javax.persistence

Interface EntityManager

public interface EntityManager

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.

Author:

Emmanuel Bernard

Method Summary

Methods

Modifier and Type	Method and Description
void	clear() Clear the persistence context, causing all managed entities to become detached.
void	close() Close an application-managed EntityManager.
boolean	contains(Object entity) Check if the instance belongs to the current persistence context.
Query	createNamedQuery(String name) Create an instance of Query for executing a named query (in EJB QL or native SQL).
Query	createNativeQuery(String sqlString) Create an instance of Query for executing a native SQL statement, e.g., for update or delete.
Query	createNativeQuery(String sqlString, Class resultClass) Create an instance of Query for executing a native SQL query.
Query	createNativeQuery(String sqlString, String resultSetMapping) Create an instance of Query for executing a native SQL query.
Query	createQuery(String ejbqlString) Create an instance of Query for executing an EJB QL statement.
<T> T	find(Class<T> entityClass, Object primaryKey) Find by primary key.
void	flush() Synchronize the persistence context to the underlying database.
Object	getDelegate() Return the underlying provider object for the EntityManager, if available.
FlushModeType	getFlushMode() Get the flush mode that applies to all objects contained in the persistence context.
<T> T	getReference(Class<T> entityClass, Object primaryKey) Get an instance, whose state may be lazily fetched.
EntityTransaction	getTransaction() Return the resource-level transaction object.
boolean	isOpen() Determine whether the EntityManager is open.
void	joinTransaction() Indicate to the EntityManager that a JTA transaction is active.
void	lock(Object entity, LockModeType lockMode) Set the lock mode for an entity object contained in the persistence context.
<T> T	merge(T entity) Merge the state of the given entity into the current persistence context.
void	persist(Object entity) Make an entity instance managed and persistent.
void	refresh(Object entity) Refresh the state of the instance from the database, overwriting changes made to the entity, if any.
void	remove(Object entity) Remove the entity instance.
void	setFlushMode(FlushModeType flushMode) Set the flush mode that applies to all objects contained in the persistence context.

Method Detail

persist

void persist(Object entity)

Make an entity instance managed and persistent.

Parameters:

entity -

Throws:

EntityExistsException - if the entity already exists. (The EntityExistsException may be thrown when the persist operation is invoked, or the EntityExistsException or another PersistenceException may be thrown at commit time.)

IllegalStateException - if this EntityManager has been closed.

IllegalArgumentException - if not an entity

TransactionRequiredException - if invoked on a container-managed entity manager of type PersistenceContextType.TRANSACTION and there is no transaction.

merge

<T> T merge(T entity)

Merge the state of the given entity into the current persistence context.

Parameters:

entity -

Returns:

the instance that the state was merged to

Throws:

IllegalStateException - if this EntityManager has been closed

IllegalArgumentException - if instance is not an entity or is a removed entity

TransactionRequiredException - if invoked on a container-managed entity manager of type PersistenceContextType.TRANSACTION and there is no transaction.

remove

void remove(Object entity)

Remove the entity instance.

Parameters:

entity -

Throws:

IllegalStateException - if this EntityManager has been closed

IllegalArgumentException - if not an entity or if a detached entity

TransactionRequiredException - if invoked on a container-managed entity manager of type PersistenceContextType.TRANSACTION and there is no transaction.

find

<T> T find(Class<T> entityClass,
         Object primaryKey)

Find by primary key.

Parameters:

entityClass -

primaryKey -

Returns:

the found entity instance or null if the entity does not exist

Throws:

IllegalStateException - if this EntityManager has been closed

IllegalArgumentException - if the first argument does not denote an entity type or the second argument is not a valid type for that entity?s primary key

getReference

<T> 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.

Parameters:

entityClass -

primaryKey -

Returns:

the found entity instance

Throws:

IllegalStateException - if this EntityManager has been closed

IllegalArgumentException - if the first argument does not denote an entity type or the second argument is not a valid type for that entity?s primary key

EntityNotFoundException - if the entity state cannot be accessed

flush

void flush()

Synchronize the persistence context to the underlying database.

