EntityManager (Java EE 5 SDK)

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javax.persistence Interface EntityManager

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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.

从以下版本开始:

Java Persistence 1.0

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方法摘要
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 the Java Persistence query language or in 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 qlString)           Create an instance of Query for executing a Java Persistence query language 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. getReference(Class<T> entityClass, Object primaryKey)
          Get an instance, whose state may be lazily fetched.  EntityTransaction getTransaction()
          Returns 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. 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.  

方法详细信息

persist

void persist(Object entity)

Make an entity instance managed and persistent.

参数:

entity -

抛出异常:

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 flush or 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.

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merge

<T> T merge(T entity)

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

参数:

entity -

返回:

the instance that the state was merged to

抛出异常:

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.

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remove

void remove(Object entity)

Remove the entity instance.

参数:

entity -

抛出异常:

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.

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find

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

Find by primary key.

参数:

entityClass -

primaryKey -

返回:

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

抛出异常:

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

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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, throws EntityNotFoundException when the instance state is first accessed. (The persistence provider runtime is permitted to throw EntityNotFoundException when getReference(java.lang.Class, java.lang.Object) 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.

参数:

entityClass -

primaryKey -

返回:

the found entity instance

抛出异常:

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

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flush

void flush()

Synchronize the persistence context to the underlying database.

抛出异常:

IllegalStateException - if this EntityManager has been closed.

TransactionRequiredException - if there is no transaction

PersistenceException - if the flush fails

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setFlushMode

void setFlushMode(FlushModeType flushMode)

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

参数:

flushMode -

抛出异常:

IllegalStateException - if this EntityManager has been closed.

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getFlushMode

FlushModeType getFlushMode()

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

返回:

flush mode

抛出异常:

IllegalStateException - if this EntityManager has been closed.

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lock

void lock(Object entity,
          LockModeType lockMode)

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

参数:

entity -

lockMode -

抛出异常:

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

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refresh

void refresh(Object entity)

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

参数:

entity -

抛出异常:

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.

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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.

抛出异常:

IllegalStateException - if this EntityManager has been closed.

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contains

boolean contains(Object entity)

Check if the instance belongs to the current persistence context.

参数:

entity -

返回:

true if the instance belongs to the current persistence context.

抛出异常:

IllegalStateException - if this EntityManager has been closed.

IllegalArgumentException - if not an entity

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createQuery

Query createQuery(String qlString)

Create an instance of Query for executing a Java Persistence query language statement.

参数:

qlString - a Java Persistence query language query string

返回:

the new query instance

抛出异常:

IllegalStateException - if this EntityManager has been closed.

IllegalArgumentException - if query string is not valid

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createNamedQuery

Query createNamedQuery(String name)

Create an instance of Query for executing a named query (in the Java Persistence query language or in native SQL).

参数:

name - the name of a query defined in metadata

返回:

the new query instance

抛出异常:

IllegalStateException - if this EntityManager has been closed.

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

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createNativeQuery

Query createNativeQuery(String sqlString)

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

参数:

sqlString - a native SQL query string

返回:

the new query instance

抛出异常:

IllegalStateException - if this EntityManager has been closed.

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createNativeQuery

Query createNativeQuery(String sqlString,
                        Class resultClass)

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

参数:

sqlString - a native SQL query string

resultClass - the class of the resulting instance(s)

返回:

the new query instance

抛出异常:

IllegalStateException - if this EntityManager has been closed.

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createNativeQuery

Query createNativeQuery(String sqlString,
                        String resultSetMapping)

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

参数:

sqlString - a native SQL query string

resultSetMapping - the name of the result set mapping

返回:

the new query instance

抛出异常:

IllegalStateException - if this EntityManager has been closed.

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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.

抛出异常:

IllegalStateException - if this EntityManager has been closed.

TransactionRequiredException - if there is no transaction.

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getDelegate

Object getDelegate()

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

抛出异常:

IllegalStateException - if this EntityManager has been closed.

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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.

抛出异常:

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

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isOpen

boolean isOpen()

Determine whether the EntityManager is open.

返回:

true until the EntityManager has been closed.

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getTransaction

EntityTransaction getTransaction()

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

返回:

EntityTransaction instance

抛出异常:

IllegalStateException - if invoked on a JTA EntityManager.

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概述  软件包   类  树  已过时  索引  帮助		Java EE 5 SDK 深圳电信培训中心.徐海蛟老师.
上一个类   下一个类	框架    无框架
摘要: 嵌套 | 字段 | 构造器 | 方法	详细信息: 字段 | 构造器 | 方法

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