エラー遅延ロード：com.fasterxml.jackson.databind.JsonMappingExceptionは：怠惰な役割

Question

のコレクションを初期化できませんでした私はコレクションを持つエンティティを持っている、と私は怠け者で、負荷のエンティティをしたいと思いますが、私はエラーを得た：

Caused by: com.fasterxml.jackson.databind.JsonMappingException: failed to lazily initialize a collection of role: lu.entities.folders.Folders.requests, could not initialize proxy - no Session (through reference chain: lu.entities.folders.Folders.requests) 
    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.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:129) 
    at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:851) 
    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) 
    ... 38 more 
Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: lu.pgd.ccpd.entities.folders.Folders.requests, could not initialize proxy - no Session 
    at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:587) 
    at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:204) 
    at org.hibernate.collection.internal.AbstractPersistentCollection.readSize(AbstractPersistentCollection.java:148) 
    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) 
    ... 51 more 

そして、私のエンティティのように：私のDAOで

@Entity 
@Table(name = "FOLDER_FR") 
@JsonIdentityInfo(scope=Folders.class, generator = ObjectIdGenerators.PropertyGenerator.class, property="id") 
public class Folders implements Serializable { 
    private static final long serialVersionUID = 1L; 
    @Id 
    @GeneratedValue(strategy = GenerationType.SEQUENCE) 
    @Column(name = "FR_ID") 
    private Long id; 

    @LazyCollection(LazyCollectionOption.TRUE) 
    @JsonIgnore 
    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true) 
    @JoinTable(name = "M_REQUESTFOLDER_RR", joinColumns = { 
      @JoinColumn(name = "RR_FOLDER", referencedColumnName = "FR_ID") }, inverseJoinColumns = { 
        @JoinColumn(name = "RR_REQUEST", referencedColumnName = "RS_ID") }) 
    private List<Requests> requests = new ArrayList<Requests>(); 

} 

：だから

@Override 
public Folders retrieveFolder(Long id) throws PersistenceException { 
    Folders folders = entityManager.find(Folders.class, id); 

    return folders; 
} 

私はそれを解決する方法JPAで？ 私のメソッドを呼び出すと何が問題になりますretrieveFolder？

ありがとうございました

Answer 1

収集要求を初期化する必要があります。

要求のロードをトリガーするfolders.getRequests（）。iterator（）を呼び出すことができます。

しかし、最善の方法は、熱心にそのコレクションをロードする要求にFETCH JOINをしてJPQLクエリを記述するeiterです：

SELECT f FROM Folder f JOIN FETCH f.requests r 

それとも同じことをするでしょうEntityGraphを使用。

Hibernateのドキュメントを見て、JOIN FETCHとEntityGraphを検索してください。

http://docs.jboss.org/hibernate/orm/5.2/userguide/html_single/Hibernate_User_Guide.html