Hibernate #Query throw syntax error at or near "." - spring-data-jpa

Question

I try to get field tags from the entity Article:
#Getter
#Setter
#Entity
#ToString
#NoArgsConstructor
#AllArgsConstructor
#Table(name = "articles")
public class Article {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Embedded
private Author author;
#Column(unique = true)
private String title;
private String content;
#ElementCollection(targetClass = String.class,
fetch = FetchType.EAGER
)
#CollectionTable(name = "tags",
joinColumns = #JoinColumn(name = "article_id")
)
#Column(name = "tag")
private List<String> tags = new ArrayList<>();
}
With ArticleRepository extends JpaRepository<Article, Long>, JpaSpecificationExecutor<Article> and #Query:
#Query("SELECT " +
" new java.util.ArrayList(a.tags) " +
" FROM Article a " +
" WHERE a.title = :title")
List<String> findAllTagsOfArticle(String title);
And get a result:
Hibernate:
select
. as col_0_0_
from
articles article0_
inner join
tags tags1_
on article0_.id=tags1_.article_id
where
article0_.title=?
2022-07-21 15:17:24.666 WARN 2196 --- [ scheduling-1] o.h.engine.jdbc.spi.SqlExceptionHelper : SQL Error: 0, SQLState: 42601
2022-07-21 15:17:24.666 ERROR 2196 --- [ scheduling-1] o.h.engine.jdbc.spi.SqlExceptionHelper : ERROR: syntax error at or near "."
Generated SQL query looks correct but after SELECT hibernate generate .
Why does it happens and how to fix it?

Answer 1

You cannot pass a collection (a.tags) like that. The idea is that the constructor will receive a single row from the query result.
But also, there's no need to use new ArrayList.
This should work:
#Query("select t from Article a join a.tags t where a.title = :title")
List<String> findAllTagsOfArticle(String title);
You can also simplify a bit the mapping:
#ElementCollection
#CollectionTable(name = "tags",
joinColumns = #JoinColumn(name = "article_id")
)
#Column(name = "tag")
private List<String> tags = new ArrayList<>();
There is no need to specify EAGER and the target class in this case.