NHibernate lazy loading and object comparison

Question

With lazy loading configured, I run into an issue regarding object comparison. My overriden Equals-method within each domain entity class contains the following line:

if (obj == null || !obj.GetType().Equals(GetType()))

Obviously, The type comparison will fail as obj is a proxy instance. I've already seen some NHibernate-snippets which unproxy an object and return the real instance. But as I enforce a domain driven design, I do not want any ORM-specific code within my domain layer. I also cannot unproxy the instance on caller side [e.g. foo.Equals(Unproxy(bar))] as the caller is my application layer which also doesn't contain any ORM-specific code (all NHibernate dependencies are injected by Windsor).

Long story short: is there any generic code to get the real instance?

Why do you want to get the type for the equality comparison? Doesn't your entity have a natural identity to compare on? If it's a value object you'd compare on the attributes... — MattDavey
Well but if I only compare the natural id and I got domain object types A, B and instances A a, B b and a.id = b.id, my Equals-method would return true, even if the objects are totally different. E.g. a car and a dog both with id = 1 would be considered as true. — mbue
ah, I thought you were talking about IEquatable.Equals - my mistake! — MattDavey

Trevor Pilley Trevor Pilley · Accepted Answer · 2012-10-16T11:24:52

The way to solve that is to do a cast:

public class Person
{
    public int Id { get; set; }

    public override bool Equals(object obj)
    {
        var person = obj as Person;

        if (person == null)
        {
            return false;
        }

        return person.Id == this.Id;
    }
}

The cast works because the proxy inherits from your class (e.g. PersonProxy : Person)

The null check is unnecessary as the as cast will just return null if obj is either null or not an object that can be cast as a person.

NHibernate lazy loading and object comparison

2 Answers