4640 words

javax.persistence.EntityManager - JPA interface

javax.persistence
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. 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.

Since:
JPA 1.0
See Also:
Query
TypedQuery
CriteriaQuery
PersistenceContext
Learn how to use EntityManager in Chapter 3 of the ObjectDB/JPA manual.
void clear()
Clear the persistence context, causing all managed entities to become detached.
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.
Since:
JPA 1.0
void close()
Close an application-managed entity manager.
Close an application-managed entity manager. After the close method has been invoked, all methods on the EntityManager instance and any Query and TypedQuery objects obtained from it will throw the IllegalStateException except for getProperties, getTransaction, and isOpen (which will return false). If this method is called when the entity manager is associated with an active transaction, the persistence context remains managed until the transaction completes.
Throws:
IllegalStateException - if the entity manager is container-managed
Since:
JPA 1.0
boolean contains(Object entity)
Check if the instance is a managed entity instance belonging to the current persistence context.
Check if the instance is a managed entity instance belonging to the current persistence context.
Parameters:
entity - entity instance
Returns:
boolean indicating if entity is in persistence context
Throws:
IllegalArgumentException - if not an entity
Since:
JPA 1.0
Query createNamedQuery(String name)
Create an instance of Query for executing a named query (in the Java Persistence query language or in native SQL).
Create an instance of Query for executing a named query (in the Java Persistence query language or in native SQL).
Parameters:
name - the name of a query defined in metadata
Returns:
the new query instance
Throws:
IllegalArgumentException - if a query has not been defined with the given name or if the query string is found to be invalid
Since:
JPA 1.0
TypedQuery<T> createNamedQuery(String name, Class<T> resultClass)
Create an instance of TypedQuery for executing a Java Persistence query language named query.
Create an instance of TypedQuery for executing a Java Persistence query language named query. The select list of the query must contain only a single item, which must be assignable to the type specified by the resultClass argument.
Parameters:
name - the name of a query defined in metadata
resultClass - the type of the query result
Returns:
the new query instance
Throws:
IllegalArgumentException - if a query has not been defined with the given name or if the query string is found to be invalid or if the query result is found to not be assignable to the specified type
Since:
JPA 2.0
Query createNativeQuery(String sqlString)
Create an instance of Query for executing a native SQL statement, e.g., for update or delete.
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
Since:
JPA 1.0
Query createNativeQuery(String sqlString, Class resultClass)
Create an instance of Query for executing a native SQL query.
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
Since:
JPA 1.0
Query createNativeQuery(String sqlString, String resultSetMapping)
Create an instance of Query for executing a native SQL query.
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
Since:
JPA 1.0
Query createQuery(String qlString)
Create an instance of Query for executing a Java Persistence query language statement.
Create an instance of Query for executing a Java Persistence query language statement.
Parameters:
qlString - a Java Persistence query string
Returns:
the new query instance
Throws:
IllegalArgumentException - if the query string is found to be invalid
Since:
JPA 1.0
TypedQuery<T> createQuery(String qlString, Class<T> resultClass)
Create an instance of TypedQuery for executing a Java Persistence query language statement.
Create an instance of TypedQuery for executing a Java Persistence query language statement. The select list of the query must contain only a single item, which must be assignable to the type specified by the resultClass argument.
Parameters:
qlString - a Java Persistence query string
resultClass - the type of the query result
Returns:
the new query instance
Throws:
IllegalArgumentException - if the query string is found to be invalid or if the query result is found to not be assignable to the specified type
Since:
JPA 2.0
Create an instance of TypedQuery for executing a criteria query.
Create an instance of TypedQuery for executing a criteria query.
Parameters:
criteriaQuery - a criteria query object
Returns:
the new query instance
Throws:
IllegalArgumentException - if the criteria query is found to be invalid
Since:
JPA 2.0
void detach(Object entity)
Remove the given entity from the persistence context, causing a managed entity to become detached.
Remove the given entity from the persistence context, causing a managed entity to become detached. Unflushed changes made to the entity if any (including removal of the entity), will not be synchronized to the database. Entities which previously referenced the detached entity will continue to reference it.
Parameters:
entity - entity instance
Throws:
IllegalArgumentException - if the instance is not an entity
Since:
JPA 2.0
T find(Class<T> entityClass, Object primaryKey)
Find by primary key.
Find by primary key. Search for an entity of the specified class and primary key. If the entity instance is contained in the persistence context, it is returned from there.
Parameters:
entityClass - entity class
primaryKey - primary key
Returns:
the found entity instance or null if the entity does not exist
Throws:
IllegalArgumentException - if the first argument does not denote an entity type or the second argument is is not a valid type for that entity’s primary key or is null
Since:
JPA 1.0
T find(Class<T> entityClass, Object primaryKey, Map<String,Object> properties)
Find by primary key, using the specified properties.
Find by primary key, using the specified properties. Search for an entity of the specified class and primary key. If the entity instance is contained in the persistence context, it is returned from there. If a vendor-specific property or hint is not recognized, it is silently ignored.
Parameters:
entityClass - entity class
primaryKey - primary key
properties - standard and vendor-specific properties and hints
Returns:
the found entity instance or null if the entity does not exist
Throws:
IllegalArgumentException - if the first argument does not denote an entity type or the second argument is is not a valid type for that entity’s primary key or is null
Since:
JPA 2.0
T find(Class<T> entityClass, Object primaryKey, LockModeType lockMode)
Find by primary key and lock.
Find by primary key and lock. Search for an entity of the specified class and primary key and lock it with respect to the specified lock type. If the entity instance is contained in the persistence context, it is returned from there, and the effect of this method is the same as if the lock method had been called on the entity.

