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public interface: EntityManager [javadoc | source] Interface used to interact with the persistence context. An EntityManager instance is associated with a persistence context. A persistence context is a set of entity instances in which for any persistent entity identity there is a unique entity instance. Within the persistence context, the entity instances and their lifecycle are managed. This interface defines the methods that are used to interact with the persistence context. The EntityManager API is used to create and remove persistent entity instances, to find entities by their primary key, and to query over entities. The set of entities that can be managed by a given EntityManager instance is defined by a persistence unit. A persistence unit defines the set of all classes that are related or grouped by the application, and which must be colocated in their mapping to a single database.
Method from javax.persistence.EntityManager Summary:
clear,   close,   contains,   createNamedQuery,   createNativeQuery,   createNativeQuery,   createNativeQuery,   createQuery,   find,   flush,   getDelegate,   getFlushMode,   getReference,   getTransaction,   isOpen,   joinTransaction,   lock,   merge,   persist,   refresh,   remove,   setFlushMode
Method from javax.persistence.EntityManager Detail:
 public  void clear()
    Clear the persistence context, causing all managed entities to become detached. Changes made to entities that have not been flushed to the database will not be persisted.
 public  void close()
    Close an application-managed EntityManager. After the close method has been invoked, all methods on the EntityManager instance and any Query objects obtained from it will throw the IllegalStateException except for getTransaction and isOpen (which will return false). If this method is called when the EntityManager is associated with an active transaction, the persistence context remains managed until the transaction completes.
 public boolean contains(Object entity)
    Check if the instance belongs to the current persistence context.
 public Query createNamedQuery(String name)
    Create an instance of Query for executing a named query (in EJB QL or native SQL).
 public Query createNativeQuery(String sqlString)
    Create an instance of Query for executing a native SQL statement, e.g., for update or delete.
 public Query createNativeQuery(String sqlString,
    Class resultClass)
    Create an instance of Query for executing a native SQL query.
 public Query createNativeQuery(String sqlString,
    String resultSetMapping)
    Create an instance of Query for executing a native SQL query.
 public Query createQuery(String ejbqlString)
    Create an instance of Query for executing an EJB QL statement.
 public T find(Class<T> entityClass,
    Object primaryKey)
    Find by primary key.
 public  void flush()
    Synchronize the persistence context to the underlying database.
 public Object getDelegate()
    Return the underlying provider object for the EntityManager, if available. The result of this method is implementation specific
 public FlushModeType getFlushMode()
    Get the flush mode that applies to all objects contained in the persistence context.
 public T getReference(Class<T> entityClass,
    Object primaryKey)
    Get an instance, whose state may be lazily fetched. If the requested instance does not exist in the database, the EntityNotFoundException is thrown when the instance state is first accessed. (The persistence provider runtime is permitted to throw the EntityNotFoundException when getReference is called.) The application should not expect that the instance state will be available upon detachment, unless it was accessed by the application while the entity manager was open.
 public EntityTransaction getTransaction()
    Return the resource-level transaction object. The EntityTransaction instance may be used serially to begin and commit multiple transactions.
 public boolean isOpen()
    Determine whether the EntityManager is open.
 public  void joinTransaction()
    Indicate to the EntityManager that a JTA transaction is active. This method should be called on a JTA application managed EntityManager that was created outside the scope of the active transaction to associate it with the current JTA transaction.
 public  void lock(Object entity,
    LockModeType lockMode)
    Set the lock mode for an entity object contained in the persistence context.
 public T merge(T entity)
    Merge the state of the given entity into the current persistence context.
 public  void persist(Object entity)
    Make an entity instance managed and persistent.
 public  void refresh(Object entity)
    Refresh the state of the instance from the database, overwriting changes made to the entity, if any.
 public  void remove(Object entity)
    Remove the entity instance.
 public  void setFlushMode(FlushModeType flushMode)
    Set the flush mode that applies to all objects contained in the persistence context.