NHibernate维护Isession对象的方法

Question

My code is as below. My problem is when I use NHibernate to retrieve an object that contains a navigation property and try to set a value in that navigation property object it throws an error saying that session does not exist.

[The 'f.HIERARCHY.CHANGETIME = DateTime.Now;' line inside the main method]

I understand that this is because when NHibernate tries to fetch the 'HIERARCHY' object the session is already closed inside the repository class

What I need to know is the standard approach to write the code so that I can still use lazy loading but can access the properties of navigation objects later in the code WITHOUT disabling lazy loading.

Is it a good approach to always keep the Isession object open? Most of the code samples i found on internet always opens up a new session at each CRUD operation for each operation and closes it immediately after. How do they address the issue of accessing navigation properties later in the code?

 public class NHibernateBaseRepository : IDisposable { private ISessionFactory m_SessionFactory = null; private ISession m_Session = null; public T GetById<T>(long id) { using (ISession session = m_SessionFactory.OpenSession()) { return session.Get<T>(id); } } } public class ROLE { public virtual string RoleComment { get; set; } public virtual HIERARCHY HIERARCHY { get; set; } } public class HIERARCHY_STRUCTURE { public virtual DateTime CHANGETIME{ get; set; } } class Program { static void Main(string[] args) { NHibernateBaseRepository persistenceManager = new NHibernateBaseRepository(); ROLE f = persistenceManager.GetById<ROLE>(34); f.RoleComment = "Test Com"; f.HIERARCHY.CHANGETIME = DateTime.Now; //Throws error persistenceManager.SaveOrUpdateEntitiy<ROLE>(f); } } 

Answer 1

How do they address the issue of accessing navigation properties later in the code?

WITHOUT disabling lazy loading

Try to use Fetch() method in repository when the session is open. For example:

private IList<Container> ReadContainer()
{
        var modeList = new List<Container>();

        using (var session = DatabaseHelper.OpenSession())
        {
            var tmp = session.Query<Container>().Fetch(items => items.TmcList).ToList();
        }
        return modeList;
    }

Answer 2

Mainly what you need to do is change how you manage the lifetime of your Session object and make it isolated of your single repository method call, this will give you benefits like write and query batching.

That means, that you have to define a Session in a more global manner, maybe as a private field in your NHibernateBaseRepository class, instantiate it in the constructor and then implement IDisposable and in the Dispose method, close your session. this way you can do multiple actions (and a more consistent unit of work) on the same session.

Some code example:

NHibernateBaseRepository class:

public class NHibernateBaseRepository : IDisposable
{
    private ISession _session;

    public NHibernateBaseRepository ()
    {
        _session = m_SessionFactory.OpenSession(); //session factory should be created once per application lifetime, not per instance.
    }

    public void Dispose()
    {
        _session.Dispose();
    }

    public T GetById<T>(long id)
    {
        return _session.Get<T>(id); 
    }
}

Main method:

static void Main(string[] args)
{
     using(var persistenceManager = new NHibernateBaseRepository())
     {
         ROLE f = persistenceManager.GetById<ROLE>(34);

         f.RoleComment = "Test Com";
         f.HIERARCHY.CHANGETIME = DateTime.Now; //Throws error
         persistenceManager.SaveOrUpdateEntitiy<ROLE>(f);
     }
}