休眠中雙向關係的問題

Question

我有兩個實體：Sale和SaleProduct。

我試圖堅持銷售實體，但我不知道如何向它提供服務，因爲我總是嘗試保存Sale ir需要SaleProduct。

這是銷售實體：

@Entity 
@Data 
@NoArgsConstructor 
@AllArgsConstructor 
public class Sale { 

    @Id 
    @GeneratedValue(strategy = GenerationType.SEQUENCE) 
    private long id; 

    @NotNull(message = "Sale product!") 
    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY) 
    @JoinColumn(name = "SALE_ID") 
    private List<SaleProduct> products; 

    @NotNull(message = "Sale needs some value!") 
    private int saleValue; 

    private Date creationDate = new Date(); 

} 

這裏是SaleProduct實體：

@Entity 
@AllArgsConstructor 
@NoArgsConstructor 
@Data 
@Builder 
public class SaleProduct { 

    @Id 
    @GeneratedValue(strategy = GenerationType.SEQUENCE) 
    private long id; 

    private int quantity; 

    @NotNull(message = "Insert the product, please") 
    @ManyToOne(fetch = FetchType.EAGER) 
    private Product product; 

    @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY) 
    private Sale sale; 

} 

我試圖堅持出售用這種方法：

public void insertSale(Sale sale) throws Exception { 
     Product product = manager.find(Product.class, 2L); 
     SaleProduct saleProduct = new SaleProduct(); 
     saleProduct.setProduct(product); 
     sale.setProducts(Arrays.asList(saleProduct)); 
     saleProduct.setSale(sale); 
     manager.persist(sale); 
    } 

我我正在發送這個JSON：

{ 
    "saleValue" : "200" 
} 

當我嘗試選擇我創建的銷售我得到這些錯誤：

Caused by: com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: com.tax.entity.Sale.products, could not initialize proxy - no Session (through reference chain: java.util.ArrayList[0]->com.tax.entity.Sale["products"]) 
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:210) 
at com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:177) 
at com.fasterxml.jackson.databind.ser.std.StdSerializer.wrapAndThrow(StdSerializer.java:190) 
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:674) 
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:156) 
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serializeContentsUsing(CollectionSerializer.java:160) 
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serializeContents(CollectionSerializer.java:102) 
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:94) 
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:24) 
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:251) 
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:846) 
at org.jboss.resteasy.plugins.providers.jackson.ResteasyJackson2Provider.writeTo(ResteasyJackson2Provider.java:207) 
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.writeTo(AbstractWriterInterceptorContext.java:131) 
at org.jboss.resteasy.core.interception.ServerWriterInterceptorContext.writeTo(ServerWriterInterceptorContext.java:60) 
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:120) 
at org.jboss.resteasy.security.doseta.DigitalSigningInterceptor.aroundWriteTo(DigitalSigningInterceptor.java:145) 
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:124) 
at org.jboss.resteasy.plugins.interceptors.encoding.GZIPEncodingInterceptor.aroundWriteTo(GZIPEncodingInterceptor.java:100) 
at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:124) 
at org.jboss.resteasy.core.ServerResponseWriter.writeNomapResponse(ServerResponseWriter.java:98) 
at org.jboss.resteasy.core.SynchronousDispatcher.writeResponse(SynchronousDispatcher.java:466) 
... 33 more 

Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.tax.entity.Sale.products, could not initialize proxy - no Session 
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:567) 
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:205) 
at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:146) 
at org.hibernate.collection.internal.PersistentBag.size(PersistentBag.java:261) 
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:88) 
at com.fasterxml.jackson.databind.ser.std.CollectionSerializer.serialize(CollectionSerializer.java:24) 
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:575) 
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:666) 
... 50 more 

還有一個問題：當我saleProduct.setSale(sale);我得到這個異常：發生com.sun.jdi.InvocationException調用方法

Answer 1

爲了實現雙向映射，你得有在實體銷售使用

在OneToMany註釋

「的mappedBy」屬性

Answer 2

1. 的@JoinColumn註釋必須在onwing側的關係，也就是說，它應該是對@ManyToOne註釋：

   @ManyToOne(cascade = CascadeType.ALL, fetch = FetchType.LAZY) 
   @JoinColumn(name = "SALE_ID") 
   private Sale sale; 
   

2. 的mappedBy屬性必須被放置在逆側，即是其中@OneToMany註解用於：

   @OneToMany(mappedBy="sale" cascade = CascadeType.ALL, fetch = FetchType.EAGER) 
   private List<SaleProduct> products; 
   

3. 創建的Sale一個實例，比如sale。

4. 創建一個SaleProduct的實例，比如saleProduct。

5. 將saleProduct加入列表products。 （我不知道你爲什麼給列表products命名，即使它包含SaleProduct s）。

6. 指定sale至saleProduct：saleProduct.setSale(sale)。現在兩個實體實例都連接在一起。

7. ，最後堅持：entityManager.persist(sale);

Answer 3

由於異常說

No validator could be found for constraint 'javax.validation.constraints.Size' validating type 'com.tax.entity.Product'. Check configuration for 'product' 

所以從外地 「產品」 刪除@Size，因爲它不是一個集合場。你可以把它放在關係的另一邊"Sale.products"