MybatisPlus的各种查询方式！

目录

• 基本查询
• 条件构造器查询
• 指定列与排除列
• Condition处理参数
• 以实体作为参数
• AllEq的使用
• 自定义查询
  • 注解形式
  • xml形式
• 其他的查询

注：本文代码样例及sql脚本均已上传至gitee：spring-boot-mybatis-plus学习

基本查询

    /**
     * id=?
     */
    @Test
    void selectById() {
        User user = mapper.selectById(1087982257332887553L);
        System.out.println(user);
    }

    /**
     * id IN ( ? , ? , ? )
     */
    @Test
    void retrieveByIds() {
        List<User> users = mapper.selectBatchIds(Arrays.asList(8, 9, 10));
        users.forEach(System.out::println);
    }

    /**
     * 根据map查询,key为column,value为具体的值
     * name = ? AND age = ?
     */
    @Test
    void retrieveByMap() {
        Map<String, Object> map = new HashMap<>();
        map.put("name", "大boss");
        map.put("age", "40");
        List<User> users = mapper.selectByMap(map);
        users.forEach(System.out::println);
    }

条件构造器查询

地址: 条件构造器

    /**
     * 名字中包含雨并且年龄小于40
     * name like '%雨%' and age<40
     */
    @Test
    void selectByWrapper1() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.like("name", "雨")
                .lt("age", 40);
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

    /**
     * 名字中包含雨年并且龄大于等于20且小于等于40并且email不为空
     * name like '%雨%' and age between 20 and 40 and email is not null
     */
    @Test
    void selectByWrapper2() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.like("name", "雨")
                .between("age", 20, 40)
                .isNotNull("email");
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

    /**
     * 名字为王姓或者年龄大于等于25，按照年龄降序排列，年龄相同按照id升序排列
     * name like '王%' or age>=25 order by age desc,id asc
     */
    @Test
    void selectByWrapper3() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.likeRight("name", "王")
                .or().ge("age", 25)
                .orderByDesc("age")
                .orderByAsc("id");
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

    /**
     * 创建日期为2019年2月14日并且直属上级为名字为王姓
     * date_format(create_time,'%Y-%m-%d')='2019-02-14' and
     * manager_id in (select id from user where name like '王%')
     */
    @Test
    void selectByWrapper4() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.apply("date_format(create_time,'%Y-%m-%d')={0}", "2019-02-14")
                .inSql("manager_id", "select id from user where name like '王%'");
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }


    /**
     * and中传入lambda
     * <p>
     * 名字为王姓并且（年龄小于40或邮箱不为空）
     * name like '王%' and (age<40 or email is not null)
     */
    @Test
    void selectByWrapper5() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.likeRight("name", "王").
                and(wq -> wq.lt("age", 40)
                        .or().isNotNull("email"));
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

    /**
     * 名字为王姓或者（年龄小于40并且年龄大于20并且邮箱不为空）
     * name like '王%' or (age<40 and age>20 and email is not null)
     */
    @Test
    void selectByWrapper6() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.likeRight("name", "王").
                or(wq -> wq.lt("age", 40)
                        .gt("age", 20)
                        .isNotNull("email"));
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

    /**
     * （ 年龄小于40或邮箱不为空）并且名字为王姓
     * (age<40 or email is not null) and name like '王%'
     */
    @Test
    void selectByWrapper7() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.nested(wq -> wq.lt("age", 40)
                .or().isNotNull("email"))
                .likeRight("name", "王");
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }


    /**
     * 年龄为30、31、34、35
     */
    @Test
    void selectByWrapper8() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.in("age", Arrays.asList(30, 31, 34, 35));
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

    /**
     * 只返回满足条件的其中一条语句即可  limit 1
     */
    @Test
    void selectByWrapper9() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.in("age", Arrays.asList(30, 31, 34, 35)).last("limit 1");
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

指定列与排除列

    /**
     * 查询指定列
     * SELECT id,name FROM user WHERE (name LIKE ?)
     */
    @Test
    void selectPart1() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.select("id", "name").like("name", "雨");
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

    /**
     * 排除指定列
     * SELECT id,name,age,manager_id FROM user WHERE (name LIKE ?)
     */
    @Test
    void selectPart2() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.select(User.class, info -> !info.getColumn().equals("create_time") &&
                !info.getColumn().equals("email")
        ).like("name", "雨");
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

