JPA：與堅持外鍵約束

Question

我有問題二實體：

客戶實體

@Entity 
public class Customer { 

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

private String name; 

@OneToMany(mappedBy="customer", cascade=CascadeType.ALL) 
private List<Facility> facilities; 

//Setter and Getter for name and facilities 

public void addFacility(Facility facility){ 
    this.facilities.add(facility); 
} 
} 

設施實體

@Entity 
public class Facility { 

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

@ManyToOne 
@JoinColumn(name="CUSTOMER_FK") 
private Customer customer; 

private String name; 

//Setter and Getter, equals and hashcode 
... 
} 

因此，在我主我這樣做

Customer customer = new Customer(); 
    customer.setName("Wake Forest University"); 
    Facility facility = new Facility(); 
    facility.setName("Tom Cruise"); 
    EntityManager entityManager = Persistence.createEntityManagerFactory("EntityClassPU").createEntityManager(); 
    entityManager.getTransaction().begin(); 
    customer.addFacility(facility); 
    entityManager.persist(customer); 
    entityManager.getTransaction().commit(); 

Wake Forest University被成功插入到Customer,Tom Cruise被成功插入Facility，然而在Facility裏，CUSTOMER_FK的值爲空，這表明我失敗了持續的外鍵約束。我在這裏做錯了什麼？

Answer 1

您與Customer和Facility之間的關係是雙向關聯，您需要必須管理關聯的兩端。你可以手動做到這一點，但我建議在addFacility()方法中做：

public void addFacility(Facility facility){ 
    if (this.facilities == null) { 
     this.facilities = new ArrayList<Facility>(); 
    } 
    this.facilities.add(facility); 
    facility.setCustomer(this); // that's the part you're currently missing 
}