NHibernate - LAZY LOADING PROBLEM -Initializing [] - 无法初始化代理 - 没有会话."}

Question

嗨我使用Fluent NHibernate,我对Lazy Loading感到困惑.

1. 我查询了数据库中的对象
2. 修改的对象属性
3. 使用此对象更新数据库

这是代码:

public class Credentials
{
    public virtual int Id { get; set; }
    public virtual string Nick { get; set; }
    public virtual string Password { get; set; }
}

public class CredentialsMap : ClassMap<Credentials>
{
    public CredentialsMap()
    {
        Id(x => x.Id);
        Map(x => x.Nick).Column("NICK");
        Map(x => x.Password).Column("PASSWORD");
        Table("R_CREDENTAILS");
    }
}

public class Status
{
    public virtual int Id { get; set; }
    public virtual string Msg { get; set; }
    public virtual DateTime AddTime { get; set; }
}

public class StatusMap : ClassMap<Status>
{
    public StatusMap()
    {
        Id(x => x.Id);
        Map(x => x.Msg).Column("MESSAGE");
        Map(x => x.AddTime).Column("ADD_TIME");
        Table("R_STATUS");
    }
}

public class Account
{
    public virtual int Id { get; set; }
    public virtual string SelfNick { get; set; }
    public virtual Credentials Credentials { get; set; }
    public virtual Status Status { get; set; }
}

public class AccountMap : ClassMap<Account>
{
    public AccountMap()
    {
        Id(x => x.Id);
        Map(x => x.SelfNick).Column("SELF_NICK");
        References(x => x.Credentials)
            .Column("CREDENTIALS_ID")
            .ForeignKey();
        References(x => x.Status)
            .Column("STATUS_ID")
            .ForeignKey();
        Table("R_ACCOUNTS");
    }
}

NHibernate配置类:

public class NHiberanteHelper
{
    private static ISessionFactory _sessionFactory;

    private static ISessionFactory SessionFactory
    {
        get
        {
            if (_sessionFactory == null)
                InitializeSessionFactory();

            return _sessionFactory;
        }
    }

    private static void InitializeSessionFactory()
    {
        _sessionFactory = Fluently.Configure()
            .Database(MsSqlConfiguration.MsSql2008
                          .ConnectionString(
                               @"Server=TEST\SQLEXPRESS;Database=SimpleNHibernate;Trusted_Connection=True;").
                               ShowSql()
                              )
            .Mappings(m => m.FluentMappings.AddFromAssemblyOf<Account>().Conventions.Add( DefaultCascade.All()))
            .ExposeConfiguration(cfg => new SchemaUpdate(cfg).Execute(true, true))
            .BuildSessionFactory();
    }

    public static ISession OpenSession()
    {
        return SessionFactory.OpenSession();
    }
}

这是用法:

    public class LoginDbHelper
    {
        public static Account GetAccount(string nick)
        {
            using (var session = NHiberanteHelper.OpenSession())
            {
                var account = (session.QueryOver<Account>()
                    .JoinQueryOver<Credentials>(a => a.Credentials)
                    .Where(c => c.Nick == nick));

                if (account != null)
                    return account.SingleOrDefault();

                return null;
            }
        }

        public static void SaveOrUpdateAccount(Account account)
        {
            using (var session = NHiberanteHelper.OpenSession())
            {
                using (var trans = session.BeginTransaction())
                {
                    session.SaveOrUpdate(account);
                    trans.Commit();
                }
            }
        }
   }

问题代码:

var actualAccount = LoginDbHelper.GetAccount(nick);

//modify
actualAccount.Status.Msg = "New status 2";
actualAccount.Status.AddTime = DateTime.Now;


LoginDbHelper.SaveOrUpdateAccount(account);

我收到此错误:

{"Initializing[NHibernateSample1.Status#1]-Could not initialize proxy - no Session."}

堆栈跟踪:

 at NHibernate.Proxy.AbstractLazyInitializer.Initialize() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Proxy\AbstractLazyInitializer.cs:line 113
   at NHibernate.Proxy.AbstractLazyInitializer.GetImplementation() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Proxy\AbstractLazyInitializer.cs:line 191
   at NHibernate.ByteCode.Castle.LazyInitializer.Intercept(IInvocation invocation) in d:\CSharp\NH\NH\nhibernate\src\NHibernate.ByteCode.Castle\LazyInitializer.cs:line 61
   at Castle.DynamicProxy.AbstractInvocation.Proceed()
   at Castle.Proxies.StatusProxy.set_Msg(String value)
   at NHibernateSample1.Program.Main(String[] args) in E:\C# PROJECTS\Samples\SimpleNHibernateClient\NHibernateSample1\Program.cs:line 215
   at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
   at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
   at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()

我谷歌它,我认为它是由懒惰加载导致因为在方法GetAccount我关闭SESSION.这是我对NHibernate的第一次尝试,所以如何才能正确解决这个问题？如果是的话可以禁用LAZY LOADING怎么做？

Answer 1

你是对的.因为NHibernate会话在GetAccount方法中关闭(它只在using语句的范围内打开),所以不能在此方法之外加载其他对象.有2个可能的修复:

1. 在操作级别(即在包含问题代码的方法中)创建会话,然后在get&save方法中使用此会话.您可以通过将其作为参数传递给方法来使用会话.
2. 将对象更改为不使用延迟加载.您可以通过添加.Not.LazyLoad()到StatusFluent映射中的对象来完成此操作.

Answer 2

我发现关闭延迟加载的最简单方法是添加 DefaultLazy 约定，即：

.Conventions.Add( DefaultCascade.All(), DefaultLazy.Never() )

请注意，打开延迟加载 (DefaultLazy.Always()) 确实可以提高性能，具体取决于您的应用程序。

缺点是，您始终必须打开一个会话，然后才能延迟加载实体中的其余数据。根据我的经验，支持延迟加载的会话管理是 NHibernate 的一大痛点。