  Preparing: SELECT id,version,age,gender,name,position,account,password,status,type,create_time,update_time
     * FROM sys_user WHERE (name LIKE ? OR age >= ?) ORDER BY age DESC,id ASC
     * ==> Parameters: 李%(String), 30(Integer)
     */
    @Test
    public void testQueryWrapper3() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.likeRight(true, "name", "李");
        queryWrapper.or();
        queryWrapper.ge("age", 30);
        queryWrapper.orderByDesc("age");
        queryWrapper.orderByAsc("id");
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 查询年龄大于等于18岁,并且领导为 张三丰 的员工
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE (age >= ? AND parent_id in (select id from sys_user where `name`=?))
     * ==> Parameters: 18(Integer), 张三丰(String)
     */
    @Test
    public void testQueryWrapper4() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.ge("age", 18);
        // 特别注意 这个地方不需要在写 and ,参数下标从0开始
        queryWrapper.apply("parent_id in (select id from sys_user where `name`={0})", "张三丰");
        List list = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + list);
    }

    /**
     * 查询姓"李" 并且 (年龄小于30 或 account不为空）
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE (name LIKE ? AND (age < ? OR account IS NOT NULL))
     * ==> Parameters: 李%(String), 30(Integer)
     */
    @Test
    public void testQueryWrapper5() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.likeRight(true, "name", "李");
        // 嵌套条件
        Consumer<QueryWrapper> consumer = queryWrapper2 -> {
            queryWrapper2.lt("age", 30);
            queryWrapper2.or();
            queryWrapper2.isNotNull("account");
        };
        queryWrapper.and(consumer);
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 第二种实现
     * 嵌套条件这好,个人建议使用这种,自己写条件sql,更直观好理解
     * 查询姓"李" 并且 (年龄小于30 或 account不为空）
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE (name LIKE ? AND (age < ? OR account IS NOT NULL))
     * ==> Parameters: 李%(String), 30(Integer)
     */
    @Test
    public void testQueryWrapper52() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.likeRight(true, "name", "李");
        queryWrapper.apply(" (age < {0} OR account IS NOT NULL)", 30);
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 方式一
     * 查询姓"李"  或者 (年龄小于30 并且 account不为空）
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE (name LIKE ? OR (age < ? and account IS NOT NULL))
     * ==> Parameters: 李%(String), 30(Integer)
     */
    @Test
    public void testQueryWrapper6() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.likeRight(true, "name", "李");
        // 嵌套条件
        Consumer<QueryWrapper> consumer = queryWrapper2 -> {
            queryWrapper2.lt("age", 30);
            queryWrapper2.isNotNull("account");
        };
        queryWrapper.or(consumer);
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 方式二
     * 查询姓"李"  或者 (年龄小于30 并且 account不为空）
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE (name LIKE ? OR (age < ? and account IS NOT NULL))
     * ==> Parameters: 李%(String), 30(Integer)
     */
    @Test
    public void testQueryWrapper62() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.likeRight(true, "name", "李");
        queryWrapper.or();
        queryWrapper.apply(" (age < {0} and account IS NOT NULL)", 30);
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 查询(年龄小于30 或者 account不为空) 并且 姓"李"
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE ((age < ? OR account IS NOT NULL) AND name LIKE ?)
     * ==> Parameters: 30(Integer), 李%(String)
     */
    @Test
    public void testQueryWrapper7() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        // 嵌套条件
        Consumer<QueryWrapper> consumer = queryWrapper2 -> {
            queryWrapper2.lt("age", 30);
            queryWrapper2.or();
            queryWrapper2.isNotNull("account");
        };
        queryWrapper.and(consumer);
        queryWrapper.likeRight("name", "李");
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 方式二写sql的方式
     * 查询(年龄小于30 或者 account不为空) 并且 姓"李"
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE ((age < ? OR account IS NOT NULL) AND name LIKE ?)
     * ==> Parameters: 30(Integer), 李%(String)
     */
    @Test
    public void testQueryWrapper72() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        // 嵌套条件
        queryWrapper.apply(" (age < {0} OR account IS NOT NULL)", 30);
        queryWrapper.likeRight("name", "李");
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

