是时候再次吸引更伟大的思想了。

我正在经历一个非常奇怪的现象。正如标题所述，我在尝试创建 EF ObjectContext 时收到 NullReferenceException，但只有在 Using 语句中创建上下文时才会收到异常。我尝试了各种不同的方法，但结果总是一样。而且，当然，这是直到昨天都运行良好的代码。我的 Windows 更新昨天早上运行可能与此相关。

反正...

如果我试试这个

using (var context = new Entities(Env.Instance.Connection))
{
    //do a bunch of EF stuff
}

var context = new Entities(Env.Instance.Connection);
//do a bunch of EF stuff
context.Dispose();

using (var context = new Entities(Env.Instance.ConnectionName)) //the name of a connection string in my App.Config
{
    //do a bunch of EF stuff
}

using (var context = new Entities(Env.Instance.ConnectionString)) //the actual connection string
{
    //do a bunch of EF stuff
}

using (var context = new Entities("metadata=res://*/MyDB.csdl|res://*/MyDB.ssdl|res://*/MyDB.msl;provider=System.Data.SqlClient;provider connection string=\"data source=MY-DB;initial catalog=MY-DB-PROD;persist security info=True;user id=dbuser;password=dbpass;multipleactiveresultsets=True;App=EntityFramework\""))
{
    //do a bunch of EF stuff
}

public Entities(string connectionString) : base(connectionString, "Entities")
{
    this.ContextOptions.LazyLoadingEnabled = true;
    OnContextCreated();
}

at IkaPlus.ViewModel.MainVM.ProcessMail3(Object sender, DoWorkEventArgs e) in C:\SVN\IkaPlus\IkaPlus\ViewModel\MainVM.cs:Line 1371.
at IkaPlus.ViewModel.MainVM.RefillQueues() in C:\SVN\IkaPlus\IkaPlus\ViewModel\MainVM.cs:Line 832.

private void RefillQueues()
{
    using (var context = new Entities("metadata=res://*/MyDB.csdl|res://*/MyDB.ssdl|res://*/MyDB.msl;provider=System.Data.SqlClient;provider connection string=\"data source=MY-DB;initial catalog=MY-DB-PROD;persist security info=True;user id=dbuser;password=dbpass;multipleactiveresultsets=True;App=EntityFramework\""))
    {
    }

    ProcessMail3(null, null);
}

private void ProcessMail3(object sender, DoWorkEventArgs e)
{
    using (var context = new Entities("metadata=res://*/MyDB.csdl|res://*/MyDB.ssdl|res://*/MyDB.msl;provider=System.Data.SqlClient;provider connection string=\"data source=MY-DB;initial catalog=MY-DB-PROD;persist security info=True;user id=dbuser;password=dbpass;multipleactiveresultsets=True;App=EntityFramework\""))
    {
    }
}

private void RefillQueues()
{
    using (var context = new Entities("metadata=res://*/MyDB.csdl|res://*/MyDB.ssdl|res://*/MyDB.msl;provider=System.Data.SqlClient;provider connection string=\"data source=MY-DB;initial catalog=MY-DB-PROD;persist security info=True;user id=dbuser;password=dbpass;multipleactiveresultsets=True;App=EntityFramework\""))
    {
    }

    ProcessMail3();
}

private void ProcessMail3()
{
    using (var context = new Entities("metadata=res://*/MyDB.csdl|res://*/MyDB.ssdl|res://*/MyDB.msl;provider=System.Data.SqlClient;provider connection string=\"data source=MY-DB;initial catalog=MY-DB-PROD;persist security info=True;user id=dbuser;password=dbpass;multipleactiveresultsets=True;App=EntityFramework\""))
    {
    }
}

private void EatCookies()
{
    #region Empty the Queue

    string s = "Queue 3";

    CicConnector.CreateInstance(SettingsHandler.Instance.CIC_PASSWORD,
              "MYSERVER",
              "C:\\temp");

    //Do a bunch of stuff

    #endregion

    #region EF Stuff

    using (var context = new Entities("metadata=res://*/MyDB.csdl|res://*/MyDB.ssdl|res://*/MyDB.msl;provider=System.Data.SqlClient;provider connection string=\"data source=MY-DB;initial catalog=MY-DB-PROD;persist security info=True;user id=dbuser;password=dbpass;multipleactiveresultsets=True;App=EntityFramework\""))
    {
    }

    #endregion
}

private void RefillQueues()
{
    string s = "Queue 3";

    CicConnector.CreateInstance(SettingsHandler.Instance.CIC_PASSWORD,
              "MYSERVER",
              "C:\\temp");

    using (var context = new Entities("metadata=res://*/MyDB.csdl|res://*/MyDB.ssdl|res://*/MyDB.msl;provider=System.Data.SqlClient;provider connection string=\"data source=MY-DB;initial catalog=MY-DB-PROD;persist security info=True;user id=dbuser;password=dbpass;multipleactiveresultsets=True;App=EntityFramework\""))
    {
    }

    EatCookies();
}

private void EatCookies()
{
    string s = "Queue 3";

    CicConnector.CreateInstance(SettingsHandler.Instance.CIC_PASSWORD,
              "MYSERVER",
              "C:\\temp");

    using (var context = new Entities("metadata=res://*/MyDB.csdl|res://*/MyDB.ssdl|res://*/MyDB.msl;provider=System.Data.SqlClient;provider connection string=\"data source=MY-DB;initial catalog=MY-DB-PROD;persist security info=True;user id=dbuser;password=dbpass;multipleactiveresultsets=True;App=EntityFramework\""))
    {
    }
}

最佳答案

EF 为您管理处置，因此自己使用或明确处置它有点多余 http://blog.jongallant.com/2012/10/do-i-have-to-call-dispose-on-dbcontext.html
文章摘录

Before I talked with the devs on the EF team my answer was always a resounding “of course!”. But it’s not true with DbContext. You don’t need to be religious about calling Dispose on your DbContext objects. Even though it does implement IDisposable, it only implements it so you can call Dispose as a safeguard in some special cases. By default DbContext automatically manages the connection for you. Read to the end to hear the full story and see what the EF devs had to say about it.

关于c# - 在 Using 语句中创建 ObjectContext 时出现 NullReferenceException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33667931/