将特定查询转换为 JPQL 或 Criteria Builder 查询

Question

这是 2 个实体的代码（它在数据库中生成三个表）。 Book 实体：

@Entity
public class Book {
    @Id
    private long id;

    private String name;

    @ManyToMany
    private List<Author> authors;
}

Author 实体：

@Entity
public class Author {
    @Id
    private long id;

    @Column(unique=true)
    private String name;
}

我正在尝试按作者列表查找书籍。这是一个sql查询：

select book.id, ARRAY_AGG(author.name)
from book 
join book_authors ba on book.id=ba.book_id 
join author on ba.authors_id=author.id
group by book.id
having  ARRAY_AGG(distinct author.name order by author.name)=ARRAY['a1', 'a2']::varchar[]

['a1', 'a2'] 是书籍作者列表，必须作为参数传递。这个想法是聚合作者，然后将它们与传递的参数列表进行比较。

如何将此 SQL 查询重写为 JPQL 或 CriteriaBuilder 查询？

Answer 1

@Query("select distinct b from Book b join b.authors a where a.name in(:names)")
List<Book> findByAuthorsNames(@Param("names") List<String> names)

如果你想获取b.authors 使用join fetch 而不是join

Answer 2

如果需要完全匹配，您可以像这样使用Specification

public class BookSpecifications {
        public static Specification<Book> byAuthorsNames(List<String> names) {
            return (root, query, builder) -> {
                Join<Book, Author> author = root.join("authors", JoinType.LEFT);

                Predicate predicate = builder.conjunction;
                for(String name : names) {
                    Predicate namePredicate = builder.and(author.get("name"), name);
                    predicate = builder.and(predicate, namePredicate);
                }

                return predicate;
            }
        }
}

BookRepository 必须扩展 JpaSpecificationExecutor。

用法：

BookRepository repository;

public List<Book> findByAuthorsNames(List<String> names) {
    return repository.findAll(BookSpecifications.byAuthorsNames(names));
}