Condition处理参数

    @Test
    void testCondition(){
        String name = "王";
        String email = "";
        //withOutCondition(name,email);
        withCondition(name,email);
    }

    private void withOutCondition(String name,String email){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        if(StringUtils.isNotBlank(name)){
            wrapper.like("name",name);
        }
        if(StringUtils.isNotBlank(email)){
            wrapper.like("email",email);
        }
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }
    private void withCondition(String name,String email){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.like(StringUtils.isNotBlank(name),"name",name)
                .like(StringUtils.isNotBlank(email),"email",email);
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

以实体作为参数

    /**
     * WHERE name=? AND age=?
     * 以实体为参数 和普通设置参数 互不干扰, 都会存在, 使用时需慎重
     * 以实体为参数,默认是等值的,需要使用@TableField注解,并注明sqlCondition
     */
    @Test
    void selectByWrapperEntity(){
        User user = new User();
        user.setName("天乔巴夏");
        user.setAge(20);
        QueryWrapper<User> wrapper = new QueryWrapper<>(user);
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }


    @TableField(value = "name",condition = SqlCondition.LIKE) //指定字段名
    private String name;

AllEq的使用

    @Test
    void selectByWrapperAllEq(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        Map<String,Object> params = new HashMap<>();
        params.put("name","天乔巴夏");
        params.put("age",null); // age is null , 可以通过 下面这句设置 false
        wrapper.allEq(params,false);
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

    @Test
    void selectByWrapperAllEq2() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        Map<String, Object> params = new HashMap<>();
        params.put("name", "天乔巴夏");
        params.put("age", null); // age is null , 可以通过 下面这句设置 false
        wrapper.allEq((k, v) -> !k.equals("name"), params, false);
        List<User> users = mapper.selectList(wrapper);
        users.forEach(System.out::println);
    }

自定义查询

注解形式

public interface UserMapper extends BaseMapper<User> {

    @Select("select * from user ${ew.customSqlSegment}")
    List<User>  selectAll(@Param(Constants.WRAPPER)Wrapper<User> wrapper);

}

    /**
     * 测试自定义方法 注解
     */
    @Test
    void selectByCustomAnno(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.eq("name","天乔巴夏");
        List<User> users = mapper.selectAll(wrapper);
        users.forEach(System.out::println);
    }

xml形式

public interface UserMapper extends BaseMapper<User> {

    List<User>  selectAll2(@Param(Constants.WRAPPER)Wrapper<User> wrapper);

}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.hyh.mybatisplus.mapper.UserMapper">

    <select id="selectAll2" resultType="com.hyh.mybatisplus.entity.User">
        select * from user ${ew.customSqlSegment}
    </select>
</mapper>

其他的查询

    /**
     * 优雅返回指定字段的结果
     */
    @Test
    void selectByWrapperMaps1() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.like("name", "雨")
                .lt("age", 40)
        .select("id","name");
        List<Map<String, Object>> mapList = mapper.selectMaps(wrapper);
        mapList.forEach(System.out::println);
    }


    /**
     * 按照直属上级分组，查询每组的平均年龄、最大年龄、最小年龄。
     * 并且只取年龄总和小于500的组。
     *
     * select avg(age) avg_age,min(age) min_age,max(age) max_age
     * from user
     * group by manager_id
     * having sum(age) <500
     */
    @Test
    void selectByWrapperMaps2() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.select("avg(age) avg_age","min(age) min_age","max(age) max_age")
                .groupBy("manager_id").having("sum(age)<{0}",500);
        List<Map<String, Object>> mapList = mapper.selectMaps(wrapper);
        mapList.forEach(System.out::println);
    }

    /**
     * 只返回一列
     */
    @Test
    void selectByWrapperObjs() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.select("avg(age) avg_age","min(age) min_age","max(age) max_age")
                .groupBy("manager_id").having("sum(age)<{0}",500);
        List<Object> objects = mapper.selectObjs(wrapper);
        objects.forEach(System.out::println);
    }


    /**
     * 查个数
     */
    @Test
    void selectCount() {
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.like("name","雨");
        Integer cnt = mapper.selectCount(wrapper);
        System.out.println(cnt);
    }

    /**
     * 查一个实体
     */
    @Test
    void selectOne(){
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.eq("name","天乔巴夏");
        User user = mapper.selectOne(wrapper);
        System.out.println(user);
    }

    /**
     * lambda构造,编译时检查字段信息,防止误写
     */
    @Test
    void selectLambda(){
        //LambdaQueryWrapper<User> lambda = new QueryWrapper<User>().lambda();
        //LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();
        LambdaQueryWrapper<User> lambdaQuery = Wrappers.<User>lambdaQuery();
        lambdaQuery.like(User::getName,"雨").lt(User::getAge,40);
        // where name like '%雨%'
        List<User> users = mapper.selectList(lambdaQuery);
        users.forEach(System.out::println);
    }