Spring Boot getting empty _embedded array for related entity - spring

Question

Using Spring Boot I'm Having the following abbreviated structure of entities:
#Entity
#Table(name = "item")
#Inheritance(strategy = InheritanceType.JOINED)
public abstract class Item implements Serializable {
#Id
#GeneratedValue(strategy = GenerationType.AUTO)
#Column(name = "id", updatable = false)
protected Long id;
...
}
#Entity
#Table(name = "book")
public class Book extends Item implements Serializable {
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name = "item_author", joinColumns = #JoinColumn(name = "item_id", referencedColumnName = "id"), inverseJoinColumns = #JoinColumn(name = "author_id", referencedColumnName = "id"))
private Set<Author> authors;
}
#Entity
#Table(name = "author")
public class Author implements Serializable {
#Id
#GeneratedValue
private Long id;
#ManyToMany(mappedBy="authors")
private List<Book> books = new ArrayList<Book>();
private String name;
}
My DAOs are just plain simple RestResource interfaces for all entities, like:
#RestResource(path="items", rel="items")
public interface ItemDao extends CrudRepository<Item, Long> {
}
When I query an entity by id, it is all good
GET > http://localhost:8080/shelfventory/authors/1
{
"name" : "Jhonny Cash",
"used" : true,
"_links" : {
"self" : {
"href" : "http://localhost:8080/shelfventory/authors/1"
},
"author" : {
"href" : "http://localhost:8080/shelfventory/authors/1"
},
"books" : {
"href" : "http://localhost:8080/shelfventory/authors/1/books"
}
}
}
But when I try to follow the links for a related object I just get an empty embedded:
GET > http://localhost:8080/shelfventory/authors/1/books
{
"_embedded" : {
"books" : [ ]
},
"_links" : {
"self" : {
"href" : "http://localhost:8080/shelfventory/authors/1/books"
}
}
}
What am I doing wrong, how to solve it?

Answer 1

Consider adding these two properties to your application.properties to keep your #Entity and schema in sync:
spring.jpa.generate-ddl=true
spring.jpa.hibernate.ddl-auto=true