Note: See my own answer to this question for an example of how I solved this issue.
I am getting the following exception in my Spring MVC 4 + Hibernate 4 project:
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.mysite.Company.acknowledgements, could not initialize proxy - no Session
After reading a lot of other questions about this issue, I understand why this exception occurs, but I am not sure how to fix it in a good way. I am doing the following:
- My Spring MVC controller calls a method in a service
- The service method invokes a method in a DAO class
- The method in the DAO class fetches an entity object through Hibernate and returns it to the calling service
- The service returns the fetched object to the controller
- The controller passes the object to the view (JSP)
- The view tries to iterate on a many-to-many association that is lazily loaded (and is thus a proxy object)
- The exception is thrown because the session is closed at this point, and the proxy cannot load the associated data
I have previously worked with PHP and doctrine2, and this way of doing things caused no problems. I am trying to figure out the best way to solve this, because the solutions that I found so far don't seem so great:
- Load the association eagerly, potentially loading lots of unnecessary data
- Call
Hibernate.initialize(myObject.getAssociation());- this means that I have to loop through associations to initialize them (I guess), and just the fact that I have to do this, kind of makes the lazy loading less neat - Using a Spring filter to leave the session open in the views, but I doubt that this is a good thing to do?
I tried to use @Transactional in my service, but without 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 within my view. I guess the drawback of initializing the associations within my service is that I have to explicitly define which data I need - but this depends on the context (controller) in which the service is used. I am not sure if I can do this within my controller instead without losing the abstraction that the DBAL layer provides. I hope that makes sense. Either way, it would be great if I didn't have to always explicitly define which data I want to be available to my view, but just let the view do its thing. If that is not possible, then I am 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
@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
}
Acknowledgement entity
@Entity
public class Acknowledgement {
@Id
private int id;
// Other fields + getters and setters here
}
mvc-dispatcher-servlet.xml (a 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!
