異常：com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException：列'dog_id'不能爲空

Question

我有兩個具有父子關係的實體。狗明顯是父母，小狗是孩子。我如何堅持小狗和小狗沒有錯誤？

@XmlRootElement(name = "dog") 
@Entity 
@Table(name = "dog", catalog = "zoo") 
public class Dog{ 
    @Id 
   @GeneratedValue(strategy = GenerationType.IDENTITY) 
    private Integer id; 

    @Column(name = "dogname") 
    private String dogName; 

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "Dog") 
    private Set<Puppy> puppies; 

    ...// getters and setters 

    @XmlElementWrapper(name = "puppies") 
    @XmlElement(name = "puppy") 
    public Set<Puppy> getPuppy() { 
     return this.puppies; 
    } 
} 

@Entity 
@Table(name = "puppy", catalog = "zoo") 
public class Puppy{ 
    @Id 
   @GeneratedValue(strategy = GenerationType.IDENTITY) 
    private Integer id; 

    @Column(name = "puppyname") 
    private String puppyName; 

    @ManyToOne(fetch = FetchType.LAZY) 
    @JoinColumn(name = "dog_id", nullable = false) 
    private Dog dog; 

     ...// getters and setters 
} 

基本上，用戶通過狗 - 它是小狗 - 作爲jaxbElement。

@POST 
@Consumes({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON}) 
@Produces({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON}) 
public Response createDog(JAXBElement<Dog> jaxbDog) { 
    Dog dog = jaxbDog.getValue(); 
    dogDao.save(dog); 
    return Response.status(Response.Status.OK).build(); 
} 

我的問題又是如何讓小狗看到母狗的dog_id？

Answer 1

在Dog實體類添加方法爲：

public void addPuppy(Puppy puppy){ 
      if (this.puppies == null){ 
       this.puppies = new HashSet<Puppy>(); 
      } 
      puppy.setDog(this); // <--This will set dog as parent in puppy class 
      this.puppies.add(puppy); 
    } 

添加Cascade作爲ALL爲puppies映射Dog。

當要保存dog與puppy/puppies，你可以寫這樣的：

 Dog dog = ....getDog object/create new dog object 
     Puppy puppy = new Puppy(); 
     // set puppy attributes. 
     dog.addPuppy(puppy); 
     //call save method for dog 
     dogDao.save(dog);