If the entity is found within the persistence context and the lock mode type is pessimistic and the entity has a version attribute, the persistence provider must perform optimistic version checks when obtaining the database lock. If these checks fail, the OptimisticLockException will be thrown.

If the lock mode type is pessimistic and the entity instance is found but cannot be locked:

  • the PessimisticLockException will be thrown if the database locking failure causes transaction-level rollback
  • the LockTimeoutException will be thrown if the database locking failure causes only statement-level rollback

Parameters:
entityClass - entity class
primaryKey - primary key
lockMode - lock mode
Returns:
the found entity instance or null if the entity does not exist
Throws:
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 or is null
TransactionRequiredException - if there is no transaction and a lock mode other than NONE is specified
OptimisticLockException - if the optimistic version check fails
PessimisticLockException - if pessimistic locking fails and the transaction is rolled back
LockTimeoutException - if pessimistic locking fails and only the statement is rolled back
PersistenceException - if an unsupported lock call is made
Since:
JPA 2.0
T find(Class<T> entityClass, Object primaryKey, LockModeType lockMode, Map<String,Object> properties)
Find by primary key and lock, using the specified properties.
Find by primary key and lock, using the specified properties. Search for an entity of the specified class and primary key and lock it with respect to the specified lock type. If the entity instance is contained in the persistence context, it is returned from there.

If the entity is found within the persistence context and the lock mode type is pessimistic and the entity has a version attribute, the persistence provider must perform optimistic version checks when obtaining the database lock. If these checks fail, the OptimisticLockException will be thrown.

If the lock mode type is pessimistic and the entity instance is found but cannot be locked:

  • the PessimisticLockException will be thrown if the database locking failure causes transaction-level rollback
  • the LockTimeoutException will be thrown if the database locking failure causes only statement-level rollback

If a vendor-specific property or hint is not recognized, it is silently ignored.

Portable applications should not rely on the standard timeout hint. Depending on the database in use and the locking mechanisms used by the provider, the hint may or may not be observed.

