编码第一个一对多关系

Question

I have defined one to many relationship like this

    public class ClassA
    {
        [Key, ForeignKey("ClassB"), Column(Order = 0)]
        public int ClassB_ID { get; set; }
         [Key, Column(Order=1)]
        public string  name { get; set; }
        public bool IsApproved { get; set; }
        public virtual ClassB ClassB { get; set; }
     }
    public class ClassB
    {
     [Key]
     public int ID{get;set;}
     public string Name{get;set;}
     public virtual ICollection<ClassA> classAs{get;set;}
    }

Works fine until I bind classA to a Listview with Bind(ClassB.Name)

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

Answer 1

This could be because of using Lazy Loading . Which cause the additional round trip to database when trying to access with navigation property (ClassA), but your context is already disposed.

Lazy Loading : When the entity is first read, related data isn't retrieved. However, the first time you attempt to access a navigation property, the data required for that navigation property is automatically retrieved. This results in multiple queries sent to the database.

You could probably solve this problem with Eager Loading Include() or Explicit loading .

var values = context.ClassB.Include("ClassA").ToList()

http://www.asp.net/web-forms/tutorials/continuing-with-ef/maximizing-performance-with-the-entity-framework-in-an-asp-net-web-application