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Manual
61

Database Connection using JPA

A connection to a database is represented by an EntityManager instance, which also provides ... database connection, using a separate EntityManager instance, for every HTTP request. The main role of an EntityManagerFactory instance is to support instantiation of EntityManager instances
Manual
56

Detached Entity Objects

EntityManager but still represent objects in the database. Compared to managed entity objects, detached ... the database unless modified detached objects are merged back into an EntityManager to become managed again. Detached objects are useful in situations in which an EntityManager is not available
Manual
53

Retrieving JPA Entity Objects

. Given an EntityManager em, the following code fragment demonstrates retrieval of an Employee object ... if the specified class is not an entity class. If the EntityManager already manages the specified entity ... except that if the entity object is not already managed by the EntityManager a hollow object
JPA Doc
50

javax.persistence.EntityManager

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 ... . The EntityManager API is used to create and remove persistent entity instances, to find entities by their primary
JPA Doc
45

getDelegate()

Method javax.persistence.EntityManager Object getDelegate() 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
JPA Doc
45

unwrap(cls)

Method javax.persistence.EntityManager T unwrap(   Class cls ) Return an object of the specified type to allow access to the provider-specific API. If the provider's EntityManager implementation ... of the object to be returned. This is normally either the underlying EntityManager implementation
JPA Doc
45

close()

Method javax.persistence.EntityManager void close() 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
JPA Doc
45

refresh(entity, lockMode)

Method javax.persistence.EntityManager void refresh(   Object entity,   LockModeType lockMode ) Refresh the state of the instance from the database, overwriting changes made to the entity, if any ... on a container-managed EntityManager instance with PersistenceContextType.TRANSACTION or with a lock mode
JPA Doc
45

refresh(entity, lockMode, properties)

Method javax.persistence.EntityManager void refresh(   Object entity,   LockModeType lockMode,   Map properties ) Refresh the state of the instance from the database, overwriting ... -managed EntityManager instance with PersistenceContextType.TRANSACTION or with a lock mode
Tutorial
44

Step 3: Define a Spring DAO Component

; import javax.persistence.EntityManager; import javax.persistence.PersistenceContext; import javax ... connection: @PersistenceContext private EntityManager em; // Stores a new guest ... the controller, as shown in the next step. Prepares an EntityManager automatically and injects it into the em