Named Entity Graph Sub-Subgraph

问题

I am new to JPA 2.1 and started using only recently Named Entity Graphs. For my project I am mapping the following relation in JPA 2.1:

Order -> OrderDetail -> Product -> ProductLine

The question:

I want to instruct JPA to join and fetch properly all the needed data. So far this works flawlessly for Order -> OrderDetail -> Product but I have not managed so far to add a Sub-Sub Graph in order to go as deep as the ProductLine class. How do I make a subgraph of a subgraph ? Ex get the ProductLine of the Product ?

Here are my entities (getters and setters omitted):

Order

@Entity
@Table(name="ORDERS")
@NamedEntityGraph(
    name = "graph.Order.details",
    attributeNodes = {
        @NamedAttributeNode(value = "details", subgraph = "graph.OrderDetail.product")
    },
    subgraphs = {
        @NamedSubgraph(name = "graph.OrderDetail.product", attributeNodes = @NamedAttributeNode("product"))
    }
)

public class Order implements Serializable{
  @Id
  @Column(name = "orderNumber")
  private Long number;

  @Column(name = "orderDate")
  private Date date;

  @OneToMany(mappedBy = "order")
  private List<OrderDetail> details;
}

OrderDetail

@Entity
@Table(name = "orderdetails")
public class OrderDetail implements Serializable{

   @ManyToOne(fetch = FetchType.LAZY)
   @JoinColumn(name = "orderNumber")
   @Id
   private Order order;

   @ManyToOne(fetch = FetchType.LAZY)
   @JoinColumn(name = "productCode", nullable = false)
   @Id
   private Product product;

   @Column(name = "orderLineNumber")
   private int lineNumber;

   @Column(name = "quantityOrdered")
   private int quantity;

Product

@Entity
@Table(name = "products")
class Product {
    @Column(name = "productCode")
    @Id
    private String code;

    @Column(name = "quantityInStock")
    public int quantity;

    @ManyToOne
    @JoinColumn(name = "productLine")
    private ProductLine line;

ProductLine

@Entity
@Table(name = "productlines")
public class ProductLine {
    @Id
    @Column(name = "productLine")
    private String line;

    @Column
    private String textDescription;

回答1:

The simple answer is that you cannot do this because, with the current JPA implementation, you would end up doing two separate queries and having to deal with the Cartesian Products. Some future version of JPA could be extended to include more levels of subgraphs, but as it stands today it does not. There is a JPA SPEC group that works on the next version of JPA. Feel free to submit your request/suggestion there.

Here on StockOverflow there is another reference to the same question.

回答2:

You can create multi level entity graphs with dynamic entity graphs. I am using jpa 2.2 and Hibernate 5.3.7 and i am able to create entity graphs and fetch data upto 3 levels . I hope this will work for next level too . Below is the code snippet . For more details and actual code you can checkout my github repo : https://github.com/vaneetkataria/Jpa-Hibernate/blob/master/jdbcToJpaMigration/src/test/java/com/katariasoft/technologies/jpaHibernate/entity/fetch/entitygraph/dynamic/MultiInstructorsDynamicEntityGrpahTests.java

Code snippet :

@SuppressWarnings("unchecked")
    @Test
    @Rollback(false)
    public void fetchInstrctrsIdProofVehiclesStudentsTheirInstructorsVehiclesAndTheirDocuments() {
        doInTransaction(() -> {
            EntityGraph<Instructor> instructorGraph = em.createEntityGraph(Instructor.class);
            instructorGraph.addAttributeNodes(Instructor_.idProof, Instructor_.vehicles);
            Subgraph<Student> studentSubgraph = instructorGraph.addSubgraph(Instructor_.STUDENTS);
            studentSubgraph.addAttributeNodes(Student_.instructors);
            Subgraph<Vehicle> vehicleSubgraph = studentSubgraph.addSubgraph(Student_.VEHICLES);
            vehicleSubgraph.addAttributeNodes(Vehicle_.documents);
            TypedQuery<Instructor> query = em.createQuery("select i from Instructor i ", Instructor.class)
                    .setHint(EntityGraphUtils.FETCH_GRAPH, instructorGraph);
            List<Instructor> instructors = query.getResultList();
            if (Objects.nonNull(instructors))
                instructors.forEach(instructor -> {
                    IdProof idProof = instructor.getIdProof();
                    Set<Vehicle> vehicles = instructor.getVehicles();
                    Set<Student> students = instructor.getStudents();
                    System.out.println(instructor);
                    System.out.println(idProof);
                    if (Objects.nonNull(vehicles))
                        vehicles.forEach(v -> System.out.println(v.getVehicleNumber()));
                    if (Objects.nonNull(students))
                        students.forEach(s -> System.out.println(s.getName()));
                });
        });
    }

来源：https://stackoverflow.com/questions/38505745/named-entity-graph-sub-subgraph