Question

我有三节课：

BookController.java

@Controller
public class BookController {

@Autowired
private BookRepository book_repository;

@Autowired
private CategoryRepository category_repository;

@Autowired
private BookServiceImpl bookServiceImpl;

@RequestMapping(value = "/booklist")
public String bookList(Model model) {
    model.addAttribute("books", book_repository.findAll());
    return "booklist";
}

@RequestMapping(value = "/findbycategory")
public List<Book> findBookByCategory()..... (need to implement)

}

Book.java

@Entity
public class Book {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long id;
private String title;
private String author;
private int year = 1600;
private String isbn;
private double price;

@ManyToOne
@JsonIgnore
@JoinColumn(name = "categoryId")
private Category category;

setters/getters/constructors...
}

Category.java

@Entity
public class Category {

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
private Long categoryId;
private String categoryName;

@OneToMany(cascade = CascadeType.ALL, mappedBy = "category")
private List<Book> books;
...
}

BookRepository.java

@RepositoryRestResource
public interface BookRepository extends CrudRepository<Book, Long> {

List<Book> findByAuthor(@Param("author") String author);

List<Book> findByTitleLike(String title);
}

我想编写一个findBooksByCategory（）方法，该方法按类别返回所有书籍。我在Category和Book之间有OneToMany关系。类别是作为单独的实体。我会知道如何通过说id（来自Book.java）来查找书，但是当我们将类字段作为其他对象的实例时，我不知道如何表现。

Answer 1

看看Property Expressions

有多种方法可以实现您要实现的目标。可能的一种是；

List<Book> findAllByCategory(Category category);

由@Compass建议

如果您想更具体一些，例如通过类别名称，您可以；

List<Book> findAllByCategoryCategoryName(String categoryName);

或

List<Book> findAllByCategory_CategoryName(String categoryName);

然后有一种本机的方法[假设表名和列];

@Query(value="select b.* from book b inner join category c on b.category = c.id where c.name = ?1", nativeQuery=true)
List<Book> customQueryToFindListOfBooks(String categoryName);

如何按类别查找书籍？

1 个答案: