SemanticException：使用 JPQL 子选择时，选择列表中位置 1 处的选择项没有别名

Question

给定实体：

@Entity
@Data
public class Collection {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  private String createdBy;

  @OneToMany(mappedBy = "collection")
  private List<CollectionAccess> collectionAccesses;

}

@Entity
@Data
public class CollectionAccess {

  @Id
  @GeneratedValue(strategy = GenerationType.IDENTITY)
  private Long id;

  @ManyToOne
  @JoinColumn(
      foreignKey =
          @ForeignKey(
              value = ConstraintMode.PROVIDER_DEFAULT,
              name = "fk_collectionaccess_collection_collections_id"))
  private Collection collection;

  private Integer accessType;
  private LocalDateTime expirationAtUtc;
}

给定数据库：

select id, created_by from collection;
+----+------------+
| id | created_by |
+----+------------+
| 40 |   ABC123   |
+----+------------+

select * from collection_access;
+----+-------------+----------------------------+---------------+
| id | access_type | expiration_at_utc          | collection_id |
+----+-------------+----------------------------+---------------+
|  2 |           0 | 2011-12-03 03:15:30.000000 |            40 |
|  3 |           1 | 2011-12-03 03:15:30.000000 |            40 |
+----+-------------+----------------------------+---------------+

编写此查询会导致 SemanticException：

em.createQuery(
          "SELECT t FROM (SELECT c FROM Collection c "
                  + "LEFT JOIN c.collectionAccesses ca WHERE c.id = ?1 "
                  + "AND (c.createdBy = ?2 OR (ca.accessType = ?3 AND ca.expirationAtUtc <= ?4))) t "
                  + "JOIN FETCH t.collectionAccesses ",
          Collection.class)
      .setParameter(1, id)
      .setParameter(2, "ABC123")
      .setParameter(3, 1)
      .setParameter(4, now)
      getSingleResult();


java.lang.IllegalArgumentException: org.hibernate.query.SemanticException: Select item at position 1 in select list has no alias (aliases are required in CTEs and in subqueries occurring in from clause)
    at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:143) ~[hibernate-core-6.4.4.Final.jar:6.4.4.Final]

如何在 JPQL/Hibernate 中正确编写

SELECT

查询

FROM

a

subselect

？

Answer 1

JPQL 中的 FROM 子句中不能使用子查询。您有 2 个选择：

1. 使用本机查询

2. 尝试重写查询以替换 FROM 子句中的子查询 但是，在分析您的查询后，我不太明白为什么您需要该子选择。 我认为这样做就可以了：

   em.createQuery( “从集合 c 中选择 c” +“JOIN FETCH c.collectionAccesses ca WHERE c.id = ?1” + "AND (c.createdBy = ?2 OR (ca.accessType = ?3 AND ca.expirationAtUtc <= ?4)), Collection.class) .setParameter(1, id) .setParameter(2, "ABC123") .setParameter(3, 1) .setParameter(4, now) getSingleResult();

如果我的建议没有达到您的目标，如果您解释一下您需要什么结果，将会有所帮助。