休眠：如何获取会话中当前所有对象的列表

Question

我变得好，老又怕TransientObjectException，而且在这种情况下经常发生，我在查找导致问题的代码中存在哪些细微的错误时遇到了问题。

我的问题是：有没有办法获取当前Hibernate会话中每个对象的列表？

当我得到这个问题的答案时，我可能会解决当前的问题，但是无论如何，能够列出会话中的所有内容将在下次发生时大有帮助。

Answer 1

Hibernate不会向公众公开其内部信息，因此您不会在公共API中找到要搜索的内容。但是，您可以在Hibernate接口的实现类中找到答案：此方法（摘自http://code.google.com/p/bo2/source/browse/trunk/Bo2ImplHibernate/main/gr/interamerican/bo2/
impl / open / hibernate /
HibernateBo2Utils.java

）将告知会话中是否存在对象：

public static Object getFromSession
        (Serializable identifier, Class<?> clazz, Session s) {              
    String entityName = clazz.getName();
    if(identifier == null) {
       return null;
    }      
    SessionImplementor sessionImpl = (SessionImplementor) s;
    EntityPersister entityPersister = sessionImpl.getFactory().getEntityPersister(entityName);
    PersistenceContext persistenceContext = sessionImpl.getPersistenceContext();
    EntityKey entityKey = new EntityKey(identifier, entityPersister, EntityMode.POJO);
    Object entity = persistenceContext.getEntity(entityKey);
    return entity;
    }

如果进一步深入研究，您将看到PersistenceContext的唯一实现是org.hibernate.engine.StatefulPersistenceContext。此类具有以下集合：

// Loaded entity instances, by EntityKey
private Map entitiesByKey;

// Loaded entity instances, by EntityUniqueKey
private Map entitiesByUniqueKey;

// Identity map of EntityEntry instances, by the entity instance
private Map entityEntries;

// Entity proxies, by EntityKey
private Map proxiesByKey;

// Snapshots of current database state for entities
// that have *not* been loaded
private Map entitySnapshotsByKey;

// Identity map of array holder ArrayHolder instances, by the array instance
private Map arrayHolders;

// Identity map of CollectionEntry instances, by the collection wrapper
private Map collectionEntries;

// Collection wrappers, by the CollectionKey
private Map collectionsByKey; //key=CollectionKey, value=PersistentCollection

// Set of EntityKeys of deleted objects
private HashSet nullifiableEntityKeys;

// properties that we have tried to load, and not found in the database
private HashSet nullAssociations;

// A list of collection wrappers that were instantiating during result set
// processing, that we will need to initialize at the end of the query
private List nonlazyCollections;

// A container for collections we load up when the owning entity is not
// yet loaded ... for now, this is purely transient!
private Map unownedCollections;

// Parent entities cache by their child for cascading
// May be empty or not contains all relation 
private Map parentsByChild;

因此，您需要做的是将PersistenceContext强制转换为StatefulPersistenceContext，然后使用反射来获取所需的私有集合，然后对其进行迭代。

我强烈建议您仅在调试代码上执行此操作。这不是公共API，它可能会因较新的Hibernate版本而制止。