Parameters:
entityClass - entity class
primaryKey - primary key
lockMode - lock mode
properties - standard and vendor-specific properties and hints
Returns:
the found entity instance or null if the entity does not exist
Throws:
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 or is null
TransactionRequiredException - if there is no transaction and a lock mode other than NONE is specified
OptimisticLockException - if the optimistic version check fails
PessimisticLockException - if pessimistic locking fails and the transaction is rolled back
LockTimeoutException - if pessimistic locking fails and only the statement is rolled back
PersistenceException - if an unsupported lock call is made
Since:
JPA 2.0
void flush()
Synchronize the persistence context to the underlying database.
Synchronize the persistence context to the underlying database.
Throws:
TransactionRequiredException - if there is no transaction
PersistenceException - if the flush fails
Since:
JPA 1.0
Return an instance of CriteriaBuilder for the creation of CriteriaQuery objects.
Return an instance of CriteriaBuilder for the creation of CriteriaQuery objects.
Returns:
CriteriaBuilder instance
Throws:
IllegalStateException - if the entity manager has been closed
Since:
JPA 2.0
Object getDelegate()
Return the underlying provider object for the EntityManager, if available.
Return the underlying provider object for the EntityManager, if available. The result of this method is implementation specific. The unwrap method is to be preferred for new applications.
Returns:
underlying provider object for EntityManager
Since:
JPA 1.0
Return the entity manager factory for the entity manager.
Return the entity manager factory for the entity manager.
Returns:
EntityManagerFactory instance
Throws:
IllegalStateException - if the entity manager has been closed
Since:
JPA 2.0
Get the flush mode that applies to all objects contained in the persistence context.
Get the flush mode that applies to all objects contained in the persistence context.
Returns:
flushMode
Since:
JPA 1.0
LockModeType getLockMode(Object entity)
Get the current lock mode for the entity instance.
Get the current lock mode for the entity instance.
Parameters:
entity - entity instance
Returns:
lock mode
Throws:
TransactionRequiredException - if there is no transaction
IllegalArgumentException - if the instance is not a managed entity and a transaction is active
Since:
JPA 2.0
Return an instance of Metamodel interface for access to the metamodel of the persistence unit.
Return an instance of Metamodel interface for access to the metamodel of the persistence unit.
Returns:
Metamodel instance
Throws:
IllegalStateException - if the entity manager has been closed
Since:
JPA 2.0
Map<String,Object> getProperties()
Get the properties and hints and associated values that are in effect for the entity manager.
Get the properties and hints and associated values that are in effect for the entity manager. Changing the contents of the map does not change the configuration in effect.
Returns:
map of properties and hints in effect for entity manager
Since:
JPA 2.0
T getReference(Class<T> entityClass, Object primaryKey)
Get an instance, whose state may be lazily fetched.
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 - entity class
primaryKey - primary key
Returns:
the found entity instance
Throws:
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 or is null
EntityNotFoundException - if the entity state cannot be accessed
Since:
JPA 1.0
Return the resource-level EntityTransaction object.
Return the resource-level EntityTransaction object. The EntityTransaction instance may be used serially to begin and commit multiple transactions.
Returns:
EntityTransaction instance
Throws:
IllegalStateException - if invoked on a JTA entity manager
Since:
JPA 1.0
boolean isOpen()
Determine whether the entity manager is open.
Determine whether the entity manager is open.
Returns:
true until the entity manager has been closed
Since:
JPA 1.0
Indicate to the entity manager that a JTA transaction is active.
Indicate to the entity manager that a JTA transaction is active. This method should be called on a JTA application managed entity manager that was created outside the scope of the active transaction to associate it with the current JTA transaction.
Throws:
TransactionRequiredException - if there is no transaction
Since:
JPA 1.0
void lock(Object entity, LockModeType lockMode)
Lock an entity instance that is contained in the persistence context with the specified lock mode type.
Lock an entity instance that is contained in the persistence context with the specified lock mode type.

If a pessimistic lock mode type is specified and the entity contains a version attribute, the persistence provider must also perform optimistic version checks when obtaining the database lock. If these checks fail, the OptimisticLockException will be thrown.

