Spring Data JPA Property Expressions for a many to many query

Question

I'm using Spring boot 2, with Spring data & Spring Data JPA, and I'm looking to replace some existing @Query methods with Spring Data JPA's Property Expressions

However I'm struggling to workout the expression name for a many to many relationship. I'm not too sure if this is possible, as all the example I've seen are based on a one-to-many relationship.

A basic example could be:

Book Entity

@Entity
@Table(name = "book")
public class Book {

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

    @Column(name = "title")
    private String title;

    @ManyToMany(mappedBy = "authors", cascade = CascadeType.REFRESH, fetch = FetchType.LAZY)
    private Set<Author> authors = new HashSet<>();

    // Getter and Setters
}

Author Entity

@Entity
@Table(name = "Author")
public class Author {

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

    @Column(name = "forename")
    private String firstName;

    @Column(name = "surname")
    private String surname;

    @ManyToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
    @JoinTable(
        name = "author_books",
        joinColumns = @JoinColumn(name = "author_id", referencedColumnName = "id"),
        inverseJoinColumns = @JoinColumn(name = "book_id", referencedColumnName = "id"),
        uniqueConstraints = @UniqueConstraint(columnNames = {"author_id", "book_id"})
    )
    private Set<Book> books = new HashSet<>();

    // Getter and Setters
}

The current SQL query looks something like this:

SELECT *
FROM book
LEFT JOIN author_books ON author_books.book_id = book.id
WHERE author_books.author_id = 1;

How would you write the equivalent Spring JPA Property Expressions (if possible) within a Book repository?

I've tried the following (with no luck):

List<Book> findByBooks_AuthorId(Long authorId);
List<Book> findByBooks_Author_Id(Long authorId);
List<Book> findByBooks_AuthorsId(Long authorId);
List<Book> findByBooks_Authors_Id(Long authorId);

One solution would be to obtain the author object by it's id, and then calling author.getBooks() . However, I would like to be able to provide filtering and pagination of results using the spring data PageRequest and Specification classes.

Any help would be really appreciated.

Answer 1

What you need is to find books by author's ID. So you need to write it as the method's name:

List<Book> findByAuthorsId(Long id);

That's it! Also it is unnecessary to use @Column (name=...) annotation if the target column's name is the same as entity field's name. Property expressions

Answer 2

have you tried using Query Annotation.. https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.query-methods.at-query

@Query("SELECT * FROM book LEFT JOIN author_books ON author_books.book_id = book.id WHERE author_books.author_id = ?1")
List<Book> findByBooks_AuthorId(Long authorId);

Answer 3

您可以尝试以下方法：

List<Book> findAllByAuthorId(Author author);