Spring MVC + Hibernate: unable to initialize proxy - no session

Note: See my own answer to this question for an example of how I solved this problem.

I am getting the following exception in my Spring MVC 4 + Hibernate 4 project:

org.hibernate.LazyInitializationException: Failed to lazily initialize the role collection: com.mysite.Company.Updates, Failed to initialize proxy - no session

After reading many other questions on this issue, I understand why this exception is happening, but I'm not sure how to fix it. I am doing the following:

• My Spring MVC Controller calls a method on a service
• Service method calls method in DAO class
• DAO class method retrieves the object object via Hibernate and returns it to the calling service
• The service returns the selected object to the controller
• Controller passes object to view (JSP)
• The view tries to iterate over a many-to-many association that is lazy loaded (and therefore a proxy).
• The exception is thrown because the session is closed at this point and the proxy is unable to load associated data

I've worked with PHP and doctrine2 previously and this way of doing things didn't cause any problems. I'm trying to find the best way to solve this problem, because the solutions I've found so far don't seem so great:

• Load the association anxiously, potentially loading a lot of unnecessary data.
• Call Hibernate.initialize(myObject.getAssociation());
  
  - This means I have to iterate over associations to initialize them (I think), and just the fact that I have to do this kind of makes lazy loading less tidy
• Using a Spring filter to keep the session open in views, but I doubt it's a good idea to do this?

I tried to use @Transactional

in his service, but no luck. This makes sense because I am trying to access data that has not yet been loaded after my service method returns. Ideally I would like to be able to access any association from my view. I guess the downside to initializing associations in my service is that I have to explicitly define what data I need, but that depends on the context (controller) in which the service is being used. I'm not sure if I can do this in my controller without losing the abstraction that the DBAL layer provides. I hope this makes sense. Anyway, it would be great if I didn't have to always explicitly define what data I want to be available for my view, but just let that view do something. If this is not possible,I'm just looking for the most elegant solution to the problem.

Below is my code.

View

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<h1><c:out value="${company.name}" /> (ID: <c:out value="${company.id}" />)</h1>

<c:forEach var="acknowledgement" items="${company.acknowledgements}">
    <p><c:out value="${acknowledgement.name}" /></p>
</c:forEach>

      

        
        
        
      

    

controller

@Controller
public class ProfileController {
    @Autowired
    private CompanyService companyService;

    @RequestMapping("/profile/view/{id}")
    public String view(Model model, @PathVariable int id) {
        Company company = this.companyService.get(id);
        model.addAttribute("company", company);

        return "viewCompanyProfile";
    }
}

      

        
        
        
      

    

Service

@Service
public class CompanyServiceImpl implements CompanyService {
    @Autowired
    private CompanyDao companyDao;

    @Override
    public Company get(int id) {
        return this.companyDao.get(id);
    }
}

      

        
        
        
      

    

DAO

@Repository
@Transactional
public class CompanyDaoImpl implements CompanyDao {
    @Autowired
    private SessionFactory sessionFactory;

    @Override
    public Company get(int id) {
        return (Company) this.sessionFactory.getCurrentSession().get(Company.class, id);
    }
}

      

        
        
        
      

    

Company

@Entity
@Table(name = "company")
public class Company {
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private int id;

    // Other fields here

    @ManyToMany
    @JoinTable(name = "company_acknowledgement", joinColumns = @JoinColumn(name = "company_id"), inverseJoinColumns = @JoinColumn(name = "acknowledgement_id"))
    private Set<Acknowledgement> acknowledgements;

    public Set<Acknowledgement> getAcknowledgements() {
        return acknowledgements;
    }

    public void setAcknowledgements(Set<Acknowledgement> acknowledgements) {
        this.acknowledgements = acknowledgements;
    }

    // Other getters and setters here
}

      

        
        
        
      

    

Confirmation object

@Entity
public class Acknowledgement {
    @Id
    private int id;

    // Other fields + getters and setters here

}

      

        
        
        
      

    

mvc-dispatcher-servlet.xml (part of it)

<bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="packagesToScan">
            <list>
                <value>com.mysite.company.entity</value>
            </list>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">org.hibernate.dialect.PostgreSQL9Dialect</prop>
            </props>
        </property>
    </bean>

    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource" />
    </bean>

    <tx:annotation-driven />

      

        
        
        
      

    

Thanks in advance!