How to map lazy initialized object in Castor library?

Question

In my Spring MVC application error occurs when castor try to map object which was lazy initilized.

I have Entity class with relation one to many:

@Entity
@Table(name = "a")
public class A implements Serializable {

    ...
    private Set<B> b_set=new HashSet<B>();

    @OneToMany(mappedBy = "a", cascade = CascadeType.ALL, orphanRemoval = true, fetch=FetchType.LAZY)
        public Set<b> getB_set() {
            return b_set;
        }
}

Entity with relation many to one

@Entity
@Table(name = "b")
public class B implements Serializable {
    ...
    @ManyToOne
    @JoinColumn(name = "fk", insertable=false, updatable=false)
    private A a;
}

I use Castor library to map objects to xml.

<mapping>
    <class name="package.a">

        ...
        <field name="b_set" type="package.b" collection="set">
            <bind-xml name="b_name" node="element"></bind-xml>
        </field>

    </class>

    <class name="package.b">
        ...
    </class>
</mapping>

Entity A has a lot of entities B so I have 2 options. Controller can return entity A with lazy init and can also return A with set of B.

@RequestMapping(value = "/name/{name}", method = RequestMethod.GET)
    @ResponseBody
    public A findAByName(@PathVariable String name) {
        return aService.findByName(name);
    }

    @RequestMapping(value = "/b/{name}", method = RequestMethod.GET)
    @ResponseBody
    public A findAByNameWithB(
            @PathVariable String name) {
        return aService.findByNameWithB(name);
    }

In both methods Castor maps returned object and try to map field b_set. In first method there is lazy initialization. Problem occurs when I use first method because castor can not map field b_set:

org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: package.A.b_set, no session or session was closed

I understand this error but I have no idea how to resolve this situation in smart way. I want to have both methods.

I use Spring 3.1.0 Release, castor 1.3.2 and hibernate-entitymanager 3.6.8 Final

I will be grateful for help.

Answer 1

It happens because your hibenrate session is closed before your HTTP response finished.

To solve it you can do the following:

1) Mark collection as EAGER. 2) use Open Session In View pattern.

You can read more about it here:

https://community.jboss.org/wiki/OpenSessionInView

Spring come with out of the box Open Session In View solution. Which is very easy to use:

http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/orm/hibernate3/support/OpenSessionInViewInterceptor.html