how to attach entity in JAX-RS service?

[Rj Ewing]

am validating and uploading data in my webapp. In this process, I need to get user input, so the validating and uploading is split between 2 requests. In the 1st request I setup/fetch all the information and then save it in the session. This includes a Entity object that I later access in the 2nd request.

My question is how do I reattach the entity in the 2nd request so I don't get a LazyInitializationException? I have tried the following:

 // we need to reattach the entities to the jpa session to avoid lazy-initialization exceptions
    EntityManager manager = jpaContext.getEntityManagerByManagedType(myEntity.class);
    manager.merge(myEntity);

I am getting the error: javax.persistence.TransactionRequiredException: No EntityManager with actual transaction available for current thread - cannot reliably process 'merge' call, even though I have the annotated the method with Spring's @Transactional.

I am able to get this to work with the following code, however it is hibernate specific and I would rather it not.

EntityManager manager = managerFactory.createEntityManager();
Session hibernateSession = manager.unwrap(Session.class);
try {
    hibernateSession.update(myEntity);
    // more code
finally {
    hibernateSession.close();
}  

Any ideas on how to improve this would be helpful. I also realize that we should be using HttpSessions for REST calls, but this is legacy code and that's how it is done for now.
These request method are Jersey REST service calls if that makes a difference. The jpa code lives in a commons jar file and this service is in the project that uses the commons jar.

[Frits Walraven]

I am getting the error: javax.persistence.TransactionRequiredException: No EntityManager with actual transaction available for current thread - cannot reliably process 'merge' call, even though I have the annotated the method with Spring's @Transactional.

How did you configure JPA in Spring?

You might find this link spring-hibernate-jpa useful.

[Rj Ewing]

I'll take a look at the link. For now here is my config xml:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Repository and Service Layers-->

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:jpa="http://www.springframework.org/schema/data/jpa"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
       http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
       http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
       http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa.xsd ">

    <context:property-placeholder location="classpath:biocode-fims-database.properties" />

    <bean id="dataSource"
          class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="${Class}" />
        <property name="url" value="${Url}" />
        <property name="username" value="${User}" />
        <property name="password" value="${Password}" />
    </bean>

    <bean id="jpaVendorAdapter" class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
    </bean>

    <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <property name="jpaVendorAdapter" ref="jpaVendorAdapter"/>
        <property name="packagesToScan" value="biocode.fims.entities"/>
        <property name="jpaProperties">
            <props>
                <!--<prop key="hibernate.hbm2ddl.auto">validate</prop>-->
                <prop key="hibernate.dialect">org.hibernate.dialect.MySQL5InnoDBDialect</prop>
                <prop key="hibernate.show_sql">${hibernate.show_sql}</prop>
                <prop key="hibernate.format_sql">${hibernate.format_sql}</prop>
                <prop key="hibernate.id.new_generator_mappings">true</prop>
                <prop key="hibernate.max_fetch_depth">3</prop>
            </props>
        </property>
    </bean>

    <!-- Enables the Hibernate @Transactional programming model -->
    <tx:annotation-driven transaction-manager="transactionManager" />

    <bean id="transactionManager"
          class="org.springframework.orm.jpa.JpaTransactionManager">
    </bean>

    <bean id="persistenceExceptionTranslationPostProcessor" class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/>

    <jpa:repositories base-package="biocode.fims.repositories" />
</beans>

[Frits Walraven]

Just had a quick glance at you configuration.

The difference between the two configurations is in the declaration of the TransactionManager. You might want to change yours according to the one given in the link.

[Rj Ewing]

So I tried the changing the TransactionManager config as shown in the link with no luck. I still have the same exception being thrown. Here's the jersey class to provide more context.

@Transactional
@Path("validate")
public class Validate {

    private EntityManagerFactory managerFactory;
    private JpaContext jpaContext;

    @Autowired
    Validate(JpaContext jpaContext, EntityManagerFactory managerFactory) {
        this.jpaContext = jpaContext;
        this.managerFactory = managerFactory;
    }


    @POST
    @Consumes(MediaType.MULTIPART_FORM_DATA)
    @Produces(MediaType.APPLICATION_JSON + ";charset=utf-8")
    public String validate(@FormDataParam("projectId") Integer projectId,
                            // other params) {
       // validate the provided file.
       // Save myEntity to the httpsession
    }

    @GET
    @Path("/continue")
    @Produces(MediaType.APPLICATION_JSON + ";charset=utf-8")
    public String upload() {
        // get myEntity from the httpsession

        // we need to reattach the entities to the jpa session to avoid lazy-initialization exceptions
        EntityManager manager = jpaContext.getEntityManagerByManagedType(myEntity.class);
        manager.merge(myEntity);

        // do some work with myEntity.myLazyCollection()
        //upload the file
    }
}

[Roel De Nijs]

Is there any reason why you don't inject the EntityManager like this? Then you could use em in the upload() method. More info about how the Spring @Transactional annotation works, can be found in this article.

