c# - 异常类型 'System.ObjectDisposedException'

Question

我有以下 EF 代码优先代码。它工作正常。但是当我查找“club2.Members”的值时，它显示如下:

'club2.Members' threw an exception of type 'System.ObjectDisposedException'.

消息是:

The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

我没有为 Members 属性设置值。没关系。但是，它不应在内部引起任何异常。

1. 有没有办法克服这个异常？
2. 移除此异常是否有助于提高性能？
3. 为什么这个异常没有导致程序执行终止？

注意:我不需要俱乐部实体中的成员(member)数据(在我调用的地方)。甚至当时还没有成员加入俱乐部。我所需要的只是摆脱异常；不要使用 eager load 加载数据。如何避免异常？

namespace LijosEF
{

public class Person
{
    public int PersonId { get; set; }
    public string PersonName { get; set; }
    public virtual ICollection<Club> Clubs { get; set; }
}

public class Club 
{
    public int ClubId { get; set; }
    public string ClubName { get; set; }
    public virtual ICollection<Person> Members { get; set; }

}




//System.Data.Entity.DbContext is from EntityFramework.dll
public class NerdDinners : System.Data.Entity.DbContext
{

    public NerdDinners(string connString): base(connString)
    { 

    }

    protected override void OnModelCreating(DbModelBuilder modelbuilder)
    {
         //Fluent API - Plural Removal
        modelbuilder.Conventions.Remove<PluralizingTableNameConvention>();
    }

    public DbSet<Person> Persons { get; set; }
    public DbSet<Club> Clubs { get; set; }



}
}




    static void Main(string[] args)
    {
        Database.SetInitializer<NerdDinners>(new MyInitializer());

        CreateClubs();
        CreatePersons();

    }

    public static void CreateClubs()
    {

        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            Club club1 = new Club();
            club1.ClubName = "club1";

            Club club2 = new Club();
            club2.ClubName = "club2";

            Club club3 = new Club();
            club3.ClubName = "club3";

            db.Clubs.Add(club1);
            db.Clubs.Add(club2);
            db.Clubs.Add(club3);

            int recordsAffected = db.SaveChanges();


        }
    }

    public static Club GetClubs(string clubName)
    {
        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            var query = db.Clubs.SingleOrDefault(p => p.ClubName == clubName);
            return query;
        }
    }

    public static void CreatePersons()
    {
        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            Club club1 = GetClubs("club1");
            Club club2 = GetClubs("club2");
            Club club3 = GetClubs("club3");

             //More code to be added (using db) to add person to context and save
        }
    }

Answer 1

您收到此错误是因为您在执行查询后处理了 dbcontext。如果您想使用“成员”中的数据，请使用查询加载它: http://blogs.msdn.com/b/adonet/archive/2011/01/31/using-dbcontext-in-ef-feature-ctp5-part-6-loading-related-entities.aspx

如果您不需要延迟加载，这意味着只加载您在查询中加载的数据(这将消除异常)，请设置 LazyLoadingEnabled = false。看这里: Disable lazy loading by default in Entity Framework 4