How do I save two equal objects in an NHibernate session?

Question

I have the following object structure (simplified):

MainObject
  Person PersonA
  Person PersonB
Person
  string Name
  Status Status

Basically, my MainObject could hold two Person objects. The Person objects will (for this business case) always be different objects, but the Status object on each Person may refer to the same Status (they may both be in status DocumentsUploaded, for example).

Since I am using Fluent NHibernate I get the following exception when I try to save a MainObject when both Persons have the same Status: a different object with the same identifier value was already associated with the session. This makes sense since both Status objects are the same.

When I have googled the error I have mostly found posts where it turns out someone got the same identifier in their session by mistake (and I want to do it on purpose).

I also considered changing the Status field on Person to an integer, but that feels wrong (un-object oriented, if you will).

The question: Is there any way around this, any way to tell NHibernate that, yes, I know that they have the same identifier, but that I would like to save it anyway? If not, what is the reason this is not possible and what is your suggestion?

In case it matters;

Here is the code in my repository:

public void Save<T>(T entity) where T : DomainEntity
{
    using (var session = _sessionSource.CreateSession())
    {
        using (var transaction = session.BeginTransaction())
        {
            session.SaveOrUpdate(entity);
            transaction.Commit();
        }
    }
}

(MainObject, Person and Status all inherit DomainEntity and everything works fine except for the scenario described above)

Edit: Code for loading

This is the simplified code for loading the Status on each of the Persons on the MainObject:

_mainObject.PersonA.Status = _repository.GetStatus(StatusCode.NotSet);
_mainObject.PersonB.Statys = _repository.GetStatus(StatusCode.NotSet);

This is the simplied code for GetStatus in the repository:

public Status GetStatus(StatusCode statusCode)
{
    return Repository.Query<Status>(x => x.StatusCode == statusCode).FirstOrDefault();
}

And this is the code for Query:

public List<T> Query<T>(Expression<Func<T, bool>> expression) where T : DomainEntity
{
    using (var session = _sessionSource.CreateSession())
    {
        using (var transaction = session.BeginTransaction())
        {
            var result = session.Query<T>().Where(expression);
            transaction.Commit();
            return result.ToList();
        }
    }
}

Thanks in advance!

I don't think anything is wrong in principle with what you are trying to achieve. We have some similar code that works just fine. How are you creating/accessing/linking the status object in your code? — fluent
– fluent, Commented Oct 25, 2012 at 14:22
@Chris : Status is a class (which again holds an enum, the text to show etc). — Halvard
– Halvard, Commented Oct 25, 2012 at 14:26
Got it. Is the text a constant value that could be moved into a printer class, allowing Status to become an enum & avoid this problem altogether? — Chris
– Chris, Commented Oct 25, 2012 at 14:34
Is the problem not the micro managing of sessions? I am assuming you have the same style of session code in your load methods. Are you loading the same status object from two different sessions and then trying to reattach the same thing twice to another session when you save. Have you tried wrapping all of this in one session? Is this a web or forms project? — fluent
– fluent, Commented Oct 26, 2012 at 9:52

fluent · Accepted Answer · 2012-10-26 11:33:32Z

2

I believe the problem is the micro management of sessions. If you had one session that covered all of the database transactions I do not believe you would get the issue.

If the project is web service I would suggest that you look at tying the session creation/disposal to the http request.

answered Oct 26, 2012 at 11:33

fluent

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1 Comment

Halvard Over a year ago

Additional remarks: Loading and mixing so many sessions caused the problem. Doing it all in a unit of work (transaction) with one session removed the exception. I will also heed your advice on tying the session life cycle to the http request.

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