这不是经典的N + 1问题。我的问题是在Jpa中使用投影和DTO对象。
我有JPA Query的下一个方法：
public List<MeterDTO> getAllBrokenMeterByHouseServ(House house, Serv serv, Date dt) {
Query query =em.createQuery("select new MeterDTO(m, g.kart.lsk, nvl(e.tp,0)) from Meter m "
+ "join m.exs e with m.id=e.meter.id "
+ "join m.meterLog g with m.meterLog.id=g.id "
+ "join g.kart k with g.kart.id=k.id and :dt between k.dt1 and k.dt2 "
+ "join g.serv s with g.serv.id=s.id "
+ "join k.kw kw with k.kw.id=kw.id "
+ "join kw.house h with kw.house.id=h.id "
+ "where s.id = :servId "
+ "and kw.house.id = :houseId "
+ "and :dt between e.dt1 and e.dt2 and nvl(e.tp,0) in (2,3,4) "
+ "");
query.setParameter("servId", serv.getId());
query.setParameter("houseId", house.getId());
query.setParameter("dt", dt);
return query.getResultList();
}
我从上面的查询中获取记录到 数据传输对象：
meterDao.getAllBrokenMeterByHouseServ(house, serv, dt2).stream().forEach(t-> {
log.info("meter.id={}, lsk={}, tp={} ", t.getMeter().getId(), t.getLsk(), t.getTp());
});
MeterDTO：
@Getter @Setter
public class MeterDTO {
private Meter meter;
private Integer lsk;
private Double tp;
public MeterDTO(Meter meter, Integer lsk, Double tp) {
super();
this.meter = meter;
this.lsk = lsk;
this.tp = tp;
}
}
为什么hibernate会产生一个主要查询：
select
meter0_.ID as col_0_0_,
kart3_.lsk as col_1_0_,
nvl(exs1_.TP,
0) as col_2_0_
from
MT.METER meter0_
inner join
MT.METER_EXS exs1_
on meter0_.ID=exs1_.FK_METER
and (
meter0_.ID=exs1_.FK_METER
)
inner join
MT.METER_LOG meterlog2_
on meter0_.FK_METER_LOG=meterlog2_.ID
and (
meter0_.FK_METER_LOG=meterlog2_.ID
)
inner join
AR.KART kart3_
on meterlog2_.FK_KLSK_OBJ=kart3_.FK_KLSK_OBJ
and (
kart3_.lsk=kart3_.lsk
and (
? between kart3_.DT1 and kart3_.DT2
)
)
inner join
AR.KW kw6_
on kart3_.FK_KW=kw6_.ID
and (
kart3_.FK_KW=kw6_.ID
)
inner join
AR.HOUSE house7_
on kw6_.FK_HOUSE=house7_.ID
and (
kw6_.FK_HOUSE=house7_.ID
)
inner join
TR.SERV serv5_
on meterlog2_.FK_SERV=serv5_.ID
and (
meterlog2_.FK_SERV=serv5_.ID
)
where
serv5_.ID=?
and kw6_.FK_HOUSE=?
and (
? between exs1_.DT1 and exs1_.DT2
)
and (
nvl(exs1_.TP, 0) in (
2 , 3 , 4
)
)
和具有不同绑定参数的多个查询“？”加载每个实体：
select
meter0_.ID as ID1_44_0_,
meter0_.FK_K_LSK as FK_K_LSK2_44_0_,
meter0_.FK_METER_LOG as FK_METER_LOG4_44_0_,
meter0_.TRANS_RATIO as TRANS_RATIO3_44_0_
from
MT.METER meter0_
where
meter0_.ID=?
如何避免此问题？我想在一个主查询中加载所有实体Meter。 有可能吗？
我用：
<spring-framework.version>5.0.5.RELEASE</spring-framework.version>
<hibernate.version>5.1.0.Final</hibernate.version>
非常感谢任何帮助。
upd1
我将我的JPA查询代码简化为：
public List<MeterDTO> getAllBrokenMeterByHouseServ(House house, Serv serv, Date dt) {
Query query =em.createQuery("select new com.ric.bill.dto.MeterDTO(m) from Meter m ");
}
但它仍会产生多个查询：
select
meter0_.ID as ID1_44_0_,
meter0_.FK_K_LSK as FK_K_LSK2_44_0_,
meter0_.FK_METER_LOG as FK_METER_LOG4_44_0_,
meter0_.TRANS_RATIO as TRANS_RATIO3_44_0_
from
MT.METER meter0_
where
meter0_.ID=?
