Nhibernate one-to-many lazy loading not working as expected

Question

Consider the following scenario:

Class A has a one-to-many relationship to Class B. Class B has a many-to-one relationship to Class C.

class A {
  IList<B> BList {get;set;}
}
class B {
  C CMember{get;set;}
}

class C {
   //null
}

If I load class B from the database using something like

   IList<B> result = query.List<B>();

everything works as expected,

However if I do something like:

   DetachedCriteria query = DetachedCriteria.For(typeof(A));
   query.CreateAlias("B", "B", JoinType.InnerJoin);
   IList<A> result = query.List<A>();

then, NHibernate will also select from table C and load all Cs.

Mappings below: A mapping...

<bag name="BList " table="B" lazy="true" inverse="false">
    <key column="id" />
    <one-to-many class="B" />
    </bag>

B mapping...

<many-to-one class="C" name="CMember" column="idC" lazy="proxy" outer-join="true" />

Any Ideas? Thanks.

You got your hibernate session still open when you're trying to access the lazy-loaded collections? — Chris
– Chris, Commented Jul 20, 2010 at 0:53

rabs · Accepted Answer · 2011-06-15 06:53:09Z

1

I have created a sample app to test the scenario you outline and I was not able to reproduce a difference between the Criteria and the DetachedCriteria, they both returned the same result for me.

Whether or not the load obeys the lazy property was dependant on the outer-join attribute, when it is set I always got C loaded eagerly, when I removed the outer-join attribute it lazy loaded C through a proxy.

So one possible solution is to change the B mapping to:

<many-to-one class="C" name="CMember" column="idC" lazy="proxy"/>

answered Jun 15, 2011 at 6:53

rabs

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