Question

I was coding a very simple case with 2 classes: Parent and Child. Parent has n children, and children has 1 Parent. I set up a bidirectional relationship between them.

I was trying to add a business rule to my parent, that rule checked for equality between the child’s parent and the instance handling the call. It returned false when it should have returned true. So I simplified everything to get to the root of the problem. So I tested the same equality outside the POCO and it returned true:

Parent parent0 = session.Load<Parent>(0);
Child child = session.Load<Child>(0);

bool externalTest = parent0 == child.Parent;

I then coded a method for my Parent to test the exact same thing:

bool internalTest = parent0.IsRelated(child);

... Parent Class code

public virtual bool IsRelated(Child child)
{
    return child.Parent == this;            
}
...

And it returns false… I just don’t get it. It’s the exact same code.

More info:

So to get more info, I modified my test:

Parent parent0 = session.Load<Parent>(0);
Child child = session.Load<Child>(0);

bool externalTest = parent0 == child.Parent;
System.Diagnostics.Debug.WriteLine("outside parent: " + externalTest);
System.Diagnostics.Debug.WriteLine("Number of parent instances before call to IsRelated:" + Parent.NumberOfInstances);
parent0.IsRelated(child, parent0);
System.Diagnostics.Debug.WriteLine("Number of parent instances after call to IsRelated:" + Parent.NumberOfInstances);

... Parent Class code
public virtual void IsRelated(Child child, Parent sameAsThis)
{
    bool internalTest = child.Parent == this;
    System.Diagnostics.Debug.WriteLine("inside parent:" + internalTest);

    bool sameTest = sameAsThis == this;
    System.Diagnostics.Debug.WriteLine("this should equal sameAsThis:" + sameTest);

}
...

I passed the parent instance directly to itself and verify it was the same instance. Well it’s not, I get another instance created when I enter the IsRelatedMethod.

Here are my test results:

outside parent: True

Number of parent instances before call to IsRelated:1

inside parent:False

this should equal sameAsThis:False

Number of parent instances after call to IsRelated:2

What am I doing wrong ?

For detailed mapping files and pocos, see (http://stackoverflow.com/questions/13253459/relationships-fixup-in-entityframework-vs-nhibernate)

Answer 1

This is because of the proxy that Nhibernate uses to lazy load entities. In your case the child’s parent is a proxy instance.

To solve you problem simply change .Load to .Get

.load does not actually hit the database and populate the entity. See this blog post by Ayende for more info