QueryDsl自定义返回对象，接收分页排序参数，引用Mysql函数等示例

写在前面

记录在queryDsl使用过程中的一些实现，关于JPA集成queryDsl，以及自定义存储库的问题，这里就不详细介绍了，主要总结下QueryDsl的一些使用问题，可参考我上文总结，链接这里

一、自定义返回对象

在我们集成queryDsl时，一般是这样用的

    @Override
    public List<CityHotelVo> findcityHotel() {
        JPAQuery<CityHotelVo> query = new JPAQuery<>(em);
        QTCity c = QTCity.tCity;
        QTHotel h = QTHotel.tHotel;

        JPAQuery<Tuple> on = query.select(
                c.id,
                c.name,
                h.name,
                h.address).from(c).leftJoin(h).on(c.id.eq(h.city));

        QueryResults<Tuple> rts = on.fetchResults();
        List<Tuple> results = rts.getResults();

        return results.stream().map(CityHotelVo::new).collect(Collectors.toList());
    }

转Vo实现

    public CityHotelVo(Tuple t) {
        this.id = t.get(QTCity.tCity.id);
        this.cityName = t.get(QTCity.tCity.name);
        this.hotelName = t.get(QTHotel.tHotel.name);
        this.address = t.get(QTHotel.tHotel.address);
    }

返回的是一个List，我们还需将tuple手动转成我们自定义的VO对象,以下总结了可自动Tuple转VO的几种实现。

1.1、方式一

    /**
     * 方式一：使用Bean投影
     * todo 这里暂未调通
     * @return
     */
    @Override
    public List<CityHotelVo> findcityHotel_2() {
        JPAQuery<CityHotelVo> query = new JPAQuery<>(em);
        QTCity c = QTCity.tCity;
        QTHotel h = QTHotel.tHotel;

        List<CityHotelVo> results1 = query.select(Projections.bean(CityHotelVo.class,
                c.id.as("id"),
                c.name.as("cityName"),
                h.name.as("hotelName"),
                h.address.as("address"))).from(c).leftJoin(h).on(c.id.eq(h.city)).fetchResults().getResults();
        return results1;
    }

1.2、方式二

这种方式是可以的

    /**
     * 方式二 fields 投影
     * todo 调试成功
     * @return
     */
    @Override
    public List<CityHotelVo2> projectionsFields() {
        JPAQuery<CityHotelVo> query = new JPAQuery<>(em);
        QTCity c = QTCity.tCity;
        QTHotel h = QTHotel.tHotel;

        JPAQuery<CityHotelVo2> on = query.select(
                Projections.fields(CityHotelVo2.class,
                        c.id,
                        c.name,
                        h.address))
                .from(c).leftJoin(h).on(c.id.eq(h.city));
        List<CityHotelVo2> resultList = on.createQuery().getResultList();
        return resultList;
    }

1.3、方式三

 /**
     * todo 成功测试
     *  经测试，使用构造器方式可以映射
     * @return
     */
    @Override
    public List<CityHotelVo2> findcityHotel_31() {
        QTCity c = QTCity.tCity;
        QTHotel h = QTHotel.tHotel;
        JPAQueryFactory queryFactory = new JPAQueryFactory(em);

        JPAQuery<CityHotelVo2> on = queryFactory.select(
                Projections.constructor(CityHotelVo2.class,
                        c.id,
                        c.name,
                        h.address))
                .from(c).leftJoin(h).on(c.id.eq(h.city));
        List<CityHotelVo2> results = on.fetchResults().getResults();
        return results;
    }

注意这种构造器方式，只支持对数值和String类型的映射处理，当你定义了Date等等类型，需要在构造函数中，构造如下

@Data
@Accessors(chain = true)
public class CityHotelVo4 implements Serializable {
    private static final long serialVersionUID = 2546523L;
    private Integer id;
    private String cityName;
    private String hotelName;
    private String address;
    
    private LocalDateTime formatTime;
    public CityHotelVo4(Integer id, String cityName, String hotelName, String address, String formatTime) throws ParseException {
        this.id = id;
        this.cityName = cityName;
        this.hotelName = hotelName;
        this.address = address;
        this.formatTime = DateUtils.parseLocalDateTime(formatTime);
    }
}

1.4、总结，这里只是几种尝试，可供参考，可能和QueryDsl版本依赖有关，此处当前测试，版本信息

<properties>
    <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8project.reporting.outputEncoding>
    <java.version>1.8java.version>

    <springboot.start.version>2.0.8springboot.start.version>
    <queryDsl>4.1.4queryDsl>
    <queryslBuild>1.1.3queryslBuild>

properties>

二、接收分页，排序参数

QueryDsl 查询中并不支持前端传参，后映射写入sql 条件（order by ‘字段’ ‘排序规则’），如下

    @Override
    public QueryResults<Tuple> findCityAndHotelPage(Predicate predicate, Pageable pageable) {
        JPAQueryFactory queryFactory = new JPAQueryFactory(em);
        JPAQuery<Tuple> jpaQuery = queryFactory.select(
                QTCity.tCity.id,
                QTHotel.tHotel).from(QTCity.tCity)
                .leftJoin(QTHotel.tHotel)
                .on(QTHotel.tHotel.city.longValue().eq(QTCity.tCity.id.longValue()))
                .where(predicate)
//                .orderBy(new OrderSpecifier<>(Order.DESC,QTCity.tCity.id))
                .orderBy(QTCity.tCity.id.asc()) // 只能这样写死的
                .offset(pageable.getOffset())
                .limit(pageable.getPageSize());
        return jpaQuery.fetchResults();
    }

