Enterprise JavaBeans 3.1, 6th Edition

Managed Versus Unmanaged Entities

Before we can go any deeper into the entity manager service, we need to delve more deeply into the lifecycle of entity object instances. An entity bean instance is either managed (aka attached) by an entity manager or unmanaged (aka detached). When an entity is attached to an EntityManager, the manager tracks state changes to the entity and synchronizes those changes to the database whenever the entity manager decides to flush its state. When an entity is detached, it is unmanaged. Any state changes to an entity that is detached are not tracked by the entity manager.

Persistence Context

A persistence context is a set of managed entity object instances. Persistence contexts are managed by an entity manager. The entity manager tracks all entity objects within a persistence context for changes and updates made, and flushes these changes to the database using the flush mode rules discussed later in this chapter. Once a persistence context is closed, all managed entity object instances become detached and are no longer managed. Once an object is detached from a persistence context, it can no longer be managed by an entity manager, and any state changes to this object instance will not be synchronized with the database.

Note

When a persistence context is closed, all managed entity objects become detached and are unmanaged.

There are two types of persistence contexts: transaction-scoped and extended persistence contexts.

Transaction-scoped persistence context ...