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EntityManager鐨勫畾涔?br>The EntityManager manages the O/R mapping between a fixed set of entity classes and an underlying data source.
It provides APIs for creating queries, finding objects, synchronizing objects, and inserting objects into the database.
It also can provide caching and manage the interaction between an entity and transactional services in a Java EE environment such as JTA.
The EntityManager is tightly integrated with Java EE and EJB but is not limited to this environment; it can be used in plain Java programs.
An EntityManager maps a fixed set of classes to a particular database. This set of classes is called a persistence unit .
In Java SE, entity managers are created using a javax.persistence.EntityManagerFactory
Example錛?br> EntityManagerFactory factory = Persistence.createEntityManagerFactory("titan", map);
EntityManager manager = factory.createEntityManager();
鍦↗ava SE鐜涓紝浣跨敤瀹孍ntityManagerFactory鍚庯紝鏈濂藉皢鍏跺叧闂紝浠ラ噴鏀懼叾鍗犳湁鐨勮祫婧愩?br>
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public interface EntityManager {
public void persist(Object entity);
public <T> T find(Class <T> entityClass, Object primaryKey);
public <T> T getReference(Class <T> entityClass, Object primaryKey);
public <T> T merge(T entity);
public void remove(Object entity);
public void lock(Object entity, LockModeType lockMode);
public void refresh(Object entity);
public boolean contains(Object entity);
public void clear( );
public void joinTransaction( );
public void flush( );
public FlushModeType getFlushMode( );
public void setFlushMode(FlushModeType type);
public Query createQuery(String queryString);
public Query createNamedQuery(String name);
public Query createNativeQuery(String sqlString);
public Query createNativeQuery(String sqlString, String resultSetMapping);
public Query createNativeQuery(String sqlString, Class resultClass);
public Object getDelegate( );
public void close( );
public boolean isOpen( );
}
Persistence context鐨勫畾涔?br>A persistence context is a set of managed entity object instances.
Persistence contexts are managed by an entity manager.
There are two types of persistence contexts: transaction-scoped and extended persistence contexts.
A persistence context can be created by calling the EntityManagerFactory.createEntityManager( ) method. The returned EntityManager instance represents an extended persistence context. If the EntityManagerFactory is JTA-enabled, then you have to explicitly enlist the EntityManager instance within a transaction by calling the EntityManager.joinTransaction( ) method. If you do not enlist the EntityManager within the JTA transaction, then changes you make to your entities are not synchronized with the database.FlushModeType鐨勫惈涔?br>
FlushModeType榛樿涓篈UTO妯″紡錛屽綋涓篈UTO鏃訛紝鍦ㄤ竴涓煡璇㈣鎵ц鍓嶏紝浼氳嚜鍔ㄥ皢鍙樺寲鎻愪氦鍒版暟鎹簱涓紝鍗寵皟鐢╢lush()鏂規硶銆備絾鏄皟鐢╢ind()鎴杇etreference()鏂規硶鏃訛紝騫朵笉浼氭墽琛岃嚜鍔ㄦ彁浜ゃ傚綋涓篊OMMIT妯″紡鏃訛紝浠呬粎鍦ㄤ簨鍔℃彁浜ゆ椂錛屼細灝嗗彉鍖栨彁浜ゅ埌鏁版嵁搴撲腑銆?br>EJB3涓殑瀹炰綋娉ㄨВ瑙勮寖鍙傝濡備笅閾炬帴
http://wiki.redsaga.com/confluence/display/HART/Home
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