Fehler verzögertes Laden: com.fasterxml.jackson.databind.JsonMappingException: failed träge, um eine Sammlung von Rolle zu initialisieren

Question

ich mit Sammlungen ein Entity, und ich würde Last Entity in faul mag, aber ich habe Fehler:

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 

Und meine Entitäten wie:

@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>(); 

} 

In meinem DAO:

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

    return folders; 
} 

So, wie ich es beheben kann in JPA? Was ist falsch, wenn ich meine Methode anrufen retrieveFolder?

Vielen Dank

Answer 1

Sie müssen die Sammelanforderungen initialisieren.

Sie könnten folders.getRequests(). Iterator() aufrufen, die das Laden der Anfragen auslösen würde.

Aber der beste Weg ist eiter eine JPQL Abfrage mit einem JOIN FETCH auf Anfragen zu schreiben, dass die Sammlung mit Spannung geladen wird:

SELECT f FROM Folder f JOIN FETCH f.requests r 

oder ein EntityGraph verwenden, die das gleiche tun.

Schauen Sie sich die Hibernate-Dokumentation an und suchen Sie nach JOIN FETCH und EntityGraph.

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