@PersistenceContext
private EntityManager em;

Hope it helps!
Kind regards,
Roel

[Rj Ewing]

Roel De Nijs wrote:Is there any reason why you don't inject the EntityManager like this? Then you could use em in the upload() method. More info about how the Spring @Transactional annotation works, can be found in this article.

@PersistenceContext
private EntityManager em;

Hope it helps!
Kind regards,
Roel

When I inject the EntityManager like that, it is null. I'll take a look at the link. Thanks

[Roel De Nijs]

Rj Ewing wrote:When I inject the EntityManager like that, it is null. I'll take a look at the link. Thanks

You could try the following instead

@Autowired
Validate(JpaContext jpaContext, EntityManagerFactory managerFactory) {
  this.em = managerFactory.createEntityManager();
}

[Rj Ewing]

Roel De Nijs wrote:

Rj Ewing wrote:When I inject the EntityManager like that, it is null. I'll take a look at the link. Thanks

You could try the following instead

@Autowired
Validate(JpaContext jpaContext, EntityManagerFactory managerFactory) {
  this.em = managerFactory.createEntityManager();
}

That is essentially what I am doing, just in upload() and not the constructor. I get a lazyinitializationException if I try:

EntityManager manager = managerFactory.createEntityManager();
manager.merge(myEntity);
myEntity.getLazilyLoadedData();

[Roel De Nijs]

Rj Ewing wrote:That is essentially what I am doing, just in upload() and not the constructor.

And what happens if you create the entity manager in the constructor?

[Rj Ewing]

Roel De Nijs wrote:

Rj Ewing wrote:That is essentially what I am doing, just in upload() and not the constructor.

And what happens if you create the entity manager in the constructor?

I still get a LazyInitializationException

[Roel De Nijs]

Rj Ewing wrote:I still get a LazyInitializationException

Does this happen on the merge() call or on the getLazilyLoadedData() one?

[Rj Ewing]

the getLazilyLoadedData() call

[Roel De Nijs]

Rj Ewing wrote:the getLazilyLoadedData() call

And I assume the lazy loaded data was not yet loaded in the entity you have added on the session. Based on this article, that seems to be the expected behavior of the merge() method. A merge() consists of:

retrieve the entity with the same ID as the detached one passed as argument,

copy the state of the detached entity to the attached one,

and return the attached entity.

So you'll probably need to do update your entity model and cascade merging using the cascade attribute of the relationship annotation e.g. @OneToOne). Something like

@Entity
class Project {
    @OneToOne(cascade=CascadeType.MERGE)
    private Manager manager;
}

More info provided in this article.

[Rj Ewing]

Roel De Nijs wrote:

Rj Ewing wrote:the getLazilyLoadedData() call

And I assume the lazy loaded data was not yet loaded in the entity you have added on the session. Based on this article, that seems to be the expected behavior of the merge() method. A merge() consists of:

retrieve the entity with the same ID as the detached one passed as argument,

copy the state of the detached entity to the attached one,

and return the attached entity.

So you'll probably need to do update your entity model and cascade merging using the cascade attribute of the relationship annotation e.g. @OneToOne). Something like

@Entity
class Project {
    @OneToOne(cascade=CascadeType.MERGE)
    private Manager manager;
}

More info provided in this article.

Thanks for this. Although it didn't solve my issue, I was able to figure out the problem. When you call manager.merge(myEntity), it returns a new entity. I didn't realize this and was calling the old entity. Anyways I've got it working now. Thanks for the help.

[Roel De Nijs]

Rj Ewing wrote:When you call manager.merge(myEntity), it returns a new entity. I didn't realize this and was calling the old entity. Anyways I've got it working now.

Glad to hear you were able to fix your issue and it's working now!