c# - How to map ICollection<Type> to extending class -

i have created data model looks this:

// base data item class public class dataitem {     [key]     public int id { get; set; }     public string name { get; set; }            [required]     public int dataitemgroupid { get; set; }     public virtual dataitemgroup dataitemgroup { get; set; } }  // extending data item class public class specificdataitem : dataitem {     public string extrafield { get; set; }        }  // class grouping of data items may extended or not. public class dataitemgroup {     [key]     public int id { get; set; }     public string name { get; set; }            public virtual icollection<dataitem> dataitems { get; set; }     public virtual icollection<extendeddataitem> extendeddataitems { get; set; } } 

my issues when use entity frameworks lazy loading, dataitemgroup.dataitems populated items, including extendeddataitems, dataitemgroup.extendeddataitems empty.

i suspect missing mapping of sort, don't know should looking for. ideas on how dataitemgroup load both dataitems , extendeddataitems collections through lazy loading?

you create 1 relationship using base class (dataitem):

public class dataitemgroup {   [key]   public int id { get; set; }   public string name { get; set; }          public virtual icollection<dataitem> dataitems { get; set; } } 

when need filter elements specific type inherit dataitem, use oftype<t> method , example:

var ditemgroup= dc.dataitemgroups.firstordefault(); var extendeddataitems=ditemgroup.dataitems.oftype<extendeddataitem>();