Throws:

IllegalStateException - if this EntityManager has been closed

TransactionRequiredException - if there is no transaction

PersistenceException - if the flush fails

setFlushMode

void setFlushMode(FlushModeType flushMode)

Set the flush mode that applies to all objects contained in the persistence context.

Parameters:

flushMode -

Throws:

IllegalStateException - if this EntityManager has been closed

getFlushMode

FlushModeType getFlushMode()

Get the flush mode that applies to all objects contained in the persistence context.

Returns:

flushMode

Throws:

IllegalStateException - if this EntityManager has been closed

lock

void lock(Object entity,
        LockModeType lockMode)

Set the lock mode for an entity object contained in the persistence context.

Parameters:

entity -

lockMode -

Throws:

IllegalStateException - if this EntityManager has been closed

PersistenceException - if an unsupported lock call is made

IllegalArgumentException - if the instance is not an entity or is a detached entity

TransactionRequiredException - if there is no transaction

refresh

void refresh(Object entity)

Refresh the state of the instance from the database, overwriting changes made to the entity, if any.

Parameters:

entity -

Throws:

IllegalStateException - if this EntityManager has been closed

IllegalArgumentException - if not an entity or entity is not managed

TransactionRequiredException - if invoked on a container-managed entity manager of type PersistenceContextType.TRANSACTION and there is no transaction.

EntityNotFoundException - if the entity no longer exists in the database

clear

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.

Throws:

IllegalStateException - if this EntityManager has been closed

contains

boolean contains(Object entity)

Check if the instance belongs to the current persistence context.

Parameters:

entity -

Returns:

true if the instance belongs to the current persistence context.

Throws:

IllegalStateException - if this EntityManager has been closed

IllegalArgumentException - if not an entity

createQuery

Query createQuery(String ejbqlString)

Create an instance of Query for executing an EJB QL statement.

Parameters:

ejbqlString - an EJB QL query string

Returns:

the new query instance

Throws:

IllegalStateException - if this EntityManager has been closed

IllegalArgumentException - if query string is not valid

createNamedQuery

Query createNamedQuery(String name)

Create an instance of Query for executing a named query (in EJB QL or native SQL).

Parameters:

name - the name of a query defined in metadata

Returns:

the new query instance

Throws:

IllegalStateException - if this EntityManager has been closed

IllegalArgumentException - if a query has not been defined with the given name

createNativeQuery

Query createNativeQuery(String sqlString)

Create an instance of Query for executing a native SQL statement, e.g., for update or delete.

Parameters:

sqlString - a native SQL query string

Returns:

the new query instance

Throws:

IllegalStateException - if this EntityManager has been closed

createNativeQuery

Query createNativeQuery(String sqlString,
                      Class resultClass)

Create an instance of Query for executing a native SQL query.

Parameters:

sqlString - a native SQL query string

resultClass - the class of the resulting instance(s)

Returns:

the new query instance

Throws:

IllegalStateException - if this EntityManager has been closed

createNativeQuery

Query createNativeQuery(String sqlString,
                      String resultSetMapping)

Create an instance of Query for executing a native SQL query.

Parameters:

sqlString - a native SQL query string

resultSetMapping - the name of the result set mapping

Returns:

the new query instance

Throws:

IllegalStateException - if this EntityManager has been closed

joinTransaction

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.

Throws:

IllegalStateException - if this EntityManager has been closed

TransactionRequiredException - if there is no transaction.

getDelegate

Object getDelegate()

Return the underlying provider object for the EntityManager, if available. The result of this method is implementation specific

Throws:

IllegalStateException - if this EntityManager has been closed

close

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.

Throws:

IllegalStateException - if the EntityManager is container-managed or has been already closed

isOpen

boolean isOpen()

Determine whether the EntityManager is open.

Returns:

true until the EntityManager has been closed.

getTransaction

EntityTransaction getTransaction()

Return the resource-level transaction object. The EntityTransaction instance may be used serially to begin and commit multiple transactions.

Returns:

EntityTransaction instance

Throws:

IllegalStateException - if invoked on a JTA EntityManager.