如何坚持一个具有两级oneToMany关系的JPA实体？

Question

我在Spring JPA/Hibernate环境中遇到持久化实体问题。我也使用Lombok插件来减少样板代码。 基本上我有一个实体，称为产品，其具有子产品一对多的关系：

@Entity 
    @Table(name="product") 
    @EqualsAndHashCode(exclude = {"productId"}, callSuper=false) 
    @ToString(includeFieldNames=true, callSuper=true) 
    @Data 
    public class Product implements Serializable { 

     @Id 
     @GeneratedValue(strategy=GenerationType.IDENTITY) 
     @Column(name="product_id") 
     private Integer productId; 


     @OneToMany(fetch = FetchType.EAGER, mappedBy="product" 
      , cascade ={CascadeType.ALL}, orphanRemoval=true) 
     private Set<SubProduct> subProducts; 
    } 

，这是我的子产品，其具有与joinTable另一种一对多的关系称为ProductVariantMap：

@Entity 
@Table(name="sub_product") 
@EqualsAndHashCode(exclude = {"subId","product"}) 
@ToString(includeFieldNames=true, exclude = {"product"}) 
@Data 
public class SubProduct implements Serializable { 

    @Id 
    @GeneratedValue(strategy=GenerationType.IDENTITY) 
    @Column(name="sub_id") 
    private Integer subId; 

    @ManyToOne(fetch = FetchType.LAZY) 
    @JoinColumn(name = "product_id") 
    private Product product; 

    @OneToMany(fetch = FetchType.EAGER, 
     mappedBy="productVariantMapId.subProduct" 
     , cascade = {CascadeType.ALL}) 
    private List<ProductVariantMap> productVariantMaps; 

} 

这是我ProductVariantMap与嵌入式ID包含的productId，SUBID和variantId

@Entity 
@Table(name="product_variant_map") 
@EqualsAndHashCode 
@ToString(includeFieldNames=true) 
@Data 
public class ProductVariantMap implements Serializable { 

    @EmbeddedId 
    private ProductVariantMapId productVariantMapId; 

    @Column(name="variant_value", nullable=false) 
    private String variantValue; 
} 

productVariantMapId：

@Embeddable 
@EqualsAndHashCode(exclude = {"subProduct","product"}) 
@ToString(includeFieldNames=true,exclude = {"subProduct","product"}) 
@Data 
public class ProductVariantMapId implements Serializable { 

    @ManyToOne(fetch = FetchType.EAGER) 
    @JoinColumn(name = "sub_id") 
    private SubProduct subProduct; 

    @ManyToOne(fetch = FetchType.EAGER) 
    @JoinColumn(name = "product_id") 
    private Product product; 

    @ManyToOne(fetch = FetchType.EAGER) 
    @JoinColumn(name = "variant_id") 
    private Variant variant; 


} 

以及最后但并非最不重要的是我的变种：

@Entity 
@Table(name="variant") 
@EqualsAndHashCode(exclude = {"variantId"}) 
@ToString(includeFieldNames=true) 
@Data 
public class Variant implements Serializable { 

    @Id 
    @GeneratedValue(strategy=GenerationType.IDENTITY) 
    @Column(name="variant_id") 
    private Integer variantId; 

    @Column(name="name", nullable=false) 
    private String name; 
} 

我的目标是能够坚持整个关系一气呵成，当我做productRepository.saveAndFlush（产品）。请注意，所有主键都由数据库序列生成器生成，因此它在saveAndFlush之前为空。我有例外下面，当我试图做以上：

java.lang.NullPointerException 
    at org.hibernate.type.descriptor.java.AbstractTypeDescriptor.extractHashCode(AbstractTypeDescriptor.java:65) 
    at org.hibernate.type.AbstractStandardBasicType.getHashCode(AbstractStandardBasicType.java:201) 
    at org.hibernate.type.AbstractStandardBasicType.getHashCode(AbstractStandardBasicType.java:206) 
    at org.hibernate.type.EntityType.getHashCode(EntityType.java:355) 
    at org.hibernate.type.ComponentType.getHashCode(ComponentType.java:241) 
    at org.hibernate.engine.spi.EntityKey.generateHashCode(EntityKey.java:61) 
    at org.hibernate.engine.spi.EntityKey.<init>(EntityKey.java:54) 
    at org.hibernate.internal.AbstractSharedSessionContract.generateEntityKey(AbstractSharedSessionContract.java:459) 
    at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:162) 
    at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125) 
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener.saveWithGeneratedId(JpaPersistEventListener.java:67) 
    at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:189) 
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:132) 
    at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:788) 
    at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:753) 
    at org.hibernate.jpa.event.internal.core.JpaPersistEventListener$1.cascade(JpaPersistEventListener.java:80) 
    at org.hibernate.engine.internal.Cascade.cascadeToOne(Cascade.java:391) 
    at org.hibernate.engine.internal.Cascade.cascadeAssociation(Cascade.java:316) 

我跟踪的执行和它似乎异常是由variant类引起的具有空的hashCode这不应该是因为我居住的变体具有不同的情况下名称为休眠区分（尽管Id尚不知道）每个子产品（我试图保存2个子产品在一个产品下）。每个subProduct将有两个productVariantMap。

我期望剩下1个产品行，2个子产品，4个产品变体映射行和2个变体行。 是否有可能在JPA中一直坚持整个关系？ 非常感谢

Answer 1

在JPA哈希和等于方法必须基于主键。而不是使用框架来生成hash（）equals（）并实现它。

public boolean equals(Object o) { 
if (this == o) return true; 
if (o == null || !(o instanceof Person)) 
    return false; 

Person other = (Person)o; 

if (id == other.getId()) return true; 
if (id == null) return false; 

// equivalence by id 
return id.equals(other.getId()); 
} 

public int hashCode() { 
    if (id != null) { 
     return id.hashCode(); 
    } else { 
     return super.hashCode(); 
    } 
} 

其他备注： @Embedable类是实体在同一个数据库表中的一部分。嵌入式和其父母之间不需要关联。删除@ManyToOne