If the lock mode type is pessimistic and the entity instance is found but cannot be locked:

  • the PessimisticLockException will be thrown if the database locking failure causes transaction-level rollback
  • the LockTimeoutException will be thrown if the database locking failure causes only statement-level rollback

Parameters:
entity - entity instance
lockMode - lock mode
Throws:
IllegalArgumentException - if the instance is not an entity or is a detached entity
TransactionRequiredException - if there is no transaction
EntityNotFoundException - if the entity does not exist in the database when pessimistic locking is performed
OptimisticLockException - if the optimistic version check fails
PessimisticLockException - if pessimistic locking fails and the transaction is rolled back
LockTimeoutException - if pessimistic locking fails and only the statement is rolled back
PersistenceException - if an unsupported lock call is made
Since:
JPA 1.0
void lock(Object entity, LockModeType lockMode, Map<String,Object> properties)
Lock an entity instance that is contained in the persistence context with the specified lock mode type and with specified properties.
Lock an entity instance that is contained in the persistence context with the specified lock mode type and with specified properties.

If a pessimistic lock mode type is specified and the entity contains a version attribute, the persistence provider must also perform optimistic version checks when obtaining the database lock. If these checks fail, the OptimisticLockException will be thrown.

If the lock mode type is pessimistic and the entity instance is found but cannot be locked:

  • the PessimisticLockException will be thrown if the database locking failure causes transaction-level rollback
  • the LockTimeoutException will be thrown if the database locking failure causes only statement-level rollback

If a vendor-specific property or hint is not recognized, it is silently ignored.

Portable applications should not rely on the standard timeout hint. Depending on the database in use and the locking mechanisms used by the provider, the hint may or may not be observed.

Parameters:
entity - entity instance
lockMode - lock mode
properties - standard and vendor-specific properties and hints
Throws:
IllegalArgumentException - if the instance is not an entity or is a detached entity
TransactionRequiredException - if there is no transaction
EntityNotFoundException - if the entity does not exist in the database when pessimistic locking is performed
OptimisticLockException - if the optimistic version check fails
PessimisticLockException - if pessimistic locking fails and the transaction is rolled back
LockTimeoutException - if pessimistic locking fails and only the statement is rolled back
PersistenceException - if an unsupported lock call is made
Since:
JPA 2.0
T merge(T entity)
Merge the state of the given entity into the current persistence context.
Merge the state of the given entity into the current persistence context.
Parameters:
entity - entity instance
Returns:
the managed instance that the state was merged to
Throws:
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
Since:
JPA 1.0
void persist(Object entity)
Make an instance managed and persistent.
Make an instance managed and persistent.
Parameters:
entity - entity instance
Throws:
EntityExistsException - if the entity already exists. (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 flush or commit time.)
IllegalArgumentException - if the instance is not an entity
TransactionRequiredException - if invoked on a container-managed entity manager of type PersistenceContextType.TRANSACTION and there is no transaction
Since:
JPA 1.0
void refresh(Object entity)
Refresh the state of the instance from the database, overwriting changes made to the entity, if any.
Refresh the state of the instance from the database, overwriting changes made to the entity, if any.
Parameters:
entity - entity instance
Throws:
IllegalArgumentException - if the instance is not an entity or the 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
Since:
JPA 1.0
void refresh(Object entity, Map<String,Object> properties)
Refresh the state of the instance from the database, using the specified properties, and overwriting changes made to the entity, if any.
Refresh the state of the instance from the database, using the specified properties, and overwriting changes made to the entity, if any.

If a vendor-specific property or hint is not recognized, it is silently ignored.

Parameters:
entity - entity instance
properties - standard and vendor-specific properties and hints
Throws:
IllegalArgumentException - if the instance is not an entity or the 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
Since:
JPA 2.0
void refresh(Object entity, LockModeType lockMode)
Refresh the state of the instance from the database, overwriting changes made to the entity, if any, and lock it with respect to given lock mode type.
Refresh the state of the instance from the database, overwriting changes made to the entity, if any, and lock it with respect to given lock mode type.

