After successfully adding child entity with parent reference, child does not show under parent resource

问题

I have two entities, Shelf and Book. A Shelf can have multiple Books (the relationship is bi-directional). I've exposed both of these as JpaRepositories.

Here's the issue:

I create a shelf by posting { "name":"sci-fi" } to /shelves.(success)
I create a book for that shelf by posting { "name":"mybook", "shelf":"localhost:8080/shelves/1" } to /books. (success)
When I get the book I just created at /books/1, it has the correct link to the parent shelf.
But when I go to shelves/1/books, I get an empty result, { }!

Any ideas what I might be missing?

Right now I've constructed a workaround by explicitly adding the book to its shelf in a beforeCreate event, but it seems like this should be totally unnecessary. (It does fix the problem, however.)

@HandleBeforeCreate(Book.class)
public void handleCreate(Book book) {
  // why is this necessary?
  book.getShelf().getBooks().add(book); 
}

Here are the entity classes:

@Entity
public class Book {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    private String name;

    @ManyToOne
    private Shelf shelf;

    public Shelf getShelf() {
    return shelf;
    }

    public void setShelf(Shelf shelf) {
    this.shelf = shelf;
    }

    public String getName() {
    return name;
    }

    public void setName(String name) {
    this.name = name;
    }

    @Override
    public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
    }

    @Override
    public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Book other = (Book) obj;
    if (name == null) {
        if (other.name != null)
        return false;
    } else if (!name.equals(other.name))
        return false;
    return true;
    }
}

@Entity
public class Shelf {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private long id;

    private String name;

    @OneToMany
    private List<Book> books = new ArrayList<Book>();

    public List<Book> getBooks() {
    return books;
    }

    public void setBooks(List<Book> books) {
    this.books = books;
    }

    public String getName() {
    return name;
    }

    public void setName(String name) {
    this.name = name;
    }

    @Override
    public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((name == null) ? 0 : name.hashCode());
    return result;
    }

    @Override
    public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    Shelf other = (Shelf) obj;
    if (name == null) {
        if (other.name != null)
        return false;
    } else if (!name.equals(other.name))
        return false;
    return true;
    }

}

I'm using Spring Boot 1.1.8.

回答1:

In your Shelf entity, add the mappedBy = "self" property to the @OneToMany annotation in books:

@OneToMany(mappedBy = "self")
private List<Book> books = new ArrayList<Book>();

This will auto populate the list of books with the books whose reference to self matches.

回答2:

I think you need to update shelf to add new book you created as a last step. This is because you are using bi-directional relationship and shelf has no idea about books till you update it with the books it should hold.

来源：https://stackoverflow.com/questions/26805228/after-successfully-adding-child-entity-with-parent-reference-child-does-not-sho

标签

spring-data-rest