20-04-2018 12:52:49.482 [main] DEBUG o.h.l.p.e.p.i.ResultSetProcessorImpl - Starting ResultSet row #0
20-04-2018 12:52:49.482 [main] DEBUG org.hibernate.SQL -
select
meter0_.ID as ID1_44_0_,
meter0_.FK_K_LSK as FK_K_LSK2_44_0_,
meter0_.FK_METER_LOG as FK_METER_LOG4_44_0_,
meter0_.TRANS_RATIO as TRANS_RATIO3_44_0_
from
MT.METER meter0_
where
meter0_.ID=?
<Skipped>
upd2 Meter实体：
@SuppressWarnings("serial")
@Entity
@Table(name = "METER", schema="MT")
@Getter @Setter
public class Meter extends Base implements java.io.Serializable, Storable {
public Meter (){
}
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
@Column(name = "ID", updatable = false, nullable = false)
protected Integer id;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="FK_METER_LOG", referencedColumnName="ID")
private MeterLog meterLog ;
@OneToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval=true)
@JoinColumn(name="FK_METER", referencedColumnName="ID")
@BatchSize(size = 50)
private List<Vol> vol = new ArrayList<Vol>(0);
@OneToMany(fetch = FetchType.LAZY)
@JoinColumn(name="FK_METER", referencedColumnName="ID")
@BatchSize(size = 50)
private List<MeterExs> exs = new ArrayList<MeterExs>(0);
@Column(name = "TRANS_RATIO", updatable = true, nullable = true)
private Double trRatio;
}
答案 0 :(得分：1)
在DTO中，您有“仪表”和“仪表”。字段，在米字段中你有＆＃39; MeterLog仪表日志＆＃39;在这种情况下，Hibernate还为整个对象加载字段。这个DTO要复杂得多。尝试创建更多扁平对象：
var fs = require('fs');
var x =
{
"members": {
"Thing": {
"someValue": "1",
"anotherValue": "2"
},
"secondThing":{
"secondValue":"3",
"anotherSecondVal":"4"
}
}
}
fs.writeFile('members.json', JSON.stringify(x), 'utf8', (err,data)=>{
//callback
});
fs.readFile('members.json','utf8',(err,data)=>{
if(data){
console.log(JSON.parse(data))
} else{
console.log(err)
}
})查询将是：
public class MeterDTO {
private Integer meterId
private Double meterTrRatio
private Integer lsk;
private Double tp;
(...)
之后，您可以将DTO扩展到您想要的下一个字段。
答案 1 :(得分：0)
接受的答案建议更改 DTO，这并不总是可接受的解决方案。
这是一个无需更改 DTO 的解决方案。
像这样编写您的 HQL：
from Meter m
join m.exs e with m.id=e.meter.id
join m.meterLog g with m.meterLog.id=g.id
join g.kart k with g.kart.id=k.id and :dt between k.dt1 and k.dt2 "
join g.serv s with g.serv.id=s.id "
join k.kw kw with k.kw.id=kw.id "
join kw.house h with kw.house.id=h.id "
(more joins and wheres)
请注意，不应有任何 select。
getResultList 会给你 List<Object[]>。每个条目都是一个 {Meter, m.exs, m.meterLog, g.kart, ....} 数组。选择您需要的并制作您的 MeterDTO。
就我而言：
jpa 仓库
@Query("from Bind bind "
+ "left join Employee employee "
+ "with bind.empCode = employee.empCode "
+ "where bind.accountName = :hiveAccount and bind.disabled = 1 ")
List<Object[]> listMembers(@Param("hiveAccount") String hiveAccount);
DTO
public class BindDTO {
Bind bind;
Employee emp;
public BindDTO(Object[] objs) {
this((Bind) objs[0], (Employee) objs[1]);
}
服务
myRepo.listMembers(hiveAccount).stream().map(BindDTO::new).collect(Collectors.toList());