If the lock mode type is pessimistic and the entity instance is found but cannot be locked:

  • the PessimisticLockException will be thrown if the database locking failure causes transaction-level rollback
  • the LockTimeoutException will be thrown if the database locking failure causes only statement-level rollback.

Parameters:
entity - entity instance
lockMode - lock mode
Throws:
IllegalArgumentException - if the instance is not an entity or the entity is not managed
TransactionRequiredException - if there is no transaction and if invoked on a container-managed EntityManager instance with PersistenceContextType.TRANSACTION or with a lock mode other than NONE
EntityNotFoundException - if the entity no longer exists in the database
PessimisticLockException - if pessimistic locking fails and the transaction is rolled back
LockTimeoutException - if pessimistic locking fails and only the statement is rolled back
PersistenceException - if an unsupported lock call is made
Since:
JPA 2.0
void refresh(Object entity, LockModeType lockMode, Map<String,Object> properties)
Refresh the state of the instance from the database, overwriting changes made to the entity, if any, and lock it with respect to given lock mode type and with specified properties.
Refresh the state of the instance from the database, overwriting changes made to the entity, if any, and lock it with respect to given lock mode type and with specified properties.

If the lock mode type is pessimistic and the entity instance is found but cannot be locked:

  • the PessimisticLockException will be thrown if the database locking failure causes transaction-level rollback
  • the LockTimeoutException will be thrown if the database locking failure causes only statement-level rollback

If a vendor-specific property or hint is not recognized, it is silently ignored.

Portable applications should not rely on the standard timeout hint. Depending on the database in use and the locking mechanisms used by the provider, the hint may or may not be observed.

Parameters:
entity - entity instance
lockMode - lock mode
properties - standard and vendor-specific properties and hints
Throws:
IllegalArgumentException - if the instance is not an entity or the entity is not managed
TransactionRequiredException - if there is no transaction and if invoked on a container-managed EntityManager instance with PersistenceContextType.TRANSACTION or with a lock mode other than NONE
EntityNotFoundException - if the entity no longer exists in the database
PessimisticLockException - if pessimistic locking fails and the transaction is rolled back
LockTimeoutException - if pessimistic locking fails and only the statement is rolled back
PersistenceException - if an unsupported lock call is made
Since:
JPA 2.0
void remove(Object entity)
Remove the entity instance.
Remove the entity instance.
Parameters:
entity - entity instance
Throws:
IllegalArgumentException - if the instance is not an entity or is a detached entity
TransactionRequiredException - if invoked on a container-managed entity manager of type PersistenceContextType.TRANSACTION and there is no transaction
Since:
JPA 1.0
void setFlushMode(FlushModeType flushMode)
Set the flush mode that applies to all objects contained in the persistence context.
Set the flush mode that applies to all objects contained in the persistence context.
Parameters:
flushMode - flush mode
Since:
JPA 1.0
void setProperty(String propertyName, Object value)
Set an entity manager property or hint.
Set an entity manager property or hint. If a vendor-specific property or hint is not recognized, it is silently ignored.
Parameters:
propertyName - name of property or hint
value - value for property or hint
Throws:
IllegalArgumentException - if the second argument is not valid for the implementation
Since:
JPA 2.0
T unwrap(Class<T> cls)
Return an object of the specified type to allow access to the provider-specific API.
Return an object of the specified type to allow access to the provider-specific API. If the provider's EntityManager implementation does not support the specified class, the PersistenceException is thrown.
Parameters:
cls - the class of the object to be returned. This is normally either the underlying EntityManager implementation class or an interface that it implements.
Returns:
an instance of the specified class
Throws:
PersistenceException - if the provider does not support the call
Since:
JPA 2.0

This documentation page is derived (with some adjustments) from the open source JPA 2 RI (EclipseLink)
and is available under the terms of the Eclipse Public License, v. 1.0 and Eclipse Distribution License, v. 1.0.
Object Relational Mapping (ORM) JPA 2 providers include Hibernate, EclipseLink, TopLink, OpenJPA and DataNucleus.
Object DB is not an ORM JPA implementation but an Object Database for Java with built in JPA 2 support.