如何封装，实现以下呢？

.orderBy(pageable.getProperty,pageable.getOrder())

可以这样做

    @Override
    public QueryResults<Tuple> findCityAndHotelPage2(Predicate predicate, Pageable pageable) {
        JPAQueryFactory queryFactory = new JPAQueryFactory(em);
        JPAQuery<Tuple> jpaQuery = queryFactory.select(
                QTCity.tCity.id,
                QTHotel.tHotel).from(QTCity.tCity)
                .leftJoin(QTHotel.tHotel)
                .on(QTHotel.tHotel.city.longValue().eq(QTCity.tCity.id.longValue()))
                .where(predicate)
                .offset(pageable.getOffset())
                .offset(pageable.getOffset())
                .limit(pageable.getPageSize());

        PathBuilder<Entity> entityPath = new PathBuilder<>(Entity.class, "tCity");
        for (Sort.Order order : pageable.getSort()) {
            PathBuilder<Object> path = entityPath.get(order.getProperty());
            jpaQuery.orderBy(new OrderSpecifier(com.querydsl.core.types.Order.valueOf(order.getDirection().name()), path));
        }
        return jpaQuery.fetchResults();
    }

如图

映射SQL为,正常打印

select tcity0_.id       as col_0_0_,
	   thotel1_.id      as col_1_0_,
	   thotel1_.id      as id1_1_,
	   thotel1_.address as address2_1_,
	   thotel1_.city    as city3_1_,
	   thotel1_.name    as name4_1_
from t_city tcity0_
		 left outer join t_hotel thotel1_ on (cast(thotel1_.city as signed) = cast(tcity0_.id as signed))
order by tcity0_.name desc
limit ?

需要注意的是，new PathBuilder<>(Entity.class, “tCity”)，这个起别名的时候是需要注意的，可以先运行测试，再对此调整！！

三、引用Mysql函数

3.1、示例1

    @GetMapping("/s11")
    public ResultBean s11(CityHotelVo vo,
                          @RequestParam(defaultValue = "1") int page,
                          @RequestParam(defaultValue = "3") int rows,
                          @RequestParam(defaultValue = "id") String sidx,
                          @RequestParam(defaultValue = "asc") String sord) {

        Pageable pageable = PageRequest.of(page - 1, rows, "desc".equals(sord) ? Sort.Direction.DESC : Sort.Direction.ASC, sidx);
        BooleanBuilder builder = this.builder1(vo);
        QTCity c = QTCity.tCity;
        
        // 此处引入了内置的 Mysql 函数
        StringTemplate dateExpr = Expressions.stringTemplate("DATE_FORMAT({0},'%Y-%m-%d')", c.cityDateTime);
        builder.and(dateExpr.gt(vo.getStartTime().format(DateTimeFormatter.ofPattern("yyyy-MM-dd"))));
        
        QueryResults<Tuple> results = tCityRepo.findCityAndHotelPage2(builder, pageable);
        List<Tuple> list = results.getResults();
        List<Vo1> collect = list.stream().map(Vo1::new).collect(Collectors.toList());
        return ResultBean.ok(collect);
    }

SQL 映射

select tcity0_.id               as col_0_0_,
	   thotel1_.id              as col_1_0_,
	   thotel1_.id              as id1_1_,
	   thotel1_.address         as address2_1_,
	   thotel1_.city            as city3_1_,
	   thotel1_.hotel_date      as hotel_da4_1_,
	   thotel1_.hotel_date_time as hotel_da5_1_,
	   thotel1_.name            as name6_1_
from t_city tcity0_
		 left outer join t_hotel thotel1_ on (cast(thotel1_.city as signed) = cast(tcity0_.id as signed))
where date_format(tcity0_.city_date_time, '%Y-%m-%d') > ?
order by tcity0_.id desc
limit ?

3.2、示例2

   @Override
    public List<CityHotelVo4> dateFormat(CityHotelVo vo) {
        JPAQueryFactory queryFactory = new JPAQueryFactory(em);
        QTCity c = QTCity.tCity;
        QTHotel h = QTHotel.tHotel;

        StringTemplate dateFormat = Expressions.stringTemplate("DATE_FORMAT({0},'%Y-%m-%d')", c.cityDateTime);

        // 拼接内置函数
        JPAQuery<CityHotelVo4> on = queryFactory.select(
                Projections.constructor(CityHotelVo4.class,
                        // todo 待调试
                        c.id.as("id"),
                        c.name.as("cityName"),
                        h.name.as("hotelName"),
                        h.address,
                        dateFormat.as("formatTime")
                )
        )
                .from(c).leftJoin(h).on(c.id.eq(h.city));
        List<CityHotelVo4> results = on.fetchResults().getResults();
        return results;
    }

SQL 映射

select tcity0_.id                                      as col_0_0_,
	   tcity0_.name                                    as col_1_0_,
	   thotel1_.name                                   as col_2_0_,
	   thotel1_.address                                as col_3_0_,
	   date_format(tcity0_.city_date_time, '%Y-%m-%d') as col_4_0_
from t_city tcity0_
	left outer join t_hotel thotel1_ on (tcity0_.id = thotel1_.city)

3.3、示例3

3.4、示例4

四、其他