Neil的备忘录

Transactional persistent instances (ie. objects loaded, saved, created or queried by the Session) may be manipulated by the application and any changes to persistent state will be persisted when the Session is flushed (discussed later in this chapter). There is no need to call a particular method (like update(), which has a different purpose) to make your modifications persistent. So the most straightforward way to update the state of an object is to load() it, and then manipulate it directly, while the Session is open:

DomesticCat cat = (DomesticCat) sess.load( Cat.class, new Long(69) );
cat.setName("PK");
sess.flush();  // changes to cat are automatically detected and persisted

Sometimes this programming model is inefficient since it would require both an SQL SELECT (to load an object) and an SQL UPDATE (to persist its updated state) in the same session. Therefore Hibernate offers an alternate approach, using detached instances.

Note that Hibernate does not offer its own API for direct execution of UPDATE or DELETE statements. Hibernate is a state management service, you don't have to think in statements to use it. JDBC is a perfect API for executing SQL statements, you can get a JDBC Connection at any time by calling session.connection(). Furthermore, the notion of mass operations conflicts with object/relational mapping for online transaction processing-oriented applications. Future versions of Hibernate may however provide special mass operation functions. See Chapter 13, Batch processing for some possible batch operation tricks.