Getting started with JPA and Mule

Working with JPA managed entities in Mule applications can be difficult.  Since the JPA session is not propagated between message processors, transformers are typically needed to produce an entity from a message’s payload, pass it to a component for processing, then serialize it back to an un-proxied representation for further processing.

Transactions have been complicated too.  Its difficult to coordinate a transaction between multiple components that are operating with JPA entity payloads.  Finally the lack of support for JPA queries makes it difficult to  load objects without working with raw SQL and the JDBC transport.

Mule Support for JPA Entities

The JPA module aims to simplify working with JPA managed entities with Mule.  It provides message processors that map to an EntityManager’s methods.  The message processors participate in Mule transactions, making it easy to structure JPA transactions within Mule flows.  The JPA module also provides a @PersistenceContext implementation.  This allows Mule components to participate in JPA transactions.

Installing the JPA Module

To install the JPA Module you need to click on “Help” followed by “Install New Software…” from Mule Studio.  Select the “MuleStudio Cloud Connectors Update Site” from the “Work With” drop-down list then find the “Mule Java Persistence API Module Mule Extension.”  This is illustrated below:

Fetching JPA Entities

JPA query language or criteria queries can be executed using the “query” MP.  Supplying a statement to the query will execute the given query and return the results to the next message processor, as illustrated in the following Gist:

<flow name="testQueryWithListParameters">
  <jpa:query statement="from Dog dog where dog.name = ?" queryParameters-ref="#[payload:]"/>
  <vm:outbound-endpoint path="foo"/>
</flow>

<flow name="testQueryWithMapParameters">
   <jpa:query statement="from Dog dog where dog.name = :name and dog.breed = :breed" queryParameters-ref="#[payload:]"/>
</flow>

CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Dog> criteriaQuery = criteriaBuilder.createQuery(Dog.class);
Root<Dog> from = criteriaQuery.from(Dog.class);
 
Predicate condition = criteriaBuilder.equal(from.get("name"), "Cujo");
criteriaQuery.where(condition);
 
runFlowWithPayloadAndExpect("testQuery", expectedResults, criteriaQuery);

<flow name="testFind">
  <jpa:find entityClass="domain.Dog" id-ref="#[payload:]"/>
</flow>

<flow name="testTransactionalInsertAndQuery">
    <transactional>
        <jpa:persist/>
        <jpa:query statement="from Dog dog where dog.name = 'Cujo'"/>
    </transactional>
</flow>

<flow name="testMerge">
     <vm:inbound-endpoint path="in"/>
     <transactional>
        <jpa:merge/>
        ....other processing here....
    </transactional>
    <vm:outbound-endpoint path="foo"/>
</flow>

 <flow name="testDetach">
    <transactional>
        <jpa:detach/>
    </transactional>
</flow>

public class DogServiceImpl {

    @PersistenceContext
    EntityManager entityManager;

    public Dog groom(Dog dog) {
        return entityManager.merge(dog);
    }
    
}

<flow name="dogGroomingFlow">
    <vm:inbound-endpoint path="dog.groom.in"/>
    <transactional>
        <jpa:merge/>
        <component class="service.DogServiceImpl"/>
     </transactional>
     <vm:outbound-endpoint path="dog.groom.out"/>
</flow>