在Hibernate中query.uniqueResult（）和session.load（）之间有什么区别？

Question

Can anyone tell me what's the difference between this code:

// This following method checks if there is an open session
// and if yes - returns it,  if not - opens a new session. 
Session session = getSession();
Query query = session.createQuery("from Entity e where e.id = 1");
Entity object = (Entity)query.uniqueResult(); 

and this:

 Session session = getSession();
 Entity object = (Entity)session.load(Entity.class, new Integer(1));

Does the first method return a proxy object? And if I call it again does it hit the database?

Answer 1

There are some differences (as of Hibernate 5.2.6).

session.load()

• It only searchs by id assuming that the Entity exists
• It will ALWAYS return a “ proxy ” (Hibernate term) without hitting the database. In Hibernate, proxy is an object with the given identifier value, its properties are not initialized yet, it just looks like a temporary fake object.
• Use this only to retrieve an instance that you assume exists, where non-existence would be an ObjectNotFoundException .

query.uniqueResult()

• You can query with complex conditions, not only by the id
• Convenience method to return a single instance that matches the query, or null if the query returns no results.
• It will return an entity with its collection initialized or not depending on the FetchType .