hibernate 翻译
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An instance of?Configuration?allows(允许) the application to specify properties and mapping documents to be used when creating a?SessionFactory. Usually(通常) an application will create a single?Configuration, build a single instance of?SessionFactoryand then instantiate?Sessions in threads servicing client requests. The?Configuration?is meant(意味) only as an initialization(初始化)-time object.?SessionFactorys are immutable(不可变) and do not retain(保留) any association(协会)?back to the?Configuration.
A new?Configuration?will use the properties specified in?hibernate.properties?by default.
NOTE : This will be replaced(取代) by use of?ServiceRegistryBuilder?and?MetadataSources?instead(替换) after the 4.0 release(发布) at which point this class will become deprecated and scheduled(预期) for removal in 5.0. See?HHH-6183,?HHH-2578?and?HHH-6586?for details
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Create a?SessionFactory?using the properties and mappings in this configuration. The?SessionFactory?will be immutable(不可变), so changes made to?thisConfiguration?after building the?SessionFactory?will not affect(影响) it.
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The main contract here is the creation of?Session?instances. Usually an application has a single?SessionFactory?instance and threads servicing(为...服务) client requests obtain(获得)?Session?instances from this factory.
The internal state of a?SessionFactory?is immutable. Once it is created this internal state is set. This internal state includes all of the metadata(元数据) about Object/Relational(相关的) Mapping.
Implementors(实施者)?must?be threadsafe.
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The main runtime interface between a Java application and Hibernate. This is the central API class abstracting the notion(概念) of a persistence(持续)?service.
The lifecycle(生命周期) of a?Session?is bounded(有界限的) by the beginning and end of a logical transaction. (Long transactions might(可能) span(跨越) several(几个) database transactions.)
The main function of the?Session?is to offer(提供) create, read and delete operations for instances of mapped entity classes. Instances may exist in one of three states:
transient(瞬时):?never persistent(持久的), not associated(相关) with any?Session
persistent(持久):?associated(关联) with a unique?Session
detached(托管):?previously(预先) persistent, not associated with any?Session
Transient(瞬时) instances may be made persistent(持久) by calling?save(),?persist()?or?saveOrUpdate(). Persistent(持久) instances may be made transient by calling?delete(). Any instance returned by a?get()?or?load()?method is persistent. Detached(托管) instances may be made persistent by calling?update(),?saveOrUpdate(),?lock()?orreplicate(). The state of a transient(瞬时) or detached(瞬时) instance may also be made persistent(持久) as a new persistent(持久) instance by calling?merge().
save()?and?persist()?result in an SQL?INSERT,?delete()?in an SQL?DELETE?and?update()?or?merge()?in an SQL?UPDATE. Changes to?persistent?instances are detected at flush time and also result in an SQL?UPDATE.?saveOrUpdate()?and?replicate()?result in either an?INSERT?or an?UPDATE.
It is not intended that implementors be threadsafe. Instead each thread/transaction should obtain its own instance from a?SessionFactory.
A?Session?instance is serializable if its persistent classes are serializable.
A typical transaction should use the following idiom:
Session sess = factory.openSession(); Transaction tx; try { tx = sess.beginTransaction(); //do some work ... tx.commit(); } catch (Exception e) { if (tx!=null) tx.rollback(); throw e; } finally { sess.close(); }
If the?Session?throws an exception, the transaction must be rolled back and the session discarded. The internal state of the?Session?might not be consistent with the database after the exception occurs.