    /**
     * 查询年龄大于18岁的
     */
    @Test
    public void testQueryWrapper8() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.eq("age", 15);
        queryWrapper.eq("name", "张无忌");
        // 返回多条会报错,只返回一条或者无数据不报错,sql语句中没有limit
        SysUser sysUser = sysUserMapper.selectOne(queryWrapper);
        System.out.println("sysUser=" + sysUser);
    }

    /**
     * <p>
     * 查询(年龄大于15岁并且有领导的员工)按照领导分组，每组的平均年龄、最大年龄、最小年龄,并且只取平均年龄大于18的组。
     * <p>
     * ==>  Preparing: SELECT parent_id,AVG(age) avg,MAX(age) max,MIN(age) min FROM sys_user WHERE (age > ? AND parent_id IS NOT NULL) GROUP BY parent_id HAVING AVG(age)>?
     * ==> Parameters: 15(Integer), 18(Integer)
     * <==    Columns: parent_id, avg, max, min
     * <==        Row: 1, 58.5455, 99, 18
     * <==      Total: 1
     */
    @Test
    public void test9() {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        // 需要查询的列
        queryWrapper.select("parent_id", "AVG(age) avg", "MAX(age) max", "MIN(age) min");
        // 查询条件
        queryWrapper.gt("age", 15);
        queryWrapper.isNotNull("parent_id");
        // 分组
        queryWrapper.groupBy("parent_id");
        // 分组后的条件
        queryWrapper.having("AVG(age)>{0}", 18);
        // 执行查询
        List list = sysUserMapper.selectMaps(queryWrapper);
        System.out.println("list=" + list);
    }

    /**
     * lambda构造器(最大的优点就是列名写错了有提示,用户与普通的QueryWrapper用法一样)
     * 查询姓"李"  并且 年龄小于30
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE (name LIKE ? AND age < ?)
     * ==> Parameters: 李%(String), 30(Integer)
     */
    @Test
    public void test10() {
        LambdaQueryWrapper<SysUser> queryWrapper = new LambdaQueryWrapper<>();
        queryWrapper.likeRight(SysUser::getName, "李");
        queryWrapper.lt(SysUser::getAge, 30);
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

}

3.高级查询条件

代码:

 /**
     * 高级查询条件控制
     * 需求:
     * 实际生产中我们要求传入了参数则加入where 条件,否则不加入
     * 查询姓 "李" 的员工
     */
    @Test
    public void test1() {
        String name = "";
        methodTest1(name);
    }

    /**
     * name 有值时才加入条件
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user
     * ==> Parameters:
     *
     * @param name
     */
    public void methodTest1(String name) {
        QueryWrapper queryWrapper = new QueryWrapper<SysUser>();
        queryWrapper.like(!StrUtil.isEmpty(name), "name", name);
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

4.java实体作为条件

1.使用默认的=#{}作为where条件

    /**
     * java实体作为条件
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE age=? AND name=?
     * ==> Parameters: 18(Integer), 张无忌(String)
     */
    @Test
    public void test2() {
        SysUser sysUser = new SysUser().setName("张无忌").setAge(18);
        QueryWrapper queryWrapper = new QueryWrapper<>(sysUser);

        //queryWrapper.setEntity(sysUser);
        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

2.修改默认的条件方式

首先在字段name上加注解

然后代码如下:

 /**
     * java实体作为条件(修改默认条件方式)
     * 例如name要求以like作为条件(如果SqlCondition常量中没有的,可以自己增加)
     * @TableField(condition = SqlCondition.LIKE)
     * private String name;
     *
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE name LIKE CONCAT('%',?,'%')
     * ==> Parameters: 无忌(String)
     */
    @Test
    public void test2_1() {
        SysUser sysUser = new SysUser().setName("无忌");
        QueryWrapper queryWrapper = new QueryWrapper<>(sysUser);
        //queryWrapper.setEntity(sysUser);

        List<SysUser> sysUsers = sysUserMapper.selectList(queryWrapper);
        System.out.println("list=" + sysUsers);
    }

5.使用原来的mybatis写sql实现

1.在SysUserMapper中添加接口

    /**
     * 查询用户列表(mybatis自己写sql的方式)
     *
     * @param sysUser
     * @return
     */
    List<SysUser> queryListUser(@Param("sysUser") SysUser sysUser);

