我正在为我的Web应用程序构建一个消息传递系统,使用Spring MVC,Spring Data JPA和Hibernate作为我的JPA提供者。
我有五个实体:Thread
,ThreadParticipant
,Participant
,Account
和Company
。每个消息线程至少有两个参与者,其中一个与用户(Account
实体)相关联,另一个与Company
相关联。此约束由应用程序强制执行。数据库的设计与此类似,以支持将来的功能。数据库中给定线程的两个参与者的示例如下所示:
id account_id company_id
1 44 NULL
2 NULL 123
id = 1的行是用户,id = 2的行是公司。我想要做的是编写一个HQL查询,该查询提取给定帐户的所有Thread
个对象,包含用户/帐户参与者以及公司参与者。我试图为我的联接使用不同的别名,如下所示:
select distinct t
from Thread t
inner join fetch t.threadParticipants user_tp
inner join fetch t.threadParticipants company_tp
inner join fetch user_tp.participant user_p
inner join fetch user_p.account a
inner join fetch company_tp.participant receiver_p
inner join fetch receiver_p.company
where a.id = :accountId
由于两次cannot simultaneously fetch multiple bags
次提取,我收到异常t.threadParticipants
。如果我在这里只进行一次连接,生成的SQL只会忽略我的额外连接,只会加入Participant
一次,这需要参与者同时拥有一个帐户和一个公司。使用原始SQL,我可以这样做,并且它工作正常:
select *
from thread t
inner join thread_participant user_tp on (user_tp.thread_id = t.id)
inner join thread_participant company_tp on (company_tp.thread_id = t.id)
inner join participant user_p on (user_p.id = user_tp.participant_id)
inner join account a on (a.id = user_p.account_id)
inner join participant company_p on (company_p.id = company_tp.participant_id)
inner join company c on (c.id = company_p.company_id)
where a.id = 123;
如果我没有为同一个表使用不同的别名(请参阅下面的查询),则查询运行正常,但我只返回一个返回的线程参与者 - 与该帐户关联的一个。 / p>
select distinct t
from Thread t
inner join fetch t.threadParticipants tp
inner join fetch tp.participant p
inner join fetch p.account a
left join fetch p.company
where a.id = :accountId
我有什么方法可以做我想用HQL做的事情,还是我必须使用原生SQL?
我的映射如下:
线程实体
@Entity
@Table(name = "thread")
public class Thread {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column
private int id;
@OneToMany(fetch = FetchType.LAZY, mappedBy = "thread", cascade = { CascadeType.PERSIST, CascadeType.MERGE })
private Collection<ThreadParticipant> threadParticipants = new HashSet<>();
// Getters and setters
}
参与实体
@Entity
@Table(name = "participant")
public class Participant {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column
private int id;
@ManyToOne(fetch = FetchType.LAZY, optional = true, targetEntity = Account.class, cascade = { CascadeType.PERSIST })
@JoinColumn(name = "account_id")
private Account account;
@ManyToOne(fetch = FetchType.LAZY, optional = true, targetEntity = Company.class)
@JoinColumn(name = "company_id")
private Company company;
// Getters and setters
}
ThreadParticipant实体
@Entity
@Table(name = "thread_participant")
@IdClass(ThreadParticipantPK.class)
public class ThreadParticipant implements Serializable {
@Id
@ManyToOne(fetch = FetchType.LAZY, targetEntity = Participant.class, cascade = { CascadeType.PERSIST, CascadeType.MERGE })
@JoinColumn(name = "participant_id")
private Participant participant;
@Id
@ManyToOne(fetch = FetchType.LAZY, targetEntity = Thread.class)
@JoinColumn(name = "thread_id")
private Thread thread;
@Column(name = "last_viewed", nullable = true)
private Date lastViewed;
// Getters and setters
}
ThreadParticipantPK
public class ThreadParticipantPK implements Serializable {
private Thread thread;
private Participant participant;
public ThreadParticipantPK() { }
public ThreadParticipantPK(Thread thread, Participant participant) {
this.thread = thread;
this.participant = participant;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (!(o instanceof ThreadParticipantPK)) return false;
ThreadParticipantPK that = (ThreadParticipantPK) o;
if (!participant.equals(that.participant)) return false;
if (!thread.equals(that.thread)) return false;
return true;
}
@Override
public int hashCode() {
int result = thread.hashCode();
result = 31 * result + participant.hashCode();
return result;
}
// Getters and setters
}
提前谢谢!
答案 0 :(得分:2)
尝试将threadParticipants
集合的类型更改为Set
而不是Collection
:
private Set<ThreadParticipant> threadParticipants;