@Reference(lazy = true) fails on database read with circular references

[darbie]

When I have 2 classes, say class A and class B that both have a reference to each other using @reference, things work fine. However if I use "@reference(lazy = true) the code throws an exception on the read of one of the objects.

I am using these dependencies in my gradle project:
compile 'org.mongodb.morphia:morphia:0.1+'
compile 'cglib:cglib:2.+'
compile 'com.thoughtworks.proxytoys:proxytoys:1.+'

Here is sample code that shows the bug (the exception it produces is after the code):

import java.util.Iterator;
import java.util.UUID;

import org.mongodb.morphia.Datastore;
import org.mongodb.morphia.Morphia;
import org.mongodb.morphia.annotations.Entity;
import org.mongodb.morphia.annotations.Id;
import org.mongodb.morphia.annotations.Reference;

import com.mongodb.MongoClient;

public class Main
{

  public static void main(String[] args) throws Exception
  {
    Main main = new Main();
    main.go();
  }

  private void go() throws Exception
  {
    A a = new A(UUID.randomUUID().toString());
    B b = new B(UUID.randomUUID().toString());

    a.setB(b);
    b.setA(a);

    MongoClient mongoClient = new MongoClient();
    Morphia morphia = new Morphia();
    morphia.map(A.class, B.class);

    Datastore datastore = morphia.createDatastore(mongoClient, "dbName");
    datastore.save(a);
    datastore.save(b);

    Iterator it = datastore.createQuery(A.class).iterator();
    while (it.hasNext())
    {
      A newA = it.next();
      B newB = newA.getB();
      System.out.println(newA);
      System.out.println(newB);
    }
  }
}

@Entity(value = "collectionA", noClassnameStored = true)
class A
{
  @Id
  private String id;
  @Reference(lazy = true)
  private B b;

  private A()
  {
  }

  A(String id)
  {
    this.id = id;
  }

  void setB(B b)
  {
    this.b = b;
  }

  B getB()
  {
    return b;
  }
}

@Entity(value = "collectionB", noClassnameStored = true)
class B
{
  @Id
  private String id;
  @Reference(lazy = true)
  private A a;

  private B()
  {
  }

  B(String id)
  {
    this.id = id;
  }

  void setA(A a)
  {
    this.a = a;
  }

  A getA()
  {
    return a;
  }
}

Here is the stack trace I get:

Apr 22, 2014 1:36:43 PM org.mongodb.morphia.logging.MorphiaLoggerFactory chooseLoggerFactory
INFO: LoggerImplFactory set to org.mongodb.morphia.logging.jdk.JDKLoggerFactory
Exception in thread "main" net.sf.cglib.core.CodeGenerationException: java.lang.NoSuchMethodException-->B$$EnhancerByCGLIB$$db68ebca.()
    at net.sf.cglib.core.ReflectUtils.getConstructor(ReflectUtils.java:248)
    at net.sf.cglib.core.ReflectUtils.newInstance(ReflectUtils.java:220)
    at net.sf.cglib.proxy.Enhancer.createUsingReflection(Enhancer.java:639)
    at net.sf.cglib.proxy.Enhancer.firstInstance(Enhancer.java:538)
    at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:225)
    at net.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java:377)
    at net.sf.cglib.proxy.Enhancer.create(Enhancer.java:304)
    at com.thoughtworks.proxy.factory.CglibProxyFactory.createWithConstructor(CglibProxyFactory.java:150)
    at com.thoughtworks.proxy.factory.CglibProxyFactory.createProxy(CglibProxyFactory.java:105)
    at com.thoughtworks.proxy.toys.hotswap.HotSwappingInvoker.proxy(HotSwappingInvoker.java:153)
    at org.mongodb.morphia.mapping.lazy.CGLibLazyProxyFactory.createProxy(CGLibLazyProxyFactory.java:33)
    at org.mongodb.morphia.mapping.ReferenceMapper.createOrReuseProxy(ReferenceMapper.java:379)
    at org.mongodb.morphia.mapping.ReferenceMapper.readSingle(ReferenceMapper.java:189)
    at org.mongodb.morphia.mapping.ReferenceMapper.fromDBObject(ReferenceMapper.java:176)
    at org.mongodb.morphia.mapping.Mapper.readMappedField(Mapper.java:608)
    at org.mongodb.morphia.mapping.Mapper.fromDb(Mapper.java:585)
    at org.mongodb.morphia.mapping.Mapper.fromDBObject(Mapper.java:296)
    at org.mongodb.morphia.query.MorphiaIterator.convertItem(MorphiaIterator.java:78)
    at org.mongodb.morphia.query.MorphiaIterator.processItem(MorphiaIterator.java:65)
    at org.mongodb.morphia.query.MorphiaIterator.next(MorphiaIterator.java:60)
    at Main.go(Main.java:41)
    at Main.main(Main.java:19)
Caused by: java.lang.NoSuchMethodException: B$$EnhancerByCGLIB$$db68ebca.()
    at java.lang.Class.getConstructor0(Class.java:2810)
    at java.lang.Class.getDeclaredConstructor(Class.java:2053)
    at net.sf.cglib.core.ReflectUtils.getConstructor(ReflectUtils.java:244)
    ... 21 more

[evanchooly]

We're a little leery of the circular reference and so there's some debate about if morphia should support such a case. On the other hand, normal loads do have a cache to track already seen entities and so it would seem that it's just not being used for lazy loads. Bumping to post-1.0 for now unless there's strong sentiment otherwise.