java - Spring Data JPA : query ManyToMany, 按计数选择

Question

我有 2 个实体:书籍和作者。每个都映射到适当的表。我还有第三个表 book_author 因为这两个实体具有多对多关系。我需要从数据库中选择作者数量等于 count 的所有书籍。

书:

    @Entity(name = "Book")
    @Table(name = "book")
    public class Book {
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private int idbook;

        @NotNull
        @Size(max = 100)
        private String bookName;
        private int bookYearWriting;

        @ManyToMany(fetch = FetchType.LAZY,   
            cascade = {
                    CascadeType.PERSIST,        
                    CascadeType.MERGE
            })
        @JoinTable(name = "author_book",
            joinColumns = { @JoinColumn(name = "book_id") },
            inverseJoinColumns  = { @JoinColumn(name = "author_id") }
        )
        private List<Author> authors = new ArrayList<>();
    ...
    }

作者:

    @Entity(name = "Author")
    @Table(name = "author")
    public class Author {
        @Id
        @GeneratedValue(strategy = GenerationType.AUTO)
        private int idauthor;

        @NotNull
        @Size(max = 100)
        private String authorName;

        @ManyToMany(fetch = FetchType.LAZY,  
            cascade = {
                    CascadeType.PERSIST,        
                    CascadeType.MERGE
            },
            mappedBy = "authors")
        private List<Book> books = new ArrayList<>();
    ...
    }

我想要得到类似的东西:

    @Repository
    public interface BookRepository extends PagingAndSortingRepository<Book, Integer> {
         List<Book> findAllByAuthorsCountIs(int count, Pageable pageable);
    }

请告诉我如何获得这个。

Answer 1

您可以在 Hql 查询中使用集合大小。

例如...

从 Book book left 加入 book.authors 其中 book.authors.size == 3

欲了解更多信息，请参阅以下链接...

https://docs.jboss.org/hibernate/core/3.3/reference/en/html/queryhql.html

@Query("从图书中选择图书 book left join book.authors where book.authors.size == ?1") 列表 findAllByAuthorsCountIs(int count, Pageable 可分页);