2.编写xml的sql

    <select id="queryListUser" resultType="com.ldp.entity.SysUser">
     SELECT * FROM sys_user
     <where>
         <if test="sysUser.name!=null and sysUser.name!=''">
             name = #{sysUser.name}
         </if>
     </where>
    </select>

3.使用

    /**
     * 自己写sql实现
     * ==>  Preparing: SELECT * FROM sys_user WHERE name = ?
     * ==> Parameters: 李东平(String)
     */
    @Test
    public void test1() {
        SysUser sysUser = new SysUser().setName("李东平");
        List<SysUser> list = sysUserMapper.queryListUser(sysUser);
        System.out.println("list=" + list);
    }

6.使用Wrapper自定义SQL

这种方式在实际生产中一般不用,大家知道有这知识点就可以了.

1.在SysUserMapper中编写接口和sql

    /**
     * 使用 Wrapper 自定义SQL
     *
     * @param queryWrapper
     * @return 注意:
     * 1. Constants.WRAPPER = ew
     * 2. sql语句也可以写在xml中(这里不演示)
     * 3. sql语句中没有where
     */
    @Select("select * from sys_user ${ew.customSqlSegment}")
    List<SysUser> selectListMy(@Param("ew") Wrapper<SysUser> queryWrapper);

2.使用

  /**
     * 使用 Wrapper 自定义SQL
     * ==>  Preparing: SELECT * FROM sys_user WHERE name = ?
     * ==> Parameters: 李东平(String)
     */
    @Test
    public void test2() {
        QueryWrapper<SysUser> wrapper = new QueryWrapper<SysUser>().lt("age", 50);
        List<SysUser> list = sysUserMapper.selectListMy(wrapper);
        System.out.println("list=" + list);
    }

7.分页查询

1.添加一个MybatisPlusConfig配置文件代码

package com.ldp.config;

import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author 姿势帝-博客园
 * @address https://www.cnblogs.com/newAndHui/
 * @WeChat 851298348
 * @create 12/06 4:45
 * @description
 */
@Configuration
@MapperScan("com.ldp.mapper")
public class MybatisPlusConfig {
    /**
     * 分页插件
     *
     * @return
     */
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        PaginationInterceptor paginationInterceptor = new PaginationInterceptor();
        return paginationInterceptor;
    }
}

2.使用

    /**
     * 分页测试
     * 查询一共有多少条
     * ==>  Preparing: SELECT COUNT(1) FROM sys_user WHERE (age < ?)
     * ==> Parameters: 60(Integer)
     *
     * 查询列表
     * ==>  Preparing: SELECT id,version,age,gender,name,parent_id,position,account,password,status,type,create_time,update_time FROM sys_user WHERE (age < ?) LIMIT ?,?
     * ==> Parameters: 60(Integer), 4(Long), 2(Long)
     */
    @Test
    public void test1() {
        QueryWrapper<SysUser> wrapper = new QueryWrapper<>();
        wrapper.lt("age",60);
        Page<SysUser> page = new Page<>(3,2);
        IPage<SysUser> pageResult = sysUserMapper.selectPage(page, wrapper);
        System.out.println("list=" + pageResult.getRecords());
    }

3.自己写sql的分页

a.编写接口

/**
     * 自己写sql实现分页
     * @param sysUser
     * @return
     */
    IPage<SysUser> queryPage(Page<SysUser> page,@Param("sysUser") SysUser sysUser);

b.编写sql

    <select id="queryPage" resultType="com.ldp.entity.SysUser">
        SELECT * FROM sys_user
        <where>
            <if test="sysUser.name!=null and sysUser.name!=''">
                name = #{sysUser.name}
            </if>
        </where>
    </select>

c.使用

/**
     * 测试自己的sql分页
     */
    @Test
    public void test2() {
        SysUser sysUser = new SysUser().setName("");
        Page<SysUser> page = new Page<>(3,2);
        IPage<SysUser> pageResult = sysUserMapper.queryPage(page,sysUser);
        System.out.println("list=" + pageResult.getRecords());
    }

mybatis-plus系统化学习教程：https://www.cnblogs.com/newAndHui/p/14141950.html

完美!