java - 带有 Map 的 JPA NullPointerException

Question

我有以下使用 EclipseLink 2.5.1 的 JPA 映射设置

@Entity
@Table(name = "ACCOUNTS")
public class Account extends AbstractAggregateRoot<Long> {
...
    private AccountMetadata metadata = new AccountMetadata();
}

@Embeddable
@Access(AccessType.PROPERTY)
public class AccountMetadata extends Metadata {

    @ElementCollection(fetch=FetchType.EAGER)
    @CollectionTable(name="ACCOUNT_METADATA",
            joinColumns=@JoinColumn(table="ACCOUNTS", referencedColumnName="ID", name="ACCOUNT_ID"))
    @Column(name= "MD_VALUE")
    public Map<Key,String> getMetadata() {
        return this.metadata;
    }

    public void setMetadata(Map<Key,String> md) {
        this.metadata = md;
    }
}

@Embeddable
public class Metadata implements Serializable {

....

    protected Map<Key,String> metadata = new HashMap<>();

    @Embeddable
    @Access(AccessType.FIELD)
    public static class Key {
        @Enumerated(EnumType.STRING)
        @Column(name = "KEY_NS")
        private Namespace ns;
        @Column(name = "KEY_NAME")
        private String name;

    ...

    }    
}

启用缓存后，一切都很好。当我通过将以下内容添加到持久性 XML 来禁用缓存时

<shared-cache-mode>NONE</shared-cache-mode>

我在尝试提交时收到以下错误。

Caused by: Exception [EclipseLink-69] (Eclipse Persistence Services - 2.5.1.v20130918-f2b9fc5): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: A NullPointerException was thrown while extracting a value from the instance variable [ns] in the object [oracle.cloudstorage.common.domain.Metadata$Key].
Internal Exception: java.lang.NullPointerException
Mapping: org.eclipse.persistence.mappings.DirectToFieldMapping[ns-->KEY_NS]
Descriptor: RelationalDescriptor(oracle.cloudstorage.common.domain.Metadata$Key --> [])
    at org.eclipse.persistence.exceptions.DescriptorException.nullPointerWhileGettingValueThruInstanceVariableAccessor(DescriptorException.java:1277)
    at org.eclipse.persistence.internal.descriptors.InstanceVariableAttributeAccessor.getAttributeValueFromObject(InstanceVariableAttributeAccessor.java:88)
    at org.eclipse.persistence.mappings.DatabaseMapping.getAttributeValueFromObject(DatabaseMapping.java:615)
    at org.eclipse.persistence.mappings.foundation.AbstractDirectMapping.compareObjects(AbstractDirectMapping.java:407)
    at org.eclipse.persistence.mappings.foundation.AbstractDirectMapping.compareForChange(AbstractDirectMapping.java:381)
    at org.eclipse.persistence.descriptors.changetracking.DeferredChangeDetectionPolicy.createObjectChangeSetThroughComparison(DeferredChangeDetectionPolicy.java:186)
    at org.eclipse.persistence.descriptors.changetracking.DeferredChangeDetectionPolicy.createObjectChangeSet(DeferredChangeDetectionPolicy.java:146)
    at org.eclipse.persistence.descriptors.changetracking.DeferredChangeDetectionPolicy.calculateChanges(DeferredChangeDetectionPolicy.java:91)
    at org.eclipse.persistence.descriptors.changetracking.DeferredChangeDetectionPolicy.calculateChangesForExistingObject(DeferredChangeDetectionPolicy.java:56)
    at org.eclipse.persistence.internal.sessions.UnitOfWorkImpl.calculateChanges(UnitOfWorkImpl.java:664)
    at org.eclipse.persistence.internal.sessions.RepeatableWriteUnitOfWork.writeChanges(RepeatableWriteUnitOfWork.java:438)
    at org.eclipse.persistence.internal.jpa.EntityManagerImpl.flush(EntityManagerImpl.java:863)

有没有人遇到过这个问题？我尝试了不同的缓存参数，唯一似乎有效的参数是启用缓存

<shared-cache-mode>DISABLE_SELECTIVE</shared-cache-mode>

并将其添加到实体的顶部

@Cache(refreshAlways=true)

Answer 1

我遇到了同样的问题。在使用 @Embedded 的 @ElementCollection 时，Eclipselink 似乎有很多问题。

可能实现依赖于内部缓存来访问该对象而不是将它们保存在 UnitOfWork 中，因此如果禁用缓存，您将获得 NPE。启用缓存并不能保证您不会获得 NPE:它也会在处理大型数据集时抛出。

我已经提交了2个与此问题相关的BUG: https://bugs.eclipse.org/bugs/show_bug.cgi?id=441498 https://bugs.eclipse.org/bugs/show_bug.cgi?id=442228

目前的变通方法是仅将 @ElementCollections 用于原始成员类型，并使用 @OneToMany 映射对象。