Fix IsModified so that a null equates empty components when using select-before-update.

[druidroad]

The equality check used by the ComponentType.IsModified method must treat empty (all properties null) components equivalent to null component properties and vice versa.

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Originally this was about another failure in IsModified, but checking its current state in Hibernate incites to fix this other more troublesome bug. See this comment for all details.

[hazzik]

Seems legit. On Hibernate side they "fixed" it in HHH-11237 (hibernate/hibernate-orm@667136c + hibernate/hibernate-orm@550c2e3)

[druidroad]

Thank you Alexander, for pointing out. I will follow HHH-11237 and update the issue.

[druidroad]

Moving original issue text to the comments, replacing it with Hibernate HHH-11237

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Old title: #1486 ComponentType.IsModified(…) method throws exception (Unable to cast...)

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Old description:

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PROBLEM:
We are using EventListener(IPostUpdateEventListener) in our application to audit data changes:

foreach (int index in e.Persister.FindModified(e.OldState, e.State, e.Entity, e.Session))
{
    // Log changes
}

FindModified method calls IsModified method for each individual property of the object. IsModified throws exception on the component type:

Result StackTrace:

at NHibernate.Type.ComponentType.IsModified(Object old, Object current, Boolean[] checkable, ISessionImplementor session) in nhibernate-core-test\src\NHibernate\Type\ComponentType.cs:line 537

Result Message:

System.InvalidCastException : Unable to cast object of type ‘MyType' to type 'System.Object[]'.

CAUSE:
NHibernate throws exception in method:

ComponentType.IsModified(object old, object current, bool[] checkable, ISessionImplementor session)

On the line:

object[] oldValues = (Object[]) old;

Basically, Nhibernate is trying to cast ComponentType to object[].

SOLUTION:
Changing line:

object[] oldValues = (Object[]) old;

TO:

object[] oldValues = GetPropertyValues(old, session);

OR

object[] oldValues = old is object[] ? (Object[])old : GetPropertyValues(old, session);

fixes the problem.
The method IsDirty(…) is done that way: it uses GetPropertyValues for “old” and “current” object.

[hazzik]

@mishaurubkov have you closed this by accident?

[druidroad]

Sorry. Closed by accident.