--- title: Entity Providers order: 5 layout: page --- [[jpacontainer.entityprovider]] = Entity Providers Entity providers provide access to entities persisted in a data store. They are essentially wrappers over a JPA entity manager, adding optimizations and other features important when binding persistent data to a user interface. The choice and use of entity providers is largely invisible if you create your [classname]#JPAContainer# instances with the [classname]#JPAContainerFactory#, which hides such details. JPAContainer entity providers can be customized, which is necessary for some purposes. Entity providers can be Enterprise JavaBeans (EJBs), which is useful when you use them in a Java EE application server. [[jpacontainer.entityprovider.built-in]] == Built-In Entity Providers JPAContainer includes various kinds of built-in entity providers: caching and non-caching, read-write and read-only, and batchable. __Caching__ is useful for performance, but takes some memory for the cache and makes the provider stateful. __Batching__, that is, running updates in larger batches, can also enhance performance and be used together with caching. It is stateless, but doing updates is a bit more complex than otherwise. Using a __read-only__ container is preferable if read-write capability is not needed. All built-in providers are __local__ in the sense that they provide access to entities using a local JPA entity manager. The [classname]#CachingMutableLocalEntityProvider# is usually recommended as the first choise for read-write access and [classname]#CachingLocalEntityProvider# for read-only access. === [classname]#LocalEntityProvider# A read-only, lazy loading entity provider that does not perform caching and reads its data directly from an entity manager. You can create the provider with [methodname]#makeNonCachedReadOnly()# method in [classname]#JPAContainerFactory#. === [classname]#MutableLocalEntityProvider# Extends [classname]#LocalEntityProvider# with write support. All changes are directly sent to the entity manager. Transactions can be handled either internally by the provider, which is the default, or by the container. In the latter case, you can extend the class and annotate it, for example, as described in <>. The provider can notify about updates to entities through the [interfacename]#EntityProviderChangeNotifier# interface. === [classname]#BatchableLocalEntityProvider# A simple non-caching implementation of the [interfacename]#BatchableEntityProvider# interface. It extends [classname]#MutableLocalEntityProvider# and simply passes itself to the [methodname]#batchUpdate()# callback method. This will work properly if the entities do not contain any references to other entities that are managed by the same container. === [classname]#CachingLocalEntityProvider# A read-only, lazy loading entity provider that caches both entities and query results for different filter/sortBy combinations. When the cache gets full, the oldest entries in the cache are removed. The maximum number of entities and entity IDs to cache for each filter/sortBy combination can be configured in the provider. The cache can also be manually flushed. When the cache grows full, the oldest items are removed. You can create the provider with [methodname]#makeReadOnly()# method in [classname]#JPAContainerFactory#. === [classname]#CachingMutableLocalEntityProvider# Just like [classname]#CachingLocalEntityProvider#, but with read-write access. For read access, caching works just like in the read-only provider. When an entity is added or updated, the cache is flushed in order to make sure the added or updated entity shows up correctly when using filters and/or sorting. When an entity is removed, only the filter/sortBy-caches that actually contain the item are flushed. This is perhaps the most commonly entity provider that you should consider using for most tasks. You can create it with the [methodname]#make()# method in [classname]#JPAContainerFactory#. === [classname]#CachingBatchableLocalEntityProvider# This provider supports making updates in __batches__. You need to implement a [interfacename]#BatchUpdateCallback# that does all the updates and execute the batch by calling [methodname]#batchUpdate()# on the provider. The provider is an extension of the [classname]#CachingMutableLocalEntityProvider# that implements the [interfacename]#BatchableEntityProvider# interface. This will work properly if the entities do not contain any references to other entities that are managed by the same container. You can create the provider with [methodname]#makeBatchable()# method in [classname]#JPAContainerFactory#. [[jpacontainer.entityprovider.jndi]] == Using JNDI Entity Providers in JEE6 Environment JPAContainer 2.0 introduced a new set of entity providers specifically for working in a [literal]#++JEE6++# environment. In a JEE environment, you should use an entity manager provided by the application server and, usually, [literal]#++JTA++# transactions instead of transactions provided by JPA. Entity providers in [package]#com.vaadin.addon.jpacontainer.provider.jndijta# package work mostly the same way as the normal providers discussed earlier, but use JNDI lookups to get reference to an [interfacename]#EntityManager# and to a JTA transaction. The JNDI providers work with almost no special configuration at all. The [classname]#JPAContainerFactory# has factory methods for creating various JNDI provider types. The only thing that you commonly need to do is to expose the [interfacename]#EntityManager# to a JNDI address. By default, the JNDI providers look for the [interfacename]#EntityManager# from " java:comp/env/persistence/em". This can be done with the following snippet in [filename]#web.xml# or with similar configuration with annotations. ---- persistence/em MYPU ---- The " [literal]#++MYPU++#" is the identifier of your persistence unit defined in your [filename]#persistence.xml# file. If you choose to annotate your servlets (instead of using the [filename]#web.xml# file as described above), you can simply add the following annotation to your servlet. ---- @PersistenceContext(name="persistence/em",unitName="MYPU") ---- If you wish to use another address for the persistence context, you can define them with the [methodname]#setJndiAddresses()# method. You can also define the location for the JTA [classname]#UserTransaction#, but that should be always accessible from " java:comp/UserTransaction" by the JEE6 specification. [[jpacontainer.entityprovider.ejb]] == Entity Providers as Enterprise Beans Entity providers can be Enterprise JavaBeans (EJB). This may be useful if you use JPAContainer in a Java EE application server. In such case, you need to implement a custom entity provider that allows the server to inject the entity manager. For example, if you need to use Java Transaction API (JTA) for JPA transactions, you can implement such entity provider as follows. Just extend a built-in entity provider of your choise and annotate the entity manager member as [literal]#++@PersistenceContext++#. Entity providers can be either stateless or stateful session beans. If you extend a caching entity provider, it has to be stateful. ---- @Stateless @TransactionManagement public class MyEntityProviderBean extends MutableLocalEntityProvider { @PersistenceContext private EntityManager em; protected LocalEntityProviderBean() { super(MyEntity.class); setTransactionsHandledByProvider(false); } @Override @TransactionAttribute(TransactionAttributeType.REQUIRED) protected void runInTransaction(Runnable operation) { super.runInTransaction(operation); } @PostConstruct public void init() { setEntityManager(em); /* * The entity manager is transaction-scoped, which means * that the entities will be automatically detached when * the transaction is closed. Therefore, we do not need * to explicitly detach them. */ setEntitiesDetached(false); } } ---- If you have more than one EJB provider, you might want to create an abstract super class of the above and only define the entity type in implementations. You can implement an entity provider as a managed bean in Spring Framefork the same way.