[英]JPA CriteriaBuilder Subquery multiselect
我有一个关于 jpa 中的子查询类的问题。 我需要用两个自定义字段创建子查询,但子查询没有多选方法,选择方法有表达式输入参数(在查询中这是选择)和不适合的 constact 方法。
另外我对加入子查询结果有疑问,这可能吗? 以及怎么做?
我有:
链实体
public class Chain {
@Id
@Column(name = "chain_id")
@GeneratedValue(generator = "seq_cha_id", strategy = GenerationType.SEQUENCE)
@SequenceGenerator(name = "seq_cha_id", sequenceName = "SEQ_CHA_ID", allocationSize = 1)
private Long id;
@Column(name = "user_id")
private Long userId;
@Column(name = "operator_id")
private Long operatorId;
@Column(name = "subject")
private String subject;
@OneToMany(fetch = FetchType.LAZY, mappedBy = "chain")
private List<Message> messages;
@Column(name = "status")
private Status status;
public Long getOperatorId() {
return operatorId;
}
public void setOperatorId(Long operatorId) {
this.operatorId = operatorId;
}
public Status getStatus() {
return status;
}
public void setStatus(Status status) {
this.status = status;
}
public Long getUserId() {
return userId;
}
public void setUserId(Long userId) {
this.userId = userId;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getSubject() {
return subject;
}
public void setSubject(String theme) {
this.subject = theme;
}
public List<Message> getMessages() {
return messages;
}
public void setMessages(List<Message> messages) {
this.messages = messages;
}
}
消息实体
public class Message {
@Id
@Column(name = "message_id")
@GeneratedValue(generator = "seq_mess_id", strategy = GenerationType.SEQUENCE)
@SequenceGenerator(name = "seq_mess_id", sequenceName = "SEQ_MESS_ID", allocationSize = 1)
private Long id;
@Column(name = "user_id")
private Long userId;
@Column(name = "message", nullable = true, length = 4000)
private String message;
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "chain_id")
private Chain chain;
@Column(name = "creation_date")
private Date date;
@Column(name = "status")
private Status status;
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public Long getUserId() {
return userId;
}
public void setUserId(Long userId) {
this.userId = userId;
}
public String getMessage() {
return message;
}
public void setMessage(String message) {
this.message = message;
}
public Chain getChain() {
return chain;
}
public void setChain(Chain chain) {
this.chain = chain;
}
public Date getDate() {
return date;
}
public void setDate(Date date) {
this.date = date;
}
public Status getStatus() {
return status;
}
public void setStatus(Status status) {
this.status = status;
}
}
用于查询的包装器
public class MessageWrapper {
private final Long chainId;
private final Long messageId;
public MessageWrapper(Long chainId, Long messageId) {
this.chainId = chainId;
this.messageId = messageId;
}
}
我需要创建这个查询(这是查询的一部分,我从谓词中得到的另一部分。JPQL 不合适)
SELECT ch.*
FROM hl_chain ch,
(SELECT mes.chain_id,
max(message_id) message_id
FROM hl_message mes
GROUP BY chain_id) mes
WHERE mes.chain_id = ch.chain_id
ORDER BY message_id;
在子查询中我做
Subquery<MessageWrapper> subquery = criteriaQuery.subquery(MessageWrapper.class);
Root<Message> subRoot = subquery.from(Message.class);
subquery.select(cb.construct(
MessageWrapper.class,
subRoot.get(Message_.chain),
cb.max(subRoot.get(Message_.id))
));
但是,子查询在参数中没有使用 CompoundSelection 进行选择,并且我无法使用CriteriaBuilder
构造方法。
映射为实体的数据库视图将完成您需要的工作。 它被映射为一个普通的表,只用标签@View 代替。
我在我的项目中也做了同样的事情。
您可以从 JPA 调用本机查询,例如:
Query q = em.createNativeQuery("SELECT p.firstname, p.lastname FROM Person p");
List<Object[]> persons= q.getResultList();
for (Object[] p : persons) {
System.out.println("Person "
+ p[0]
+ " "
+ p[1]);
}
CriteriaBuilder cb = session.getCriteriaBuilder();
CriteriaQuery<MessageWrapper> q = cb.createQuery(MessageWrapper.class);
Root<Chain> c = q.from(Chain.class);
Join<Chain, Message> m = p.join("messages");
q.groupBy(c.get("id"));
q.select(cb.construct(MessageWrapper.class, c.get("id"), cb.max(m.get("id"))));
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