# JPA

## JPA Component

The jpa component enables you to store and retrieve Java objects from persistent storage using EJB 3's Java Persistence Architecture (JPA), which is a standard interface layer that wraps Object/Relational Mapping (ORM) products such as OpenJPA, Hibernate, TopLink, and so on.

## Sending to the endpoint

You can store a Java entity bean in a database by sending it to a JPA producer endpoint. The body of the In message is assumed to be an entity bean (that is, a POJO with an @Entity annotation on it) or a collection or an array of entity beans.

If the body does not contain one of the preceding types, put a Message TranslatorMessage Translator in front of the endpoint to perform the necessary conversion first.

## Consuming from the endpoint

Consuming messages from a JPA consumer endpoint removes (or updates) entity beans in the database. This allows you to use a database table as a logical queue: consumers take messages from the queue and then delete/update them to logically remove them from the queue.

If you do not wish to delete the entity bean when it has been processed, you can specify `consumeDelete=false` on the URI. This will result in the entity being processed each poll.

If you would rather perform some update on the entity to mark it as processed (such as to exclude it from a future query) then you can annotate a method with @Consumed which will be invoked on your entity bean when the entity bean is consumed.

## URI format

    jpa:[entityClassName][?options]

For sending to the endpoint, the entityClassName is optional. If specified, it helps the Type Converter to ensure the body is of the correct type.

For consuming, the entityClassName is mandatory.

You can append query options to the URI in the following format, `?option=value&option=value&...`

## Options

Table 55, “URI options” lists the JPA uri options:

Table 55. URI options

Name | Default Value | Description
--- | --- | ---
`entityType` | entityClassName | Overrides the entityClassName from the URI.
`persistenceUnit` | `camel` | The JPA persistence unit used by default.
`consumeDelete` | `true` | JPA consumer only: If `true`, the entity is deleted after it is consumed; if `false`, the entity is not deleted.
`consumeLockEntity` | `true` | JPA consumer only: Specifies whether or not to set an exclusive lock on each entity bean while processing the results from polling.
`flushOnSend` | `true` | JPA producer only: Flushes the EntityManager after the entity bean has been persisted.
`maximumResults` | `-1` | JPA consumer only: Set the maximum number of results to retrieve on the Query.
`transactionManager` | `null` | Apache Camel 1.6.1/2.0: Specifies the transaction manager to use. If none provided, Apache Camel will use a `JpaTransactionManager` by default. Can be used to set a JTA transaction manager (for integration with an EJB container).
`consumer.delay` | `500` | JPA consumer only: Delay in milliseconds between each poll.
`consumer.initialDelay` | `1000` | JPA consumer only: Milliseconds before polling starts.
`consumer.useFixedDelay` | `false` | JPA consumer only: Set to `true` to use fixed delay between polls, otherwise fixed rate is used. See ScheduledExecutorService in JDK for details.
`maxMessagesPerPoll` | `0` | Apache Camel 2.0: JPA consumer only: An integer value to define the maximum number of messages to gather per poll. By default, no maximum is set. Can be used to avoid polling many thousands of messages when starting up the server. Set a value of 0 or negative to disable.
`consumer.query` |  | JPA consumer only: To use a custom query when consuming data.
`consumer.resultClass` |  | Apache Camel 2.7: JPA consumer only: Defines the type of the returned payload (we will call `entityManager.createNativeQuery(nativeQuery, resultClass)` instead of `entityManager.createNativeQuery(nativeQuery)`). Without this option, we will return an object array. Only has an affect when using in conjunction with native query when consuming data.
`consumer.namedQuery` |  | JPA consumer only: To use a named query when consuming data.
`consumer.nativeQuery` |  | JPA consumer only: To use a custom native query when consuming data.
`usePersist` | `false` | Apache Camel 2.5: JPA producer only: Indicates to use `entityManager.persist(entity)` instead of `entityManager.merge(entity)`. Note: `entityManager.persist(entity)` doesn't work for detached entities (where the EntityManager has to execute an UPDATE instead of an INSERT query)!

## Message Headers

Apache Camel adds the following message header to the exchange:

Table 56. Message header options

Header | Type | Description
--- | --- | ---
`CamelJpaTemplate` | `JpaTemplate` | Apache Camel 2.0: The `JpaTemplate` object that is used to access the entity bean. You need this object in some situations, for instance in a type converter or when you are doing some custom processing.

## Configuring EntityManagerFactory

You are strongly advised to configure the JPA component to use a specific `EntityManagerFactory` instance. If you do not do so, each `JpaEndpoint` will auto-create its own `EntityManagerFactory` instance.For example, you can instantiate a JPA component that references the `myEMFactory` entity manager factory, as follows:

    <bean id="jpa" class="org.apache.camel.component.jpa.JpaComponent">
       <property name="entityManagerFactory" ref="myEMFactory"/>
    </bean>

In Apache Camel 2.3 the `JpaComponent` will auto lookup the `EntityManagerFactory` from the Registry which means you do not need to configure this on the `JpaComponent` as shown above. You only need to do so if there is ambiguity, in which case Camel will log a WARN.

## Configuring TransactionManager

You are strongly advised to specify the `TransactionManager` instance used by the JPA component. If you do not do so, each `JpaEndpoint` will auto-create its own instance of `TransactionManager`. For example, you can instantiate a JPA component that references the `myTransactionManager` transaction manager, as follows:

    <bean id="jpa" class="org.apache.camel.component.jpa.JpaComponent">
       <property name="entityManagerFactory" ref="myEMFactory"/>
       <property name="transactionManager" ref="myTransactionManager"/>
    </bean>

In Apache Camel 2.3 the `JpaComponent` will auto lookup the `TransactionManager` from the Registry which means you do not need to configure this on the `JpaComponent` as shown above. You only need to do so if there is ambiguity, in which case Camel will log a WARN.

## Using a consumer with a named query

For consuming only selected entities, you can use the `consumer.namedQuery` URI query option. First, you have to define the named query in the JPA Entity class:

    @Entity
    @NamedQuery(name = "step1", query = "select x from MultiSteps x where x.step = 1")
    public class MultiSteps {
       ...
    }

After that you can define a consumer uri like this one:

    from("jpa://org.apache.camel.examples.MultiSteps?consumer.namedQuery=step1")
    .to("bean:myBusinessLogic");

## Using a consumer with a query

For consuming only selected entities, you can use the `consumer.query` URI query option. You only have to define the query option:

    from("jpa://org.apache.camel.examples.MultiSteps?consumer.query=select o from org.apache.camel.examples.MultiSteps o where o.step = 1")
    .to("bean:myBusinessLogic");

## Using a consumer with a native query

For consuming only selected entities, you can use the `consumer.nativeQuery` URI query option. You only have to define the native query option:

    from("jpa://org.apache.camel.examples.MultiSteps?consumer.nativeQuery=select * from MultiSteps where step = 1")
    .to("bean:myBusinessLogic");

If you use the native query option, you will receive an object array in the message body.

## Example

See the Tracer Example for an example using JPA to store traced messages into a database.